Dictionary of Electrical 

WORDS f MMSANDPHRASES 



LIBRARY OF CONGRESS. 



Shelf Hfc£ 

W&r- 

UNITED STATES OF AMERICA. 



A. DICTIONARY 



OF 



ELECTRICAL WORDS 



TERMS AND PHRASES. 



^■BY 

EDWIN J. HOUSTON, A.M., 

PROFESSOR OF NATURAL PHILOSOPHY AND PHYSICAL GEOGRAPHY IN THE CENTRAL HIGH SCHOOL 

OF PHILADELPHIA ; PROFESSOR OF PHYSICS INT THE FRANKLIN INSTITUTE OF 

PENNSYLVANIA ; ELECTRICIAN OF THE INTERNATIONAL 

ELECTRICAL EXHIBITION, 

ETC., ETC. 



SECOND EDITION. RE WRITTEN AND GREA TL V ENLARGED. 



NEW YORK: 

the W. J. JOHNSTON COMPANY, limited, 
167-176 Times Building. 



1892; 



Copyright, 1889 and 1892, 
by the W. J. Johnston Company, limited. 



vC 



PREFACE TO THE FIRST EDITION. 

THE rapid growth of electrical science, and the almost daily addition to it of new 
words, terms and phrases, coined, as they too frequently are, in ignorance of 
those already existing, have led to the production of an electrical vocabulary that is 
already bewildering in its extent. This multiplicity of words is extremely discourag- 
ing to the student, and acts as a serious obstacle to a general dissemination of elec- 
trical knowledge, for the following reasons : 

1. Because, in general, these new terms are not to be found eve^ in the unabridged 
editions of dictionaries. 

2. The books or magazines, in which they were first proposed, are either inac- 
cessible to the ordinary reader, or, if accessible, are often written in phraseology un- 
intelligible except to the expert. 

3. The same terms are used by different writers in conflicting senses. 

4. The same terms are used with entirely different meanings. 

5. Nearly all the explanations in the technical dictionaries are extremely brief as 
regards the words, terms and phrases of the rapidly growing and comparatively new 
science of electricity. 

In this era of extended newspaper and periodical publication, new words are often 
coined, although others, already in existence, are far better suited to express the same 
ideas. The new terms are used for a while and then abandoned ; or, if retained, 
having been imperfectly defined, their exact meaning is capable of no little ambiguity; 
and, subsequently, they are often unfortunately adopted by different writers with such 
varying shades of meaning, that it is difficult to understand their true and exact 
significance. 

Then again, old terms buried away many decades ago and long since forgotten, are 
dug up and presented in such new garb that their creators would most certainly fail 
to recognize them. 

It has been with a hope of removing these difficulties to some extent that the author 
has ventured to present this Dictionary of Electrical Words, Terms and Phrases to his 
brother electricians and the public generally. 

He trusts that this dictionary will be of use to electricians, not only by showing the 
wonderful extent and richness of the vocabulary of the science, but also by giving the 
general consensus of opinion as to the significance of its different words, terms or 
phrases. It is, however, to the general public, to whom it is not only a matter of 
interest but also one of necessity to fully understand the esact meaning of electrical 
literature, that the author believes the book will be of the greatest value. 

In order to leave no doubt concerning the precise meaning of the words, terms and 
phrases thus defined, the following plan has been adopted of giving : 

(1.) A concise definition of the word, term or phrase. 

(2.) A brief statement of the principles of the science involved in the definition. 



IV 

(3.) Where possible and advisable, a cut of the apparatus described or employed 
in connection with the word, term or phrase denned. 

It will be noticed that the second item of the plan makes the Dictionary ap- 
proach to some extent the nature of an Encyclopedia. It differs, however, from 
an Encyclopedia in its scope, as well as in the fact that its definitions in all cases 
are concise. 

Considerable labor has been expended in the collection of the vocabulary, for 
which purpose electrical literature generally has been explored. In the alphabetical 
arrangement of the terms and phrases defined, much perplexity has arisen as to the 
proper catch-word under which to place them. It is believed that part of the 
difficulty in this respect has been avoided by the free use of cross references. 

In elucidating the exact meaning of terms by a brief statement of the principles 
of the science involved therein, the author has freely referred to standard textbooks on 
electricity, and to periodical literature generally. He is especially indebted to works 
or treatises by the following authors, viz. : S. P. Thompson, Larden, Cumming, 
Hering, Prescott, Ayrton, Ayrton and Perry, Pope, Lockwood, Sir William Thom- 
son, Fleming, Martin and Wetzler, Preece, Preece and Sivewright, Forbes, Max- 
well, De Watteville, J. T. Sprague, Culley, Mascart and Joubert, Schwendler, 
Fontaine, Noad, Smee, Depretz, De la Rive, Harris, Franklin, Cavallo, Grove, 
Hare, Daniell, Faraday and very many others. 

The author offers his Dictionary to his fellow electricians as a starting point only. 
He does not doubt that his book will be found to contain many inaccuracies, ambig- 
uous statements, and possibly doubtful definitions. Pioneer work of this character 
must, almost of necessity, be marked by incompleteness. He, therefore, invites 
the friendly criticisms of electricians generally, as to errors of omission and commis- 
sion, hoping in this way to be able finally to crystallize a complete vocabulary of 
electrical words, terms and phrases. 

The author desires in conclusion to acknowledge his indebtedness to his friends, 
Mr. Carl Hering, Mr. Joseph Wetzler and Mr. T. C. Martin, for critical exami- 
nation of the proof sheets ; to Dr. G. G. Faught for examination of the proofs of 
the parts relating to the medical applications of electricity, and to Mr. C. E. Stump 
for valuable aid in the illustration of the book ; also to Mr. George D. Fowle, 
Engineer of Signals of the Pennsylvania Railroad Company, for information concern- 
ing their System of Block Signaling, and to many others. 

EDWIN J. HOUSTON. 
Central High School, Philadelphia, Pa., 
September, 1889. 



PREFACE TO THE SECOND EDITION. 

THE first edition of the "Dictionary of Electrical Words, Terms and Phrases" met 
with so favorable a reception that the entire issue was soon exhausted. 
Although but a comparatively short time has elapsed since its publication, electrical 
progress has been so marked, and so many new words, terms and phrases have been 
introduced into the electrical nomenclature, that the preparation of a new edition has 
been determined on rather than a mere reprint from the old plates. 

The wonderful growth of electrical science may be judged from the fact that the 
present work contains more than double the matter and about twice the number of 
definitions that appeared in the earlier work. Although some of this increase has 
been due to words which should have been in the first edition, yet in greater part it 
has resulted from an actual multiplication of the words used in electrical literature. 

To a certain extent this increase has been warranted either by new applications of 
electricity or by the discovery of new principles of the science. In some cases, how- 
ever, new words, terms or phrases have been introduced notwithstanding the fact that 
other words, terms or phrases were already in general use to express the same ideas. 

The character of the work is necessarily encyclopedic. The definitions are given 
in the most concise language. In order, however, to render these definitions intel- 
ligible, considerable explanatory matter has been added. 

The Dictionary has been practically rewritten, and is now, in reality, a new book 
based on the general lines of the old book, but considerably changed as to order of 
arrangement and, to some extent, as to method of treatment. 

As expressed in its preface, the author appreciates the fact that the earlier book 
was tentative and incomplete. Though the wide scope of the second edition, the 
vast number of details included therein, and the continued growth of the electrical 
vocabulary must also necessarily make this edition incomplete, yet the author ventures 
to hope that it is less incomplete than the first edition. He again asks kindly criti- 
cisms to aid him in making any subsequent edition more nearly what a dictionary of 
so important a science should be. 

The order of arrangement in the first edition has been considerably changed. The 
initial letter under which the term or phrase is defined is in all cases that of the noun. 

For example, "Electric Light " is denned under the term " Light, Electric " ; 

" Diameter of Commutation " under " Commutation, Diameter of ," "Alter- 
nating Current Dynamo-Electric Machine" under "Machine, Dynamo-Electric, 
Alternating Current — ." As before, the book has numerous cross references. 

Although the arrangement of the words, terms and phrases under the initial letter 
of the first word, term or phrase, as, for example, " Electric Light " under the letter E, 
might possess some advantages, yet, in the opinion of the author, the educational value 



VI 

of the work would be thereby considerably decreased, since to a great extent such an 
arrangement would bring together incongruous portions of the science. 

Frequent cross references render it possible to use the Dictionary as a text-book in 
connection with lectures in colleges and universities. With such a book the student need 
make notes only of the words, terms or phrases used, and afterwards, by the use of the 
definitions and explanatory matter connected therewith, work up the general subject 
matter of the lecture. The author has successfully used this method in his teaching. 

In order to separate the definitions from the descriptive matter, two sizes of type 
have been used, the definitions being placed in the larger sized type. 

In the descriptive matter the author has not hesitated to quote freely from standard 
electrical works, electrical magazines, and periodical literature generally. Among the 
numerous works consulted, besides those to which reference has already been made 
in the preface to the first edition, he desires to acknowledge his indebtedness espe- 
cially to "The Alternating Current Transformer," by J. A. Fleming ; to various works 
of John W. Urquhart; to "Modern Views of Electricity," by Prof. O. J. Lodge; to 
"A Text-book of Human Physiology," by Landois & Sterling; and to "Practical 
Application of Electricity in Medicine and Surgery," by Liebig & Rohe. 

The cuts or diagrams used in the book have either been drawn especially for the 
work or have been taken from standard electrical publications. 

The chart of standard electrical symbols and diagrams has been taken from Prof. 
F. B. Crocker's paper on that subject. 

The definition of terms used in systems of electric railways have been taken 
mainly from a paper on ■" Standards in Electric Railway Practice," by O. T. Crosby. 

The author desires especially to express his obligations to Prof. F. B. Crocker of 
the Electrical Engineering Department, Columbia College, New York, and to Carl 
Hering, of Philadelphia, for critical examination of the entire manuscript and for many 
valuable suggestions ; also to The Electrical World and the Electrical Engineer of New 
York, and to Prof. Elihu Thomson, Edward Caldwell, T. C. Martin, Dr. Louis Bell, 
Joseph Wetzler, Nikola Tesla, Wm. H. Wahl, Prof. Wm. D. Marks, Prof. A. E. 
Dolbear, C. W. Pike, John Hoskin, and numerous others, for aid in connection with 
new words or phrases. So far as they relate to the medical applications of electricity, 
the proof sheets were revised by Dr. G. G. Faught, of Philadelphia. 

The author desires to thank critics of the first edition and the electrical fraternity in 
general for valuable suggestions. He presents this second edition of his Dictionary in the 
hope that it may to some extent properly represent the vocabulary, of electrical science. 

Central High School, EDWIN J. HOUSTON. 

Philadelphia, May, 1892. 



A. DICTIONARY 



OF 



ELECTRICAL 

WORDS, TERMS AND PHRASES 



A. or An. — An abbreviation sometimes used 
in medical electricity for anode. (See Anode.) 

A. C. C. — An abbreviation used in medical 
electricity for Anodic Closure Contraction. 
(See Contraction, Anodic Closure^ 

A. D. C. — An abbreviation used in medical 
electricity for Anodic Duration Contraction. 
(See Co?itraction, A?iodic Duration?) 

A. 0. C. — An abbreviation used in medical 
electricity for Anodic Opening Contraction. 
(See Contraction, Anodic Opening?) 

Abscissa of Rectilinear Co-ordinates. — A 
line or distance cut off along axis of abscissas. 

The abscissa of the point D, Fig. I, on the curve 
O D R, is the distance D I, or its equal A 2, 
measured or cut off on the line A C, the axis of 
abscissas; or, briefly, A 2, is the abscissa of the 
point D. 

Abscissas, Axis of — One of the 

axes of co-ordinates used for determining the 
position of points on a curved line. 

Thus the position of 
the point D, Fig. 1, on 
the curved line O D R, 
is determined by the per- 
pendicular distances, D 1 
and D 2, of such point 
from two straight lines, 
A B and A C, called the 
axes of co-ordinates. AC, A 2 C 

is CaUed the axis of ab- Fi ^ J ' Axes 0/ Co-ordinates, 
scissas, and AB, the axis of ordinates. The point 




A, where the lines are considered as starting or 
originating, is called the. point of origin, or, gen- 
erally, the origin. 

The use of co-ordinates was first introduced by 
the famous mathematician, Des Cartes. 

Absolute. — Complete in itself. 

The terms absolute and relative are used in 
electricity in the same sense as ordinarily. 

Thus, a galvanometer is said to be calibrated 
absolutely when the exact current strengths re- 
quired to produce given deflections are known ; 
or, in other words, when the absolute current 
strengths are known ; it is said to be calibrated 
relatively when only the relative current strengths 
required to produce given deflections are known. 

The word absolute, as applied to the units em- 
ployed in electrical measurements, was introduced 
by Gauss to indicate the fact that the values of 
such units are independent both of the size of the 
instrument employed and of the value of gravity at 
the particular place where the instrument is 
used. 

The word absolute is also used with reference 
to the fact that the values of the units could 
readily be redetermined from well known con- 
stants, in case of the loss of the standards. 

The absolute units of length, mass, and time 
are more properly called the C. G. S. units, or 
the centimetre-gramme-second units. (See Units, 
Absolute. ) 

An absolute system of units based on the milli- 
gramme, millimetre, and second, was proposed by 
Weber, and was called the millimetre milli- 
gramme-second units. It has been replaced by 



Aba.] 



4 



[Ace* 



the C. G. S. units. (See Units, Centimetre- 
Gramme- Second. Units, Fundamental.) 

Absolute Block System for Railroads. — 

(See Block System for Railroads, Absolute?) 

Absolute Calibration. — (See Calibration, 
Absolute?) 

Absolute Electrometer. — (See Electro7ne- 
ter, Absolute?) 

Absolute Galvanometer. — (See Galva- 
nometer, Absolute?) 

Absolute Unit of Current. — (See Current, 
Absolute Unit of?) 

Absolute Unit of Electromotive Force. — 
(See Force, Electromotive, Absolute Unit 
of) 

Absolute Unit of Inductance. — (See In- 
ductance, Absolute Unit of) 

Absolute Unit of Resistance. — (See Re- 
sistance, Absolute Unit of) 

Absolute Unit of Self-induction. — (See 
Induction, Self, Absolute Unit of) 

Absolute Units. — (See Units, Absolute?) 

Absolute Vacuum. — (See Vacuum, Ab- 
solute?) 

Absorption. — The taking, or, literally, 
drinking in, of one form of matter by another, 
such as a gas, vapor or liquid by a solid ; or 
of the energy of sound, light, heat, or elec- 
tricity by ordinary matter. 

Absorption, Acoustic The taking 

in of the energy of sound waves produced by 
one sounding or vibrating body by another 
vibrating body. 

Acoustic absorption may result in the dissipa- 
tion of the absorbed energy, as heat, or in sym- 
pathetic vibrations. (See Vibrations, Sympathetic.) 

Absorption, Electric The appar- 
ent soaking of an electric charge into the 
glass or other solid dielectric of a Leyden jar 
or condenser. (See Condenser?) 

The capacity of a condenser varies with the 
time the condenser remains charged and with the 
time taken in charging. Some of the charge 
acts as if it soaked into the solid dielectric, and 
this is the cause of the residual charge. (See 
Charge, Residual.) Therefore, when the con- 



denser is discharged, less electricity appears than 
was passed in ; hence the term electric absorption. 

Absorption, Luminous The ab- 
sorption of the energy of light in its passage 
through bodies. 

When sunlight falls on an opaque colored body, 
such for example as a red body, all the colors but 
the reds are absorbed. The reds are then thrown 
off and thus cause the color. In the same manner, 
when sunlight falls on a transparent colored body, 
such for example as red, all colors but the reds are 
absorbed, and the reds are transmitted. 

When sunlight falls on a phosphorescent body, 
a part of the light is absorbed as heat ; another 
part is absorbed by the molecules being set into 
motion sufficiently rapid to cause them to emit 
light or to become luminous. 

A mass of glowing gas or vapor absorbs waves 
of light of the same length as those it itself emits. 
This is the cause of the dark lines of the solar 
spectrum, called the FraunhofFer lines. 

The amount of light absorbed by the glass globe 
of an incandescent lamp, according to Urquhart, 
is as follows, viz.: 

Clear glass io per cent. 

Ground glass 35 " 

Opalescent glass 50 " 

Absorption, Selective The absorp- 
tion of a particular or selected character of 
waves of sound, light, heat, or electricity. 

Absorption, Thermal — The ab- 
sorption of heat energy in its passage through 
a body. 

The phenomena of thermal absorption are 
similar to those of luminous absorption. A sub- 
stance that is transparent to heat, or which allows 
heat waves to pass through without absorption, 
is called diathermanous, or diathermanic, or 
is said to be transparent to heat. 

Absorptive Power. — (See Power, Absorp- 
tive?) 

Acceleration. — The rate of change of 
velocity. 

Acceleration is thus distinguished from velocity: 
velocity expresses in time the rate-of-change of 
position, as a velocity of three metres per second ; 
acceleration expresses in time the rate-of-change 
of velocity, as an acceleration of one centimetre 
per second. 

Since all matter is inert, and cannot change its 



Ace] 



[Ace. 



condition of rest or motion without the applica- 
tion of some force, acceleration is necessarily due 
to some force outside the matter itself. A force 
may therefore be measured by the acceleration it 
imparts to a given mass of matter. 

Acceleration is positive when the velocity is in- 
creasing, and negative when it is decreasing. 

Acceleration, Dimensions of The 

value of the acceleration expressed in terms 
of the length or of distance by the time. (See 
Acceleration, Unit of) 

Acceleration, Unit of — That ac- 
celeration which will give to a body unit- 
velocity in unit-time ; as, for example, one 
centimetre-per-second in one second. 

Bodies falling freely in a vacuum, and ap- 
proximately so in air, acquire an acceleration 
which in Paris or London, at the end of a second, 
amounts to about 981 centimetres per second, or 
nearly 32.2 ft. per second. 

V 
A = — , or, in other words, 

The acceleration equals the velocity divided by 
the time. 

But, since velocity equals the Distance, or the 

L 



Length traversed in a Unit of Time, V = 



T* 



Therefore, A = 



The acceleration equals the length, or the dis- 
tance passed through, divided by the square of the 
time in seconds. 

These formulae represent the Dimensions of 
Acceleration. 

Accumulated Electricity. — (See Electri- 
city, Accumulated) 

Accumulating- Electricity. — (See Electri- 
city, Accumulating) 

Accumulation of Electricity. — (See Elec- 
tricity, Accumulation of) 

Accumulator. — A word sometimes applied 
to any apparatus in which the strength of a 
current is increased by the motion past it of a 
conductor, the currents produced in which 
tend to strengthen and increase the current 
which causes the induction. 



The word accumulator is sometimes applied to 
Sir Wm. Thomson's Electric Current Accumu- 
lator. 

Current accumulators operate on the reaction 
principle of dynamo-electric machines. In this 
sense, therefore, a dynamo -electric machine is an 
accumulator. (See Machine, Dynamo- Electric, 
Reaction Principle of.) 




I —- _ F 

Fig. 2. Barlows Wheel. 

The copper disc D, Fig. 2, has freedom of 
rotation, on a horizontal axis at O, in a magnetic 
field, the lines of force of which, represented by 
the dotted lines in the drawing, pass downward 
perpendicularly into the plane of the paper. 

If, now, a current from any source be passed 
in the direction A, O, B, C, A, through the circuit 
A, O, B, C, A, which is provided with spring 
contacts at O, and A, the disc will rotate in the 
direction of the curved arrow. This motion is 
due to the current acting on that part of the disc 
which lies between the two contacts — A and O. 
This apparatus is known as Barlow's Wheel. 

If, when no current is passing through the 
circuit, the disc be turned in the direction of the 
arrow, a current is set up in such a direction as 
would oppose the rotation of the disc. (See 
Law, Lenz's.) 

If, however, the disc be turned in the opposite 
direction to that of the arrow, induction currents 
will as before be produced in the circuit. As 
this rotation of the disc tends to move the circuit 
O A, towards the parallel but oppositely directed 
circuit B C, these two circuits being parallel and 
in opposite directions tend to repel one another, 
and there will thus be set up induced currents 
that tend to oppose the motion of rotation, and 
the current of the circuit will therefore increase 
in strength. (See Dynamics, Electro.) Should 
then a current be started in the circuit, and the 
original field be removed, the induction will be 
continued, and a current which, up to a certain 
extent, increases or accumulates, is maintained in 
the circuit during rotation of the disc. (Harden. ) 

Barlow's Wheel, when used in this manner, is 
known as Thomson's Electric Current Accumu- 
lator. 



Ace] 



6 



[Ace. 



Accumulator. — A word often applied to 
a Leyden jar or condenser, which permits the 
gradual collection from an electric source of 
a greater charge than it would otherwise be 
capable of containing. 

A condenser. (See Condenser^) 

The ability of a source to accumulate an in- 
creased charge when connected to a condenser is 
■due to the increased capacity which a plate or 
other conductor acquires when placed near 
another plate or conductor. (See Condenser. 
Jar, Leyden.) 

Accumulator, Capacity of The 

capacity of a condenser, expressed in micro- 
farads. (See Condenser, Capacity of.) 

Accumulator or Condenser ; Laws of Ac- 
cumulation of Electricity. — Sir W. Snow 
Harris, by the use of his Unit-Jar and Elec- 
tric Thermometer, deduced the following 
laws for the accumulation of electricity, which 
we quote from Noad's " Student's Text-Book 
of Electricity," revised by Preece : 

(i.) "Equal quantities of electricity are given 
off at each revolution ot the plate of an electrical 
machine to an uncharged surface, or to a surface 
charged to any degree of saturation. ' ' 

(2. ) "A coated surface receives equal quantities 
of electricity in equal times ; and the number of 
revolutions of the plate is a fair measure of the 
relative quantities of electricity, all other things 
remaining the same." 

(3 . ) " The free action of an electrical accumula- 
tion is estimated by the interval it can break 
through, and is directly proportional to the quan- 
tity of electricity." 

(4.) " The free action is inversely proportional 
to the surface." 

(5.) " When the electricity and the surface are 
increased in the same ratio, the discharging in- 
terval remains the same ; but if, as the electricity 
is increased, the surface is diminished, the dis- 
charging interval is directly as the square of the 
quantity of electricity." 

(6.) " The resistance of air to discharge is as 
the square of the density directly." 

According to some later investigations, the 
quantity a plane surface can receive under a given 
density depends on the linear boundary of the 
surface as well as on the area of the surface. 

" The amount of electrical charge depends on 



surface and linear extension conjointly. There 
exists in every plane surface what may be termed 
an electrical boundary, having an important rela- 
tion to the grouping or disposition oi the electric 
particles in regard to each other and to surrounding 
matter. This boundary in circles or globes is 
represented by their circumferences. In plane 
rectangular surfaces, it is by their linear extension 
or perimeter. If this boundary be constant, their 
electrical charge varies with the square root of 
the surface. If the surface be constant the charge 
varies with the square root of the boundary. If 
the surface and boundary both vary, the charge 
varies with the square root of the surface multi- 
plied into the square root of the boundary. " 

These laws apply especially to continuous sur- 
faces taken as a whole, and not to surfaces divided 
into separate parts. 

By electrical charge Harris meant the quantity 
sustained on a given surface under a given elec- 
trometer indication ; by electrical intensity, he 
meant the indication of the electrometer corre- 
sponding to a given quantity on a given surface. 

(See Condenser, Capacity of. Capacity, Elec- 
trostatic. Capacity, Specific Inductive. ) 

Accumulators of this character are now 
generally called Condensers. (For more modern 
principles concerning their construction and 
capacity see Condenser. Condenser, Capacity of.) 

Accumulator, Secondary or Storage 
Cell Two inert plates partially sur- 
rounded by a fluid incapable of acting chem- 
ically on either of them until after the passage 
of an electric current, when they become 
capable of furnishing an independent electric 
current. 

This use of the term accumulator is the one 
most commonly employed. A better term for 
such a cell is a secondary or storage cell. (See 
Cell, Secondary or Storage.) 

Commercially, an accumulator consists of a 
single jar and its electrolyte, in which a single 
set of positive and negative plates is properly 
placed. 

Accumulator, Water-Dropping 

An apparatus devised by Sir W. Thomson for 
increasing the difference of potential between 
two electric charges. 

The tube X Y, Fig. 3, connects with a reser- 
voir of water which is maintained at the zero 
potential of the earth. The water escapes from 



Ach, 



[Act. 




the openings at C and D, in small drops and falls 
on funnels provided, as shown, to receive the 
separate drops and again discharge them. 

The vessels A, A', and B, .. 

B', which are electrically X [f Y 

connected as shown, are 
maintained at a certain small A f, 
difference of potential, as 
indicated by the respective 
-f- and — signs. 

Under these circum- 
stances, therefore, C and D, 
will be charged inductively Fi S- 3- Water-Drop- 
With Charges Opposite to ^ Accumulator. 
those of A and B, or with — and -j- electricities 
respectively. As the drops of water fall on the 
funnels, the charges which the funnels thus con- 
stantly receive are given up to B' and A', before 
the water escapes. Since, therefore, B, B', and 
A, A', are receiving constant charges, the differ- 
ence of potential between them must continually 
increase. This apparatus operates on the same 
principle as the replenisher. The drops of water 
act as the carriers, and A, A', and B, B', as the 
hollow vessels. (See Replenisher.) 

Achromatic. — Free from false coloration. 

Images formed by ordinary lenses do not pos- 
sess the true colors of the object, unless the edges 
of the lenses are cut off by the use of a diaphragm ; 
i. e., an opaque plate with a central circular 
opening. The edges of the lenses disperse the 
light like an ordinary prism, and so produce rain- 
bow colored (prismatic) fringes in the image. 
The use of an achromatic lens is to obviate this 
false coloration. 

Achromatizahle. — Capable of being freed 
from false coloration. 

Achromatize. — To free from false color- 
ation. 

Achromatizing". — Freeing from false color- 
ation. 

Acid, Spent A battery acid, or other 

acid, that has become too weak for efficient 
action. 

In a voltaic cell the acid of the electrolyte 
becomes spent by combining with the metal of 
the positive plate. 

Acidometer. — A special form of hydrom- 
eter used in determining the specific gravity 
of the acid liquid in a secondary- or storage 



cell. (See Areometer or Hydrometer. Cell. 
Storage) 

The scale on the acidometer tube is made to in- 
dicate the density according to the distance the 
floating instrument sinks in the liquid. 

Aclinic Line. — (See Line, Aclinic.) 

Acoustic Absorption. — (See Absorption, 
Acoustic) 

Acoustic Engraving". — (See Engraving, 
Acoustic) 

Acoustic Telegraphy. — (See Telegraphy, 
Acoustic) 

Acoustic Tetanus. — (See Tetanus, Acous- 
tic) 

Acoutemeter, Electric An ap- 
paratus for electrically testing the delicacy of 
hearing. 

The Acoutemeter is one of the many applica- 
tions of Hughes' sonometer. It consists of three 
flat coils placed parallel to one another on a grad- 
uated rod, passing through their axes. The 
central coil, which is used as the primary of an 
induction coil, is fixed. The other two, which are 
employed as secondary coils, are movable. (See 
Sonometer, Hughes\ Coil, Induction. Micro- 
phone.) A microphone, electrical tuning fork, 
switches, plugs, and other accessories, are suitably 
placed and connected. The subject whose hear- 
ing is to be tested is placed with his back to the 
apparatus, and with two telephone receivers tightly 
fixed to his ears. As various sounds are produced , 
the outer or movable cods are moved gradually 
away from the central coil, until no sound is 
heard in the telephone receivers. This distance 
is in the inverse ratio of the delicacy of hearing of 
the individual. 

Actinic Photometer. — (See Photometer, 
Actinic) 

Actinic Ray. — (See Ray, Actinic) 

Actinism. — The chemical effects of light, 
as manifested by the decomposition of various 
substances. 

Under the influence of the sun's light, the car- 
bonic acid absorbed by the leaves of plants is de- 
composed in the living leaves into carbon, which is 
retained by the plant for the formation of its 
woody fibre or ligneous tissue, and oxygen, which 
is thrown off. 



Act.] 



[Act. 



The bleaching of curtains, carpets, and other 
fabrics exposed to sunlight is caused by the actinic 
power of the light. The photographic picture is 
impressed by the actinic power of light on a plate 
covered with some sensitive metallic salt. 

Actinograph. — An apparatus for measur- 
ing and recording the intensity of the chemi- 
cal effects of light. 

Actinography. — The method of measuring 
and recording the intensity of the chemical 
effects of light. 

Actinometer. — A word sometimes applied 
to a pyrheliometer. (See Pyrheliometer) 

Actinometer, Electric An appa- 
ratus for electrically measuring the intensity 
of the chemically active rays present in any 
luminous radiation. 

The rays from the luminous source are per- 
mitted to fall on a selenium resistance, and their 
intensity determined by the change observed in 
the resistance as indicated by the deflections of a 
galvanometer placed in circuit with the selenium 
resistance. Or, a thermo-electric pile is employed, 
and the amount of heat present determined by the 
indications of a galvanometer placed in its 
circuit. 

Action, Cataphoric The action 

of electric osmose or cataphoresis. (See 
Catapkoresis.) 

Action Currents. — (See Currents, Action) 

Action, Inductive, Lines of — 

Lines within the space, separating a charge 
and a neighboring body, along which elec- 
trostatic inductive action takes place. 

Lines of electrostatic force. 

Lines of inductive action pass through the 
dielectric, separating the two bodies, and termi- 
nate on the surfaces of the conductor. According 
to the now generally received notions, the elec- 
trostatic charge exists in the mass of the dielectric, 
and not in that of the conductor. The lines of 
inductive action terminate against the surfaces, 
one at the positive, and the other at the negative 
surface. A true E. M. F. exists in the space 
traversed by lines of inductive action. A con- 
ductor brought into this space becomes electri- 
fied, or is strained in such a manner that a 
momentary current is produced by the rearrange- 



ment of the electrification brought about by 
electrostatic induction. 

Action, Local, of Dynamo-Electric Ma- 
chine The loss of energy in a dy- 
namo-electric machine by the setting up of 
eddy currents in its pole pieces, cores, or 
other conducting masses. (See Currents, 
Eddy.) 

In a dynamo-electric machine local action is 
obviated by a. lamination of the pole pieces, arma- 
ture core, etc. (See Core, Lamination of.) 

Action, Local, of Yoltaic Cell 



An irregular dissolving or consumption of the 
zinc or positive element of a voltaic battery, by 
the fluid or electrolyte, when the circuit is 
open or broken, as well as when closed, or in 
regular action. 

Local action is due to small particles of such 
impurities as carbon, iron, arsenic, or other 
negative elements, in the positive plate. These 
impurities form with the positive element minute 
voltaic couples, and thus direct the corrosive 
action of the liquid to portions of the plate near 
them. Local action causes a waste of energy. 
It may be avoided by the amalgamation of the 
zinc. (See Zinc, Amalga)?iatio)i of.) 

Action, Mag-ne-Crystallic A term 

proposed by Faraday to express differences 
in the action of magnetism on crystalline 
bodies in different directions. 

A needle of tourmaline, if hung with its axis 
horizontal, is no longer paramagnetic, as usual, 
but diamagnetic. The same is true of a crystal 
of bismuth. Faraday concluded from these ex- 
periments that a force existed distinct from either 
the paramagnetic or the diamagnetic force. He 
called this the magne-crystallic force. 

Pliicker infers from these phenomena that a 
definite relation exists between the tiltimate form 
of the particles of matter and their magnetic be- 
havior. The subject may be regarded as yet 
somewhat obscure. (See Polarity, Diamagnetic.) 

Action of a Current on a Magnetic Pole. 

— (See Current, Action of, on a Magnetic- 
Pole) 
Action, Refreshing-, of Current 

The restoration, after fatigue, of muscular and 
nervous excitability obtained by the action of 



Act.] 



LAer. 



voltaic alternatives. (See Alternatives, Vol- 
taic?) 

Activity. — The work done per second by 
any agent. (This term is but seldom used.) 

Work-per-second, or, as generally termed 
in the United States, Power, or Rate of 
Doing Work. (See Power?) 

Activity, Unit of A rate of work- 
ing that will perform one unit of work per 
second. 

In C. G. S. units, the activity of one erg per 
second. 

The C. G. S. unit of activity is very small. 
One Watt, the practical unit of activity or power, 
is equal to ten million ergs per second. (See 
Watt.) 

The unit of activity generally used for mechan- 
ical power is the horse-power, or 746 watts. 
(See Horse -Power.) 

Actual Cautery. — (See Cautery, Actual?) 
Acute Angle. — (See Angle, Acute?) 
Adapter. — A screw nozzle fitted to an elec- 
tric lamp, provided with a screw thread to en- 
able it to be readily placed on a gas bracket 
or chandelier in place of an ordinary gas 
burner. 

Adherence. — The quality or property of 
adhering. (See Adhesion?) 

Adherence, Magnetic Adhesion be- 
tween surfaces due to magnetic attraction. 

Magnetic adhesion has been applied, among 
other things, to a brake action on car wheels, 
either by causing them to adhere directly to the 
track or to a brake-block. 

Adhesion. — The mutual attraction which 
exists between unlike molecules. (See At- 
traction, Molecular?) 

The phenomena of adhesion are due to the 
mutual attraction of dissimilar molecules. 

Adhesion, Electric Adhesion be- 
tween surfaces due to the attraction of unlike 
electrostatic charges. 

Molecular adhesion must be distinguished from 
the attraction which causes a piece of dry and 
warmed writing paper, that has been rubbed by a 
piece of india-rubber, to stick to a papered wall. 
In this latter case the attraction between the wall 



and the paper is due to the mutual attraction of 
two dissimilar electrostatic charges. Molecular 
adhesion must also be distinguished from the at- 
traction of opposite magnetic poles. 

Adhesion, Galvanoplastic The ad- 
hesion of a galvanoplastic deposit or coating 
to surfaces subjected to electroplating. (See 
Plating, Electro?) 

Adiatherniancy. — Opacity to heat. 

A substance is said to be diathermanous when 
it is transparent to heat. Clear, colorless crys- 
tals of rock salt are very transparent both to light 
and to heat. Rock salt, covered with a layer or 
deposit of lampblack or soot, is quite transparent 
to heat. An adiathermanous body is one which 
is opaque to heat. 

Heat transparency varies not only with differ- 
ent substances, but also with the nature of the 
source from which the heat is derived. Thus, a 
substance may be opaque to heat from a non- 
luminous source, such as a vessel filled with boil- 
ing water, while it is comparatively transparent 
to heat from a luminous source, such as an incan- 
descent solid or a voltaic arc. 

A similar difference exists as regards transpar- 
ency to light. A colorless glass will allow light 
of any color to pass through it. A blue glass will 
allow blue light to pass freely through it, but will 
completely prevent the passage of any red light; 
and so with other colors. 

Adiathernianic. — Possessing the quality of 
adiathermancy. (See Adiathermancy?) 

Adjustable Condenser. — (See Condenser, 
Adjustable.) 

Adjuster, Cord A device for ad- 
justing the length of a pendant cord. 

Adjustment. — Such a regulation of any 
apparatus as will enable it to properly perform 
its functions. 

JEpinus' Condenser. — (See Condenser, 
sEpinus'?) 

Aerial Cable. — (See Cable, Aerial?) 

Aerial Cable, Suspending 1 Wire of 

(See Wire, Suspending, of Aerial Cable?) 

Aerial Line. — (See Line, Aerial?) 

Aerolites.— A name sometimes given to 
meteorites. 

Meteorites are masses of solids which pass 



Aff.] 



10 



[Ago- 



through the upper portions only of the earth's 
atmosphere on their approach to the orbit of the 
earth, or which fall through the air on the earth's 
surface from the sky. They are luminous at 
night and are followed by a train of fire. The 
luminosity is due to heat produced by friction 
through the air. Meteors frequently burst from 
the sudden expansion of their outer portions. 

Some meteorites are composed of nearly pure 
iron alloyed with nickel. The majority of them, 
however, are merely stones or oxidized sub- 
stances. Their average velocity is about 26 miles 
a second. 

Affinity, Chemical Atomic attrac- 
tion. 

The force which causes atoms to unite and 
form chemical molecules. 

Atomic or chemical attraction generally results 
in a loss of the characteristic qualities or proper- 
ties which distinguish one kind of matter from 
another. In this respect chemical affinity differs 
from adhesion, or the force which holds unlike 
molecules together. (See Adhesion. Attraction, 
Molecular.) If, for example, sulphur is mixed 
with lampblack, no matter how intimate the 
mixture, the separate particles, when examined 
by a magnifying glass, exhibit their peculiar color, 
lustre, etc. If, however, the sulphur is chemi- 
cally united with the carbon, a colorless, transpar- 
ent, mobile liquid, called carbon bisulphide, re- 
sults, that possesses a disagreeable, penetrating 
odor. 

Chemical affinity, or atomic combination, is in 
fluenced by a variety of causes, viz.: 

(1.) Cohesion. Cohesion, by binding the mole- 
cules more firmly together, opposes their mutual 
atomic attraction. 

A solid rod of iron will not readily burn in the 
flame of an ordinary lamp; but, if the cohesion be 
overcome by reducing the iron rod to filings, it 
burns with brilliant scintillations when dropped 
into the same flame. In this case the increase of 
surface and the increased temperature of the 
smaller particles also contribute to the result. 

(2.) Solution. Solution, by giving the molecules 
greater freedom of motion, favors their chemical 
combination. 

(3.) Heat. Heat sometimes favors atomic com- 
bination possibly by decreasing the cohesion, and, 
possibly, by altering the electrical relations of the 
atoms. If too great, heat may produce decom- 
position. There is for most substances a critical 



temperature below which chemical combination 
will not take place. (See Thermolysis.) 

(4-) Light. Decomposition, or the lessening of 
chemical affinity, through the agency of light, is 
called Actinism. Light also causes the direct 
combination of substances. A mixture of equal 
volumes of hydrogen and chlorine unites explo- 
sively when exposed to the action of full sunlight. 
(See Actinism.) 

(5.) Electricity. An electric spark will cause 
an explosive combination of a mixture of oxygen 
and hydrogen. Electricity also produces chemi- 
cal decomposition. (See Electrolysis.) 

Helmholtz accounts for the electro-chemical 
attraction of oxygen for zinc by supposing that all 
substances possess a definite amount of attraction 
for electricity, and that the attraction of zinc in 
this respect exceeds that of copper and the other 
metals. He thus regards the zinc as attracting 
its electric charge rather than as attracting the 
oxygen. Since both zinc and copper are dyad 
metals, this view, as will be seen, is at variance 
with later views. 

Chemical affinity may be caused by the opposite 
attractions of electrical charges naturally possessed 
by the atoms of matter. This would appear to be 
rendered probable by the law of electro-chemical 
equivalence. (See Equivalence, Electro-Chemical, 
Law of. Electricity, Atom of.) 

After Currents.— (See Currents, After?) 

Aging* of Alcohol, Electric (See 

Alcohol, Electric Aging of.) 

Agonal.— Pertaining to the agone. (See 
Agone.) 

Agone. — A line connecting places on the 
earth's surface where the magnetic needle 
points to the true geographical north. 

The line of no declination or variation of 
a magnetic needle. (See Needle, Magnetic, 
Declination of) 

As all the places on the earth where the mag- 
netic needle points to the true north may be ar- 
ranged on a few lines, it will be understood that 
the pointing of the magnetic needle to the true 
geographical north is the exception and not the 
rule. In many places, however, the deviation 
from the true geograpical north is so small that 
the direction of the needle may be regarded as 
approximately due north. 

Agonic. — Pertaining to the agone. 



Air.] 



11 



[Ala. 



Air-Blast for Commutators. — An inven- 
tion of Prof. Elihu Thomson to prevent the 
injurious action of destructive flashing at the 
commutator of a dynamo-electric machine. 

A thin, forcible blast of air is delivered through 
suitable tubes at points on the three-part commu- 
tator cylinder of the Thomson-Houston dynamo, 
where the collecting brushes bear on its surface. 
The effect is to blow out the arc or prevent its for- 
mation and thus avoid its destructive action on 
the commutator segments. The use of the air- 
blast also permits the free application of oil, thus 
further avoiding wear. 

B 8 




Fig. 4. Air-Blast on Commuta 

The blast-nozzles are shown at B 3 , B 3 , Fig. 4, 
near the collecting brushes. 

The air-supply is obtained from a blower at- 
tached directly to the shaft of the machine. Its 
construction and operation will be readily under- 
stood from an inspection of Fig. 5, in which the 




Fig. 5. The Thomson Blower. 

top is removed for ready examination of the 
interior parts. 

Air Churning. — (See Churning, Air.) 
Air Condenser. — (See Condenser, Air.) 
Air Field.— (See Field, Air.) 
Air-Gap.— (See Gap, Air) 
Air-Line Wire. — (See Wire, Air-Line) 
Air Magnetic Circuit. — (See Circuit, Air 
Magnetic) 

Air-Pump.— (See Pump, Air) 
Air-Pump, Oeissler's Mercurial — 

(See Pump, Air, Geissler's Mercurial) 



Air-Pump, Mechanical (See Pu?np y 

Air, Mechanical) 

Air-Pump, Mercurial (See Pu?np, 

Air, Mercurial) 

Air-Pump, Sprengel's Mercurial 

(See Pump, Air, Sprengel's Mercurial) 

Air-Space Cut-Out. — (See Cut-Out, Air- 
Space) 

Alarm, Burglar A device, generally 

electric, for automatically announcing the 
opening of a door, window, closet, drawer, or 
safe, or the passage of a person through a 
hallway, or on a stairway. 

Electric burglar-alarm devices generally consist 
of mechanism for the operation of an automatic 
make and -break bell on the opening or closing of 
an electric circuit. The bell may either continue 
ringing only while the contact remains closed, or, 
may, by the throwing on of a local circuit or 
battery, continue ringing until stopped by some 
non-automatic device, such as a hand-switch. 

The alarm-bell is stationed either in the house 
when occupied, or on the outside when the house 
is temporarily vacated, or may connect directly 
with the nearest police station. 

Burglar-alarm apparatus is of a variety of 
forms. Generally, devices are provided by means 
of which, in case of house protection, an annunci- 
ator shows the exact part where an entrance has 
been attempted. (See Annunciator, Burglar - 
Alarm.) Switches are provided for disconnecting 
all or parts of the house from the alarm when so 
desired, as well as to per- 
mit windows to be partly 
raised for purposes of ven- 
tilation without sounding 
the alarm. A clock is fre- 
quently connected with the 
alarm for the purpose of 
automatically disconnect- 
ing any portion of the 
house at or for certain in- 
tervals of time. 

Fig. 6 shows a burglar- Fig. 6. Burglar-Alar?n- 
alarm with annunciator, Annunciator. 

switches, switch-key, cut-off, and clock. 

Alarm, Burglar, Central-Station 

A burglar-alarm, the contact points of which 
are placed in the places to be protected, and 




Ala.] 



12 



[Ala. 



■connected by suitable circuits with alarms 
placed in a centrally located station. 

In a system of central-station burglar-alarms, a 
number of houses, factories, banks, etc., are all 
connected telegraphically with the nearest police 
station, or other central station, constantly pro- 
vided with police officers. A series of contacts are 
placed on doors, windows, safes and money draw- 
ers, and connected with alarms and annunciators 
placed in the central station. An unauthorized 
entrance, therefore, is automatically telegraphed 
to the central station and its exact location indi- 
cated on the annunciator. Systems of central- 
station fire-alarms are constructed on a similar 
plan. 

Alarm, Electric An automatic de- 
vice by which attention is called to the occur- 
rence of certain events, such as the opening 
of a door or window; the stepping of a person 
on a mat or staircase; the rise or fall of tem- 
perature beyond a given predetermined point; 
or, a device intended to call a person to a tel- 
egraphic or telephonic instrument. 

Electric-alarms are operated by means of the 
ringing of an electro-magnetic or mechanical bell, 




Fig. 7. Electrically Started Mechanical Alarm. 

which is electrically called into action by either 
closing or opening an electric circuit, generally 
the former. 

Electric-alarms may be divided into two classes, 
viz.: 

(1.) Mechanically operated alarms, or those in 



which the alarm is given by clock-work, started 
by means of an electric current. 

(2.) Those in which the alarm is both set in ac- 
tion and operated by an electric current. 

In Fig. 7 is shown the general construction of 
an electrically started mechanical alarm. The 
attraction of the armature B, by the electro-mag- 
net A, moves the armature lever pivoted at C, 
and thus releases the catch e, and permits the 
spring or weight connected with the clock move- 
ment to set it in motion and strike the bell. 

Electrically actuated alarm-bells are generally 
of the automatic make-and-break form. The 
striking lever is operated by the attraction of the 
armature of an electro -magnet, and is provided 
with a contact-point, so placed that when the 
hammer is drawn away from the bell, by the ac- 
tion of a spring, on the electro-magnet losing its 
magnetism, a contact is made, but when the ham- 
mer is drawn towards the bell the contact is open- 
ed. When, therefore, the hammer strikes the 
bell, the circuit is opened, and the electro-magnet 
releases its armature, permitting a spring to again 
close the contact by moving the striking lever 
away from the bell. Once set into action, these 
movements are repeated while there is battery 
power sufficient to energize the magnet. 

In Fig. 8, in which is shown an electrically ac- 
tuated alarm-bell, the battery terminals are con- 

T 




Fig. 8. Automatic Make-and-Break. 

-.ected with the right and left hand binding-posts, 
P and M. The hammer, K, is connected with a 
striking lever, which forms part of the circuit, 
and which is attached to the armature oi the elec- 
tro-magnet e. A metallic spring, g, bears against 
the armature when the latter is away from the 
magnet, but does not touch the armature when 
it is moved towards the magnet. A small sprmg 
draws the lever away from the magnet when no 
current is passing. The movements of the urma- 



Ala. 



I'd 



[Ale. 



ture thus automatically open and close the circuit 
•of the electro-magnet. 

This form of make-and-break is called an auto- 
matic make-and-break. 

Alarm, Electrically Operated — 



—An 

alarm that is maintained in operation by the 
electric current. (See Alarm, Electric?) 

Alarm, Electro-Mechanical — A 

mechanically operated alarm that is started 
or set in operation by means of an electric 
current. (See Alarm, Electric?) 

Alarm, Fire, Automatic An in- 
strument for automatically telegraphing an 
alarm from any locality on its increase in tem- 
perature beyond a certain predetermined point. 

Fire-alarms are operated by thermostats, or by 
.-means of mercurial contacts; i. e., a contact 
closed by the expansion of a column of mercury. 
4 See Ther?nostat. Contact, Mercurial.) 

In systems of fire-alarm telegraphs, the alarm 
is automatically soui.ded in a central police sta- 
tion and in the district fire-engine house. (See 
Telegraphy, Fire-Alar?n. ) 

Alarm, Mercurial Temperature 

An instrument for automatically telegraphing 
an alarm by means of a mercurial contact on 
a predetermined change of temperature. 

The action of mercurial contacts is dependent 
on the fact that, as the mercury expands more 
than glass by the action of heat, the mercury level 
reaches a contact-point placed in a glass tube and 
thus completes the circuit through its own mass, 
which forms the other or movable contact. 
Sometimes both contacts are placed on opposite 
sides of a tube and are closed when the mercury 
reaches them. 

Mercurial temperature or thermostat alarms 
are employed in hot-houses, incubators, tanks 
-and buildings for the purpose of maintaining a 
uniform temperature. 

Alarm, Telegraphic An alarm-bell 

for calling the attention of an operator to 
■a telegraphic instrument when the latter is of 
the non-acoustic or needle type. 

In acoustic systems of telegraphy the sounds 
themselves are generally sufficient. 

Alarm, Telephonic An alarm-bell 

for calling a correspondent to the receiving 
telephone. 



These alarms generally consist of magneto- 
electric bells. (See Bell, Magneto- Electric .) 

Alarm, Temperature An electric 

alarm automatically operated on a change of 
temperature. (See Alarm, Fire, Automatic?) 

Alarm, Thermostat An electric 

alarm that is thrown into action by a thermo- 
stat. (See Thermostat?) 

Alarm, Water or Liquid Level 

A device for electrically sounding an alarm 
when a water surface varies materially from 
a given level. 

An electric bell is placed in a circuit that is au- 
tomatically closed or broken by the movement of 
contact-points operated by the change of liquid 
level. 

A form of electric alarm for a water-level is 
shown in Fig. 9. The float is provided with 
contacts for closing an electric circuit, when it 
ei;her rings a bell, or, by its action on some form 
of automatic cut-off, stops the water. 





Fig. q. Water-Level Alarm. Fig. 10. 

When arranged with a double float, as shown 
in Fig. 10, the alarm may be made to signal 
either a too high or a too low water level. 

Alarm, Yale-Lock-Switch Burglar 

— An apparatus whereby the opening of a 
door by an authorized party provided with the 
regular key will not sound an alarm, but any 
other opening will sound such alarm. 




Fig. 11. Yale -Lock-Switch. 
A Yale -lock burglar- alarm switch is shown in 
Fig. 11. 

Alcohol, Electric Aging of A pro- 
cess for the rapid aging of alcohol, by ex- 



Ale. I 

posing it to the action of electrically produced 
ozone. 

Instead of the ordinary process of aging alco- 
hol, by exposing it in partially closed vessels to 
the action of air, it is exposed to the action of 
ozone, electrically produced. 

The ozone employed is obtained in substan- 
tially the usual way by the passage of a rapid 
succession of electric sparks through air. 

Alcohol, Electric Rectification of 

A process whereby the bad taste and odor of 
alcohol, due to the presence o'f aldehydes, 
are removed by the electrical conversion of 
the aldehydes into true alcohols through the 
addition of hydrogen atoms. 

An electric current sent through the liquid 
between zinc electrodes liberates oxygen and hy- 
drogen from the decomposition of the water. 
The nascent or atomic hydrogen converts the 
aldehydes into alcohol and deprives the pro- 
ducts of their fusel oil, while the oxygen forms 
insoluble zinc oxide. 

Algebraic Co-efficient. — (See Co-efficient, 
Algebraic?) 

Algebraic Notation. — (See Notation, Al- 
gebraic?) 

All-Night Arc Lamp. — (See Lamp, Ail- 
Night Arc.) 

All-Night Electric Lamp. — (See Lajnp, 
Ail-Night Arc) 

Allotropic— Pertaining to allotropy. (See 
Allotropy) 

Allotropic State.— (See State, Allotropic). 

Allotropy. — A variation of the physical 
properties of an elementary substance with- 
out change of composition of its molecules. — 
(See State, Allotropic) 

Alloy. — A combination, or mixture, of two 
or more metallic substances. 

Alloys in most cases appear to be true chemi- 
cal compounds. In a few instances, however, 
they may form simple mixtures. 

The composition of a few important alloys is 
here given: 

Solder, plumber's; Tin 66 parts, Lead 34 parts. 

Pewter, hard ; Tin 92 parts, Lead 8 parts. 

Britannia metal; Tin 100 parts, Antimony 8 
parts, Copper 4 parts, Bismuth, I part. 



14 [AIL 

Type metal; Lead 80, Antimony 20 parts. 
Brass, white; Copper 65, Zinc 35 parts. 
Brass, red; Copper 90, Zinc 10 parts. 
Speculum metal; Copper 67, Tin 33 parts. 
Bell metal; Copper 78, Tin 22 parts. 
Aluminium bronze; Copper 90, Aluminium 10 
parts. 

Alloy. — To form a combination or mixture 
of two or more metallic substances. 

Alloy, German Silver — An alloy 

employed for the wires of resistance coils, 
consisting of 50 parts of copper, 25 of zinc, 
and 25 of nickel. 

German silver wire is suitable for resistance 
coils, because its resistance varies but slightly with 
changes of temperature. It is cheaper th <m plati- 
num-silver alloy, and is therefore employed ex- 
tensively. Platinum silver alloy, however, ha&- 
more resistance for a given size of wire, and its re- 
sistance varies somewhat less than German silver 
with changes of temperature, and is therefore ust d> 
where greater accuracy is desired. 

Alloy, Palladium An alloy of pal- 
ladium with other metals. 

Palladium forms a number of useful alloys with 
various metals. Some of the palladium alloys are 
as elastic as steel, are unaffected by moisture or 
ordinary corrosive agencies, and are entirely de- 
void of paramagnetic properties; that is to say, 
they cannot be magnetized after the manner of 
iron. 

These properties have been utilized by their 
discoverer, Paillard, in their employment for the 
hair-springs, escapements and balance wheels of 
watches, in order to permit the watches to be car- 
ried into strong magnetic fields without any ap- 
preciable effects on the rate of the watch. A 
number of careful tests made by the author, by 
long continued exposure of watches, thus pro- 
tected by the Paillard alloys, in extraordinary 
fields, show that the protection thus given the 
watches enables them to be carried into the strong- 
est possible magnetic fields without appreciably^ 
affecting their rate. 

The Paillard palladium alloys have the follow- 
ing composition, viz. : 

Alloy No. 1. 

Palladium 60 to 75 parts. 

Copper 15 to 25 " 

Iron 1 to 5 " 



All.] 

Alloy No. 2. 

Palladium 5° to 75 P arts - 

Copper 20to30 " 

Iron 5 to2 ° " 

Alloy No. j. 

Palladium 651075 " 

Copper 15 to 25 " 

Nickel' 1 to 5 " 

Gold 1 to 2\ " 

Platinum \ to 2 " 

Silver 3 to 10 " 

Steel 1 to 5 " 

. Alloy No. 4. 

Palladium 451050 " 

Silver 20 to 25 " 

Copper 15 to 25 " 

Gold... 2 to 5 " 

Platinum 2 to 5 " 

Nickel 2 to 5 " 

Steel 2 to 5 " 

The great value of the palladium alloys, when 
employed for the hair-springs of watches, arises 
not only from their non-magnetizable properties, 
and their inoxidizability, but particularly from the 
fact that their elasticity is approximately the same 
for comparatively wide ranges of temperature. 

Alloy, Platinnin-Silver An alloy 

consisting of one part of platinum, and two 
parts of silver. 

Platinum silver all >y is now extensively em- 
ployed for resistance coils from the fact that 
changes in temperature of the alloy produce but 
comparatively small changes in its electrical re- 
sistance. (See Alloy, German Silver.) 

Alphabet, Telegraphic — An arbi- 
trary code consisting of dots and dashes, 
sounds,deflections of a magnetic needle, flashes 
of light, or movements of levers, following one 
another in a given predetermined order, to 
represent the letters of the alphabet and the 
numerals. 

Alphabet, Telegraphic : International 

Code The code of signals for letters, 

etc., employed in England and on the Euro- 
pean continent generally. 

Similar symbols are employed for the numerals 
and the punctuation marks. 

It will be observed that it is mainly in the 



15 [Alp. 

characters of the American Morse, in which spaces 
are used, that the Continental characters differ 
from the American. This is due to the use of the 
needle instrument with which a space cannot well 
be represented. A movement or deflection of the. 





Single 




Single 


Printing 


Needle 


Printing 


.Needle 


a — 

b 

c . 

d 


s/ 


n 

p 

q 


/// 


e . 

f " 

g 




r . . 

s ... 
t _ 


x/v 

/ 


h 


. VvW 


u 


vs/ 


.0 


./// 


v . 

w . 




k 

1 

m 




x .. 

z 





Itite> national Telegraphic Code. 

needle to the left signifies a dot; a movement tc* 
the right, a dash. 

Alphabet, Telegraphic : Morse's 



Various groupings of dots and dashes, or 
deflections of a magnetic needle to the right 
and left, which represent the letters of the 
alphabet or other signs. 

In the Morse alphabet dots and dashes are em- 
ployed in recording systems, and sounds of 
varying intervals, corresponding to the dots and 
dashes, in the sounder system. 

A dash is equal in length of time to three dots.. 
The space between the separate characters of a 
single letter is equal to one dot, except in the 
American Morse, in which the following letters 
contain longer spaces: C, O, R, Y, and Z. The 
lengthened spaces are equal to two dots. L is 
one and a half times the length of T. 

The sound produced by the down stroke of the 
sounding lever in the Morse sounder is readily- 
distinguishable from the up stroke. When these 
differences are taken in connection with the inter- 
vals between successive sounds there is no diffi- 
culty in reading by sound. 

(For methods of receiving the alphabet, see 
Sounder, Morse Telegraphic. Recorder, Morse.. 
Recorder, Bain's Chemical. Recorder, Siphon.. 
Relay. Magnet, Receiving. ) In the needle tele- 
graph, the code is similar to that used in the Morse 
Alphabet. (See 1 ' elegraphy, Single -Needle.) 



Alt.] 16 

American Morse Code. 
Alphabet. 

a n 

b o - - 

c -- - P 

d— - q---- 

e - r - -- 

i s --- 

g t- 

h u 

it. v 

J w 

k x 

1 y 

m z 

& - --- 

Numerals. 

i 6 

2 7 

3 8 

4 9 

5 o 

Punctuation Marks. 

Period Interrogation 

Comma Exclamation 

Printing Single Needle 

1 X //// 

2 s, /// 

3 \ x N // 

4 \ \ \ \ / 

5 \\\\\ 

6 / x \ \ \ 

7 //vw 

.8 ///\\ 

9 ////\ 

10 ///// 

Period www 

Comma \ / s / \ / 

interrogation __ \\ / / \\ 

Exclamation //\\// 

Colon // /\\\ 

Semicolon / \ /\ /\ 

Alteration Theory of Muscle or Nerve 

Current. — (See Theory, Alteration, of 
Muscle or Nerve Current?) 

Alternating" Arc. — (See Arc, Alternat- 
ing.) 

Alternating Current Circuit. — (See Cir- 
cuit, Alternating Current?) 



[Alt. 

Alternating" Current Condenser. — (See 
Condenser, Alternating Current?) 

Alternating- Current Dynamo-Electric 
Machine. — (See Machine, Dynamo-Electric , 
Alternating Current?} 

Alternating Current Electric Motor. — 

(See Motor, Electric, Alternating Current?) 

Alternating Currents. — (See Currents, 
Alternating?) 

Alternating Currents, Distribution of 
Electricity by (See Electricity, Dis- 
tribution of, by Alternating Currents?) 

Alternating Discharge. — (See Discharge, 
Alternating?) 

Alternating Dynamo-Electric Machine. — 
(See Machine, Dynamo-Electric , Alternat- 
ing Current?) 

Alternating Electrostatic Field. — (See 
Field, Alternating Electrostatic?) 

Alternating Electrostatic Potential. — 
(See Potential, Alternating Electrostatic?) 

Alternating Field. — (See Field, Alternat- 
ing?) 

Alternating Influence Machine, Wims- 

hurst's (See Machine, Wimshursfs 

Alternating Influence?) 

Alternating Magnetic Field. — (See Field, 
Alternating Magnetic?) 

Alternating Magnetic Potential. — (See 
Potential, AlterJiating Magnetic) 

Alternating Potential. — (See Potential, 
Alternating?) 

Alternating Primary Currents. — (See 
Currents, Alternating Primary?) 

Alternating Secondary Currents.— (See 
Currents, Alternating Secondary?) 

Alternation.— A change in direction or 
phase. 

Alternations. — Changes in the direction of 
a current in a circuit. 

A current that changes its direction 300 times 
per second is said to possess 300 alternations per 
second. 

Alternations, Complete A change 

in the direction of a current in a circuit from its 



Alt.] 



17 



[Amm. 



former direction and back again to that 
direction. A complete to-and-fro change. 

Complete alternations are sometimes indicated 
by the symbol ~. 

Alternations, Frequency of — A 

phrase employed to denote the number of al- 
ternations per second. 

Alternative Path. — (See Path, Alterna- 
tive^) 

Alternatives, Voltaic A term used 

in medical electricity to indicate sudden re- 
versals in the polarity of the electrodes of a 
voltaic battery. 

An alternating current from a voltaic bat- 
tery, obtained by the use of a suitable com- 
mutator. 

Sudden reversals of polarity produce more 
energetic effects of muscular contraction than do 
simple closures or completions of the circuit. 

The muscular contraction produced by a voltaic 
current is much stronger when the direction of the 
current is rapidly reversed by means of a com- 
mutator than when the current is more slowly 
broken and the poles then reversed. 

The effect of voltaic alternatives is to produce 
quick contractions that are in strong contrast to 
the prolonged contractions that result from the 
faradic current. In the faradic machine, the 
reversals are so rapid that the muscle fails to 
return to rest before it is again contracted. 

Voltaic alternatives are sometimes indicated by 
the contraction V. A. 

Alternator. — A name commonly given to 
an alternate current dynamo. (See Machine, 
Dynamo- Electric , Alternating Current) 

Alternator, Compensated Excitation of 

An excitation of an alternating current 

dynamo-electric machine, in which the field is 
but partially excited by separate excitement, 
the remainder of its exciting current being 
derived from the commuted currents of a 
small transformer placed in the main circuit 
of the machine. 

The object of compensated excitation of an 
alternator is to render the machine self-governing. 

Amalgam. — A combination or mixture 
of a metal. with mercury. 

A-nalgain, Electric A substance 



with which the rubbers of the ordinary fric- 
tional electric machines are covered. 

Electric amalgams are of various compositions. 
The following formula produces an excellent 
amalgam : 

Melt together five parts of zinc and three of 
tin, and gradually pour the molten metal into 
nine parts of mercury. Shake the mixture until 
cold, and reduce to a powder in a warm mortar. 
Apply to the cushion by means of a thin layer of 
stiff grease. 

Mosaic gold, or bisulphide of tin, and powdered 
graphite, both act as good electric amalgams. 

An electric amalgam not only acts as a con- 
ductor to carry off the negative electricity, but, 
being highly negative to the glass, produces a far 
higher electrification than would mere leather or 
chamois. 

Amalgamate. — To form into an amalgam. 

Amalgamating'. — Forming into an amal- 
gam. 

Amalgamation. — the act of forming into 
an amalgam, or effecting the combination of 
a metal with mercury. 

Amalgamation of Zinc Plates of Voltaic 
Cell. — (See Plates, Zinc, of Voltaic Cell, 
Amalgamation of) 

Amber. — A resinous substance, generally 
of a transparent, yellow color. 

Amber is interesting electrically as being be- 
lieved to be the substance in which the proper- 
ties of electric attractions and repulsions, imparted 
by friction or rubbing, were first noticed. It was 
called by the Greeks rj\EKtf)ov, from which the 
word electricity is derived. This property was 
mentioned by the Greek, Thales of Miletus, 600 
B. c, as well as by Theophrastus. 

American System of Telegraphy.— (See 

Telegraphy, American System of) 

American Twist-Joint. — (See Joi?it, 
American Twist) 

American Wire Gauge. — (See Gauge, 
Wire, American) 

Ammeter. — A form of galvanometer in 
which the value of the current is measured 
directly in amperes. (See Galvanometer.) 

An ampere-meter or ammeter is a commercial 
form of galvanometer in which the deflections of 



Amm.J 



18 



[Amp. 



a magnetic needle are calibrated or valued in am- 
peres. As a rule the coils of wire in an ammeter 
are of lower resistance than in a voltmeter. The 
magnetic needle is deflected from its zero position 
by the field produced by the current whose strength 
in amperes is to be measured. This needle is held 
in the zero position by the action of a magnetic 
field, either of a permanent or an electro-magnet, 
by the action of a spring, or by a weight under the 
influence of gravity. There thus exist a variety 
of ammeters, viz.: permanent-magnet ammeters, 
electro-magnetic ammeters, spring ammeters and 
gravity ammeters. 

In the form originally devised by Ayrton and 
Perry, the needle came to rest almost imme- 
diately, or was dead-beat in action. (See Damp- 
ing.) It moved through the field of a permanent 
magnet. The instrument was furnished with a 
number of coils of insulated wire, which could 
be connected either in series or in multiple -arc by 
means of a commutator, thus permitting the scale 
reading to be verified or calibrated by the use of a 
single voltaic cell. (See Circuits, Varieties of. 
Commutator. Calibration, Absolute. Calib> a- 
lion, Relative.) In this case the coils were 
turned to series, and a plug pulled out, thus intro- 
ducing a resistance of one ohm. 




Fig. i2. Ayrton and Perry Ammeter. 

Fig. 12 represents an ampere-meter devised by 
Ayrton and Perry. A device called a cotnmutator 
for connecting the coils either in series or parallel 
is shown at C. Binding posts are provided at 
P, PS, and S. The dynamo terminals are con- 
nected at the posts P, PS, and the current will 
pass only when the coils are in multiple, thus 
avoiding accidental burning of the coils. In this 
case the entire current to be measured passes 
through the coils so coupled. The posts S and 
PS, are for connecting the single battery cell cur- 
rent. 

A great variety of ampere-meters, or ammeters, 
have been devised. They are nearly all, how- 



ever, constructed on essentially the same general 
principles. 

Commercial ammeters are made in a ^reat va- 
riety of forms. When the currents to be meas- 
ured are large, as is generally the case in electric 
light or power stations, they consist of a coil of 
insulated wire, often of a single turn, or even of 
but a part of a turn, having a balanced coie of 
iron or steel capable of moving freely within it. 

Ammeter, Electro-Magnetic A 

form of ammeter in which a magnetic needle is 
moved against the field of an electro-magnet 
by the field of the current it is measuring. 
(See Aimneter?) 

— A form of am- 



Ammeter, Gravity — 

meter in which a magnetic needle is moved 
against the force of gravity by the field of the 
current it is measuring. (See Ammeter?) 

Ammeter, Magnetic- Vane An 

ammeter in which the strength of a magnetic 
field produced by the current that is to be 
measured is determined by the repulsion ex- 
erted between a fixed and a movable iron 
vane, placed in said field and magnetized 
thereby. (See Voltmeter, Magnetic- Vane.) 

Ammeter, Permanent-Magnet A 

form of ammeter in which a magnetic needle 
is moved against the field of a permanent mag- 
net by the field of the current it is measuring. 
(See Ammeter?) 

Ammeter, Reducteur for (See Re- 
duct eur, or Shunt for Ammeter?) 

Ammeter, Spring A form of am- 
meter in which a magnetic needle is moved 
against the action of a spring by the field of 
the current it is measuring. (See Ammeter?) 

Amorphous. — Having no definite crys- 
talline form. 

Mineral substances have certain crystalline 
forms, that are as characteristic of them as are the 
forms of animals or plants. Under certain cir- 
cumstances, however, they occur without definite 
crystalline form, and are then said to be amor- 
phous solids. 

Amperage. — The number of amperes pass- 
ing in a given circuit. 

The current strength in any circuit as indi- 
cated by an ampere-meter placed in the circuit. 



Amp.] 



19 



[Am 



Ampere. — The practical unit of electric 
current. 

Such a rate-of-flow of electricity as trans- 
mits one coulomb per second. 

Such a current (or rate-of-flow or trans- 
mission of electricity) as would pass with an 
electromotive force of one volt through a cir- 
cuit whose resistance is equal to one ohm. 

A current of such a strength as would 
deposit .005084 grain of copper per second. 

A current of one ampere is a current of such 
definite strength that it would flow through a cir- 
cuit of a certain resistance and with a certain 
electromotive force. (See Force, Electromotive. 
Volt. Resistance. Ohm.) 

Since the ohm is the practical unit of resistance, 
and the volt the practical unit of electromotive 
force, the ampere, or the practical unit of current, 
is the current that would flow through unit resist- 
ance, under unit pressure or electromotive force. 

To make this clearer, take the analogy of water 
flowing through a pipe under the pressure of a 
•column of water. That which causes the flow is 
the pressure or head ; that which resists the flow 
is the friction of the water against the pipe, which 
will vary with a number of circumstances. The 
rate -of -flow may be represented by so many cubic 
inches of water per second. 

As the pressure or head increases, the flow in- 
creases proportionally; as the resistance increases, 
the flow diminishes. 

Electrically, electromotive force corresponds to 

the pressure or head of the water, and resistance 

# to the friction of the water and the pipe. The 

ampere, which is the unit rate-of-flow ptr second, 

may therefore be represented as follows, 

E 



C 



R 



as was announced by Ohm in bis 



law. (See Law of Ohm.) 

This expression signifies that C, the current in 
amperes, is equal to E, the electromotive force in 
volts, divided by R, the resistance in ohms. 

We measure the rate-of-flow of liquids as so 
many cubic inches or cubic feet per second — that is, 
in units of quantity. We measure the rate-of-flow 
of electricity as so much electricity per second. 
The electrical unit of quantity is called the Coul- 
omb. (See Coulomb.) The coulomb is such a 
quantity as would pass in one second through a 
circuit in which the rate-of-flow is one ampere. 

An ampere is therefore equal to one coulomb per 
StC nd. 



The electro-magnetic unit of current is such a 
current that, passed through a conducting wire 
bent into a circle of the radius of one centimetre, 
would tend to move perpendicu'ar to its plane a 
unit magnetic pole htld at its centre, and 
sufficiently long to practically remove the other 
pole from its influence, with unit force, i. e., the 
force of one dyne. (See Dyne.) The ampere, or 
practical electro-magnetic unit, is one -tenth of 
such a current ; or, in other words, the absolute 
unit of current is ten amperes. 

An ampere may also be defined by the chemical 
decomposition the current can effect as measured 
by the quantity of hydrogen liberated, or metal 
deposited. 

Defined in this way, an ampere is such a cur- 
rent as will deposit .00111815 gramme, or 
.017253 grain, of silver per second on one of the 
plates of a silver voltameter, from a solution of 
silver nitrate containing from 15 to 30 per cent, of 
the salt (See Voltameter), or which will decompose 
.00009326 gramme, or .001439 grain of dilute 
sulphuric acid per second, or pure sulphuric acid 
at 59 degrees F. diluted with about 15 per cent, of 
water, that is, dilute sulphuric acid of Sp. Gr. of 
about I.I. The present scientific and commercial 
practice is to take the ampere to be such a current 
as will deposit 4 024 grammes of silver in one hour. 

Ampere Arc.— (See Arc, Ampere) 

Ampere-Feet. — (See Feet, Ampere.) 

Ampere-Hour. — (See Hour, Ampere) 

Ampere-Meter. — An ammeter. (See Am- 
meter) 

Ampere-Meter, Balance or Neutral Wire 

An ampere-meter placed in the cir- 
cuit of the neutral wire, in the three-wire sys- 
tem of electric distribution, for the purpose of 
showing the excess of current passing over 
one side of the system as compared with the 
other side, when the central wire is no longer 
neutral. 

Ampere-Minute. — (See Minute, Ampere^ 
Ampere Ring-. — (See Ring, Ampere) 
Ampere-Second. — (See Second, Ampere.) 
Ampere Tap. — (See Tap, Ainpkre) 
Ampere-Turn. — (See Tur?i, Ampere) 

Ampere-Turn, Primary (See Turn, 

Ampere, Primary) 



Amp.] 



20 



[Ane» 



Ampere-Turn, Secondary — (See 

Turn, Ampere, Secondary?) 

Ampere- Volt. — A watt, or the y^ of a 
horse-power. 

This term is generally written vdit-anipere. 
(See Volt- Ampere.) 

Ampere-Winding 1 . — (See Winding, Am- 
pere?) 

Ampere's Rule for Effect of Current on 
Needle. — (See Rule, Ampere's, for Effect of 
Current on Needle.) 

Ampere's Theory of Magnetism. — (See 
Magnetism, Ampere s Theory of.) 

Amperian Currents. — (See Currents, Am- 
perian) 

Amplitude of Vibration or Wave. — (See 
Vibration or Wave, Amplitude of) 

Ammunition-Hoist, Electric — An 

electrically operated hoist for raising ammu- 
nition to the deck of a ship. 

In the electric ammunition-hoist the electric 
motor which moves the hoist is made to follow the 
motions of the operator's hand, both as regards 
direction and speed. The motion of a crank, or 
wheel, causes a switch to start an electric motor in 
a certain direction, which tends to close the switch, 
thus necessitating a race between the operator 
and the motor. Should the operator begin to 
close the switch more slowly, the m tor will over- 
take him, will partially close the switch, and thus 
lower the speed of the motor. 

Analogous Pole. — (See Pole, Analogous) 

Analysis. — The determination of the com- 
position of a compound substance by separ- 
ating it into the simple or elementary sub- 
stances of which it is composed. 

Analysis, Electric The determin- 
ation of the composition of a substance by 
electrical means. 

Various processes have been proposed for elec- 
tric analysis; they consist essentially in decompos- 
ing the substance by means of electric currents, 
and are either qualitative or quantitative. (See 
Electrolysis.) 

Analysis, Electrolytic A term 

sometimes used instead of electric analysis. 
(See Analysis, Electric) 

Analysis, Qualitative A chemical 



analysis which merely ascertains the kinds of 
elementary substances present. 

Analysis, Quantitative A chemicaL 

analysis which ascertains the relative propor- 
tions in which the different components enter 
into a compound. 

Analyzable. — Separable into component 
parts. 

Analyze. — To separate into component 
parts. 

Analyze, Electrically To separate 

electrically into component parts. 

Analyzer, Electric A gridiron of 

metallic wires which is transparent to electro- 
magnetic waves, when its length is perpendic- 
ular to them, but opaque to them — i. e. y . 
possessing the ability to reflect them — when, 
rotated 90 degrees from its former position. 

The electric analyzer, it will be observed, is 
analogous to an analyzer for polarized light. A 
reflecting surface, for example, being able to re- 
flect polarized light in a given position, and unable- 
to reflect it when rotated 90 degrees from suck 
position, is capable of acting as an analyzer for 
p larized light. 

Analyzer, Gray's, Harmonic Telegraphic 

An electro-magnet, the armature of 

which consists of a steel ribbon stretched in 
a metallic frame and capable through regula- 
tion, as to tension, by means of a screw, o£ 
being tuned to a. certain note. 

The steel ribbon is thrown into vibration when- 
ever pulsations from the transmit 1 ing instruments 
are sent over the line corresponding to the rate cf 
motion of the ribbon, but is not set into vibration 
by any others. If, therefore, a number of different 
analyzer-, tuned to different notes, are placed on 
the same line, each will be operated only by the 
pulsations sent into the line corresponding to its. 
rate of motion, and thus multiple transmission in 
the same direction is possible. In order to 
strengthen the tones of the analyzers, each is pro- 
vided with a resonant air column. (See Reson- 
ator. Telegraphy, Multiplex.) 

Analyzing. — Separating into component: 
parts. 

Anelectric. — A word formerly applied ta 
bodies (conductors) which it was believed 
could not be electrified by friction. 



Aiie.] 



21 



LAnu 



This term is now obsolete. Conductors are 
easily electrifkd, when insulated. 

Anelectrotonic State. — (See State, Anelec- 
trotonic) 

Anelectrotonic Zone. — (See Zone, Anelec- 
trotonic?) 

Anelectrotonus. — In electro-therapeutics, 
the decreased functional activity which occurs 
in a nerve in the neighborhood of the anode, 
or positive electrode, when applied therapeu- 
tically. (See Electrotonus) 

Anemometer, Electric An appa- 
ratus to electrically record or indicate the direc- 
tion and intensity of the wind. 

In the electric recording anemometer, the force 
or velocity of the wind, or both, are recorded on 
a moving sheet of paper, on which the time is 
marked, so that the ( xact time of any given 
change is known. 

Anemoscope. — An instrument which indi- 
cates, but does not measure the intensity or 
record the direction of the wind. 

The word is often, though improperly, used in- 
terchangeably for anemometer. 

Angle. — The deviation in direction between 
two lines or planes that meet. 

Angles are measured by arcs of circles. The 
angle at B A C, Fig. 13, is the deviation of the 
straight line A B, from A 
C. In reading the let- 
tering of an angle the 
letter placed in the mid- 
dle indicates the angle 
referred to. Thus B A 
C, means the angle be- 
tween A Band AC; B A 
D, 




A C 

Fig. 13. Angles. 
the angle between B A and A D. Angles are 
valued in degrees, there being 360 degrees in an 
entire circumference or circle. Degrees are in- 
dicated thus: 90 , or ninety degrees. 

Angle, Acute An angle whose value 

is less than a right angle or 90 degrees. 

B A E, or E A D, in Fig. 13, is an acute angle. 

Angle, Complement of What an 

angle needs to make its value 90 degrees, or a 
right angle. 

Thus in Fig. 13, B A E, is the complement of 
the angle E A D, since B AE-fEAD = 90 
degrees. 



Angle, Obtuse An angle whose 

value is greater than a right angle or 90 
degrees. 

E A C, Fig. 13, is an obtuse angle. 

Angle of Declination or Variation.— (See 
Declination, Angle of. Variation, Angle of.) 

Angle of Difference of Phase Between 
Alternating' Currents of Same Period. — 
(See Phase, Angle of Difference of, Between 
Alternating Currents of Same Period?) 

Angle of Dip. — (See Dip. Dip or Incli- 
nation, Angle of) 

Angle of Inclination. — (See Dip or Incli- 
nation, Angle of) 

Angle of Lag- of Dynamo-Electric Ma- 
chine. — (See Lag, Angle of, of Dynamo- 
Electric Machine) 

Angle of Lead. — (See Lead, Angle of) 

Angle of Variation. — (See Variation r 
Angle of.) 

Angle, Plane An angle contained 

between two straight lines. 

Angle, Solid An angle contained 

between two surfaces. 

Angle, Supplement of What an 

angle needs to make its value 180 degrees, or 
two right angles. 

Thus in Fig. 13, E A C, is the supplement of 
E A D, because EAD-(-EAC = i8o degrees, 
or two right angles. 

Angle, Unit An angle of 57.29578° 

or 57° 17' 44.8' nearly. — (See Velocity, An- 
gular) 

Angular Currents. — (See Currents, An- 
gular) 

Angular Telocity. — (See Velocity, Angu- 
lar) 

Animal Electricity. — (See Electricity, 
Animal) 

Animal Magnetism. — ^Sse Magnetism, 
Animal) 

Anion. — The electro-negative radical of a 
molecule. 

Literally, the term ion signifies a group of 
wandering atoms. Ai anion is that group of 
atoms of an electrically decomposed or electrolyzed 



Ani.] 



22 



[Alll!, 



mol.cule which appears at the anode. (See 
Electrolysis. Anode.) 

As the anode is connected with the electro- 
positive terminal of a source, the anion is the 
electro-negative radical or group of atoms, and 
therefore appears at the electro-positive terminal. 

Akathion, or electro- positive radical, ap_ ears 
at the kathode, which is connected with the 
electro negative terminal of the battery. Oxygen 
and chlorine are anions. Hydrogen and the 
metals are kathions. 

Anisotropic Conductor. — (See Conductor, 
Anisotropic}) 

Anisotropic Medium. — (See Medium, 
Anisotropic}) 

Annealing, Electric — 



— A process 
for annealing metals in which electric heating 
is substituted for ordinary heating. 

Annual Inequality of Earth's Magnet- 
ism. — (See Inequality, Annual, of Earth's 
Magnetism. 

Annual Variation of Magnetic Needle. 
— (See Needle, Magnetic, Annual Variation 
of.) 

Annunciator, Burglar- Alarm An 

annunciator used in connection with a system 
of burglar-alarms. (See Alarm, Burglar}) 

Annunciator Clock, Electric — 

(See Clock, Electric Annu?iciator}) 

Annunciator Drop. — (See Drop, Annun- 
ciator}) 

Annunciator Drop, Automatic 

(See Drop, Automatic Annunciator) 

Annunciator, Electro-Magnetic 

An electric device for automatically indicating 
the points or places at which one or more 
electric contacts have been closed. 

The character of the annunciator depends, of 
course, on the character of the places at which 
these points, places or stations are situated. 

Annunciators are employed for a variety of 
purposes. In hotels they are used for indicating 
the number of a room the occupant of which 
desires some service, which he signifies by push- 
ing a button, thus closing an electric circuit. 
This is indicated or announced on the annuncia- 
tor by the falling of a drop, on which is printed a 
number corresponding with the room, and by the 



ringing of a bell to notify the attendant. The num- 
ber is released by the movement of the armature 
of an electro-magnet. The drops are replaced in 
their former position by some mechanical device 
operated by the hand. In the place of a drop a 



wsm 




Fig. 14. Electro -Magnetic Annunciator. 

needle is sometimes u ed, which, by the attraction 
of the armature of an electro-magnet, points to 
the number signaling. 

Annunciators for houses, burglar-alarms, fire- 
alarms, elevators, etc., are 
of the same general con- 
struction. 

Annunciators are general- 
ly operated by electro-mag- 
netic attraction or repulsion, 
and are therefore some- 
times called electro -magnetic 
annunciators. 

Fig. 14 shows an annun- 
ciator suitable for use in 
hotels. 

The numbers 28 and 85 
are represented as having 
been dropped by the closing 
of the circuit connected 
with them. 

Annunciator, Eleva- 
tor An annuncia- 
tor connected with an 




Fig. rf. Elevator 
Annunciator. 



elevator to indicate the 
floor signaling. 
One form of elevator annunciator is shown in 
Fig. 15. 



Anil.] 



23 



[Ann, 



Annunciator, Fire-Alarm An 

annunciator used in connection with a system 
of fire-alarms. 

Annunciator, Gravity-Drop — An 

annunciator whose signals are operated by 
the fall of a drop. 




Fig. lb. Gravity-Drop Annunciator. 

A form of gravity-drop annunciator is shown 
in Fig. 16. The armature mechanism for the 
release of the drop will be understood by an in- 
spection of the drawing. 

Annunciator, Hotel An annun- 
ciator connected with the different rooms of a 
hotel. 

A hotel-annunciator is generally provided with 
a return bell and guest-call. 

Annunciator, House An annun- 
ciator connected with the rooms of a house. 

Annunciator, Needle An annun- 
ciator, the indications of which are given by 
the movements of a needle instead of the fall 
of a drop. 

A form of needle-annunciator is shown in 
Fig. 17. 

Annunciator, Oral or Speaking Tube 

An annunciator electrically operated 



by means of a puff of breath transmitted 
through an ordinary speaking tube. 

The oral-annunciator is a contr.vance whereby 
a central office is placed in communication with a 
number of speaking tiuxs coming from different 
points in a hotel or other place. A person 
in any room, who wishes to communicate 
with the central office, blows through the 
speaking tube in his room, and thus, by 
effecting an electric contact, rings a bell and 
operates a drop at the annunciator, thus indicat- 
ing the exact tube at which the attendant is to 
receive the message. The attendant can thus be 
placed in easy communicatio 1 with each of the 
rooms whose speaking tubes connect with the 
annunciator. 

Annunciator, Pendulum or Swinging- 

— An annunciator, the indicating arm of 
which consists of a pendulous, or swinging arm, 




Fig. 17. Needle- Annunciator. 

which, when at rest, points vertically down- 
ward, and which is moved to the right or left 
by the action of the current. 

Pendulous, or swinging-annunciators are gen- 
erally so arranged as to need no replacement. 



Auo.J 



24 



[App. 



On the cessation of the current the indicator arm 
drops vertically downward. 

A relay is preferably used with pendulum- 
annunciators, since the rapid makes and breaks 
of the current by the bell alarm interlere with 
their satisfactory action. 

Anodal. — Pertaining to the anode. (See 
Anode :) 

Anodal Diffusion. — (See Diffusion, Ano- 
dal^) 

Anode. — The conductor or plate of a de- 
composition cell connected with the positive 
terminal of a battery, or other electric source. 

That terminal of an electric source out of 
which the current, flows into the liquid of a 
decomposition cell or voltameter is called the 
anode. 

That terminal of an electric source into 
which the current flows from a decomposition 
cell or voltameter is called the kathode. 

The anode is connected with the carbon or 
positive terminal of a voltaic battery, and the 
kathode with the zinc, or negative terminal. 
Therefore the word anode has been used to 
signify the positive terminal of an electric source, 
and kathode, the negative terminal, and in this 
sense is employed generally in electro-thera- 
peutics. It is preferable, however, to restrict the 
use of the words anode and kathode to those 
terminals of a source at which electrolysis is 
taking place. 

The terms anode and kathode in reality refer 
to the electro-receptive devices through which 
the current flows. S.nce it is assumed that the 
current flows out of a source from its positive 
pole or terminal, and back through the source at 
its negative pole or terminal, the pole of any 
device which is connected with the positive pole 
of a source is the part or place at which the 
current enters and flows through it, and that 
connected with the negative pole, the part at 
which it leaves. Hence, probably, the change 
in the use of the words already referred to. 

Since the anion, or the electro negative radical, 
appears at the anode, it is the anode of an electro- 
plating bath, or the plate connected wiih the 
positive terminal of the source, that is dissolved. 

When the term anode was first proposed by 
Faraday, voltaic batteries were the only available 
electric source, and the term referred only to the 



positive terminal of a voltaic battery when 
placed in an electrolyte. 

Anodic. — Pertaining to the anode. (See 
Anode.) 

Anodic Electro-Diagnostic Reactions. — 

(See Reactions, Kathodic and Anodic Elec- 
tro-Diagnostic) 

Anodic Opening Contraction. — (See Con- 
tration, Anodic Opening) 

Anomalous Magnet. — (See Magnet, An- 
omalous) 

Anomalous Magnetization. — (See Mag- 
netization, Anojnalous) 

Anti-Induction Cable (See Cable, 

Anti-Induction) 

Anti-Induction Couductor. — (See Con- 
ductor, Anti-Induction) 

Antilogous Pole. — (See Pole, Antilogous) 

Anvil. — The front contact of a telegraphic 
key that limits its motion in one direction. 
(See Key, Telegraphic) 

Aperiodic Galvanometer. — (See Galva- 
nometer, Aperiodic) 

Apparatus, Faradic-Induction — 

An induction coil apparatus for producing 
faradic currents. 

A voltaic battery is connected with the primary 
of an induction coil, and its current rapidly 
broken by an automatic break, or by a hand 
break. The alternating or faradic currents thus 
produced in the secondary coils are used for 
electro- therapeutic purposes. (See Coil, Induc- 
tion) 

Faradic induction apparatus is made in a great 
variety of forms. They all operate, however, on 
essentially the same principles. 

Apparatus, Faradic, Magneto-Electric 

A small magneto-electric machine 

employed in electro-therapeutics for producing 
faradic currents. 

Magneto-electric faradic machines consist essen- 
tially of a coil of wire wrapped on an armature 
core that is rotated before the poles of permanent 
magnets. No commutator is employed, since it is 
desired to obtain rapidly alternating currents. 

Apparatus, Interlocking Devices 

for mechanically operating from a distant signal 



App.] 



25 



[Arc. 



tower, railroad switches and semaphore signals 
for indicating the position of such switches, 
by means of a system of interlocking levers, 
so constructed that the signals and the 
switches are so interlocked as to render it 
impossible, after a route has once been set up 
and a signal given, to clear a signal for a 
route that would conflict with the one previ- 
ously set up. (See Block System for Rail- 
roads?) 

Apparatus, Magneto-Electric Medical 
A term applied to small magneto- 
electric machines employed in medical elec- 
tricity for the production of uncommuted 
or faradic currents. (See Apparatus, Fara- 
dic, Magneto-Electric?) 

Apparatus, Registering-, Electric 

Devices for obtaining permanent records by 
electrical means. 

Apparatus, Registering, Telegraphic 

— A name sometimes given to a telegraphic 
recorder. (See Recorder, Chemical, Bain's. 
Recorder, Morse. Recorder, Siphon?) 

Apparent Co-efficient of Induction. — 

(See Induction, Apparent Co-efficient of) 

Arago's Disc. — (See Disc, Arago's) 

Arc. — A voltaic arc. (See Arc, Voltaic) 

Arc. — To form a voltaic arc. 

A dynamo-electric machine is said to arc at the 
commutator, when the current passes as visible 
sparks across the spaces between adjacent seg- 
ments. 

This action at the commutator is more gener- 
ally called sparking or burning. 

Arc, Alternating A voltaic arc 

formed by means of an alternating current. 

In order to avoid the extinction of the arc a 
certain number of alternations per second is nec- 
essary. The alternating arc produces a loud 
singing noise. At very high frequencies, how- 
ever, the noise disappears. 

The alternating arc, not possessing a fixed posi- 
tive crater, requires to be covered by a good 
reflector to throw the light downward. 

Arc, Ampere A single conductor 

bent in an arc of a circle, and used in electric 
balances for measuring the electric current. 



Arc Blow-Pipe. — (See Blow-Pipe, Elec- 
tric Arc.) 

Arc, Compound An arc formed 

between more than two eparate electrodes. 

Arc, Counter Electromotive Force of 

An electromotive force generally be- 
lieved to be set up on the formation of a 
voltaic arc, opposed in direction to the electro- 
motive force maintaining the arc. (See Force, 
Electro?notive, Counter?) 

This counter electromotive force is believed to 
have its origin partly in the energy absorbed at 
the crater of the positive carbon, where the car- 
bon is volatilized, and given out at the nipple on 
the negative carbon, where it is deposited or 
solidified. It is to be noted in this connection 
that the apparent resistance of the carbon voltaic 
arc is not directly proportional to the length of 
the arc. 

Arc, Electric A term sometimes 

used for the voltaic arc. (See Arc, Voltaic?) 

Arc, Frying of A frying sound at- 
tending the formation of a voltaic arc when 
the carbons are too near together. 

The cause of the frying sound is probably the 
same as that of hissing. (See Arc, Hissing of .) 

Arc, Hissing of A hissing sound 

attending the formation of voltaic arcs when 
the carbons are too near together. 

The cause of the hissing is not entirely under- 
stood. Prof. Elihu Thomson suggests that it is 
due to a too rapid volatilization of the carbons. 

Arc Lamp.— (See Lamp, Arc.) 

Arc Lamp, Electric -(See Lamp, 

Electric Arc) 
Arc Lamp, Triple Carbon Electric 

— (See Lamp, Arc, Triple Carbon Electric) 
Arc Lighting. — (See Lighting, Arc) 

Arc, Metallic A voltaic arc formed 

between metallic electrodes. 

When the voltaic arc is formed between metallic 
electrodes instead of carbon electrodes, a flaming 
arc is obtained, the color of which is characteristic 
of the burning metal ; thus copper forms a brill- 
iant green arc. The metallic arc, as a rule is 
much longer than an arc with the same current 
taken between carbon electrodes. 

Arc Micrometer. — (See Microineter, Arc) 



Arc] 



26 



[Are.* 



Arc, Noisy 



-A voltaic arc, the 



maintenance of which is attended by frying, 
hissing, or spluttering sounds. 

Arc, Quiet A voltaic arc which is 

maintained without sensible sounds. 

Arc, Roaring of A roaring sound 

attending the formation of a voltaic arc when 
the carbons are too near together and a very 
powerful current is used. 

Arc, Simple An arc formed be- 
tween two electrodes. 

Arc, Spluttering 1 of A spluttering 

sound attending the formation of a voltaic 
arc. 

Prof. Elihu Thomson suggests that the cause of 
spluttering is due to the presence of impurities in 
the carbons, or from the sudden evolution of gas 
from insufficiently baked carbons. 

Arc, Yoltaic The brilliant arc or 

bow of light which appears between the elec- 
trodes or terminals, generally of carbon, of a 
sufficiently powerful source of electricity, when 
separated a short distance from each other. 

The source of light of the electric arc lamp. 

It is called the voltaic arc because it was first 
obtained by the use of the battery invented by 
Volta. The term arc was given to it from the 
shape of the luminous bow or arc formed between 
the carbons. 

To form the voltaic arc the carbon electrodes 
are first placed in contact and then gradually 
separated. A brilliant arc of flame is formed be- 
tween them, which consists mainly of volatilized 
carbon. The electrodes are consumed, first, by 
actual combination with the oxygen of the air; 
and, second, by volatilization under the combined 
influence of the electric current and the intense 
heat. 

As a result of the formation of the arc, a crater 
is formed at the end of the positive carbon, and 
appears to mark the point out of which the 
greater part of the current flows. 

The crater is due to the greater volatilization 
of the electrode at this point than elsewhere. 
It marks the position of highest temperature of the 
electrodes, and is the main source of the light of 
the arc. When, therefore, the voltaic arc is em- 
ployed for the purposes of illumination with 
vertically opposed carbons, the positive carbon 
should be made the upper carbon, so that the 



focus of greatest intensity of the light may be- 
favorably situated for illumination of the space 
below the lamp. When, however, it is desired to 
illumine the side of a building above an arc lamp, 
the lower carbon should be made positive. 

The positive carbon is consumed about twice as. 
rapidly as the negative, both because the negative 
oxygen attacks the points of the positive carbon, 
and because the positive carbon suffers the most 
rapid volatilization. 

The electric current passes through the space 
occupied by the voltaic arc because — 

(I.) The heated arc is a partial conductor of 
electricity. 

(2.) Because small charges of electricity are 
carried bodily forward from the positive to the 
negative carbon through the space of the voltaic 
arc, by means of the minute particles which are 
volatilized at the positive electrode. 

S. P. Thompson has shown that the tempera- 
ture of the light-emitting surface of the carbon is- 
the temperature of the volatilization of carbon, 
and is therefore constant. 

Dr. Fleming found that " A rise of potential 
along the arc takes 
place very suddenly, 
just in the neighbor- 
hood of the crater." 

The crater in the 
end of the positive car- 
bon is seen in Fig. 18.. 
On the opposed end 
of the negative carbon 
a projection or nipple 
is formed by the de- 
posit of the electrical- 
ly volatilized carbon. 
Fig. 18. Voltaic Arc. The rounded masses 
or globules that appear on the surface of the elec- 
trodes are due to deposits of molten foreign mat- 
ters in the carbon. 

The carbon, both of the crater and its opposed 
nipple, is converted into pure, soft graphite. 

Arc, Yoltaic, Resistance of The 

resistance offered by the voltaic arc to the 
passage of the current. 

As in all other conductors, the ohmic resistance 
of the arc increases with its length, and decreases 
with its area of cross- section. The apparent 
resistance, however, is not directly proportional 
to the length. An increase of temperature de- 
creases the lesistance of the voltaic arc. 




Arc] 



27 



[Arm, 



The total apparent resistance of the voltaic arc 
is composed of two parts, viz. : 

(i.) The true ohmic resistance. (See Resist- 
ance, Ohmic.) 

(2.) The counter electromotive force, or spuri- 
ous resistance. (See Resistance, Spurious.) 

Arc, Watt A voltaic arc, the elec- 
tric power of which is equal to a given number 
of watts. 

The ordinary long-arc, as employed in arc 
lighting, has a difference of potential of about 45 
volts and a current strength of about 10 amperes. 
It is, therefore, a 450-watt arc. 

Arch, Auroral The archlike form 

sometimes assumed by the auroral light. (See 
Aurora Borealis.) 

Arcing'. — Discharging by means of voltaic 
arcs. (See Arc, Voltaic.) 

Arcing at the commutator of a dynamo-electric 
machine not only prevents the proper operation 
of the machine, but eventually leads to the de- 
struction of the brushes and the commutator. 

Areometer, Bead A form of are- 
ometer suitable for rapidly testing the density 
of the liquid in a storage cell. 

The bead aieometer consists of a glass tube, 
open at both top and bottom, containing a few 
glass beads, so weighted as to float at liquid 
densities such as 1. 105, 1.170, 1.190 
and 1.200. To use the instrument, 
it is immersed in the liquid of the 
storage cell, and then withdrawn. 
The finger being kept in the upper 
opening, the liquid does not escape 
through the small opening at the 
bottom. The density is then ascer- 
tained by noting the beads that 
float. 

Areometer or Hydrometer. 

— An instrument for determin- 
ing the specific gravity of a liquid. 
A common form of hydrometer 
consists, as shown in Fig. 19, of a 
closed glass tube, provided with a 
bulb, and filled at the lower end 
with mercury or shot, so as to in- 
sure its vertical position when Fig. ig. Hy- 
floating in a liquid. When placed drometer. 
in different liquids, it floats with part of the tube 
out of the liquid. The lighter the liquid, the 



smaller is the portion that remains out of the 
liquid when the instrument floats. The specific 
gravity is determined by observing the depth to 
which the instrument sinks when placed in different 
liquids, as compared with the depth it sinks when 
placed in water. 

Areometry. — The measurement of specific 
gravity by means of an areometer. 

Argand Burner, Electric Hand-Lig-hter 

(See Burner, Argand, Electric Hand- 
Lighter^) 

Argand Burner, Electric Plain-Pendant 

(See Bur7ier, Plain Pendant, Argand, 

Electric) 

Argand Burner, Electric Ratchet-Pen- 
dant (See Burner, Ratchet-Pendant, 

Argand, Electric.) 

Arg-yrometry.— The art of determining 
the weight of electrolytically deposited silver. 
(See Balance, Plating) 

Arm, Balance One of the resist- 
ances of an electric balance. (See Arms, 
Bridge or Balance. Bridge, Electric?) 

Arm, Bridg-e A bridge arm. (See 

Arms, Bridge or Balance.) 

Arm, Cross A horizontal beam at- 
tached to a pole for the support of the in- 
sulators for telegraph, electric light or other 
electric wires. 

A telegraphic arm. (See Arm, Tele- 
graphic.) 

Arm, Kocker An arm on which the 

brushes of a dynamo or motor are mounted 
for the purpose of shifting their position on 
the commutator. 

Arm, Semaphore The movable 

arm of the signal apparatus employed in block 
systems for railroads, for the purpose of in- 
forming engineers of trains of the condition 
of the road as regards other trains. 

In the absolute block system, as used on some 
roads, there are two positions for the semaphore 
arm, viz.: 

(I.) For Danger — when in a horizontal position, 
or at 90 degrees with the vertical supporting pole. 

(2.) Clear — when dropped below the horizontal 
position through an angle of 75 degrees. 

In the Permissive Block System, a third position 



Arm.] 



28 



[Arm, 



intermediate between the 1st and the 2d, or at an 
angle of 37 degrees 30 minutes with the horizontal 
position, is used for caution. (See Block System 
for Railroads.) 



Armature, Bi-polar 



-An armature 



Arm, Signal 



-A semaphore arm. 



(See Arm, Semaphored) 

Arm, Telegraphic A cross-arm 

placed on a telegraphic pole for the support 
of the insulators. 

These arms are generally called cross-arms. 

Armature. — A mass of iron or other 
magnetizable material placed on or near the 
pole or poles of a magnet. 

In the case of a permanent magnet, the arma- 
ture, when used as a keeper, is of soft iron and is 
placed directly on the magnet poles. In this case 
it preserves or keeps the magnetism by closing 
the lines of magnetic J 'orce of the magnet through 
the soft iron of the armature, and is then called a 
keeper. (See Force, Magnetic, Lines of.) 

In the case of an electro-magnet, the armature 
is placed near the poles, and is moved toward 
them whenever the magnet is energized by the 
passage of the current through the magnetizing 
coils. This movement is made against the action 
of a spring or weights, so that on the loss of 
magnetism by the magnet, the armature moves 
from the magnet poles. (See Magnet, Permanent. 
Afagnet, Keeper of. ) 

When the armature is of soft iron it moves to- 
ward the magnet on the completion of the circuit 
through its coils, no matter in what direction 
the current flows, and is then called a non-polar- 
ized armature. (See Armature, Non-Poiarized. ) 

When made of steel, or of another electro-mag- 




Fig. 20. Bi-polar Armature. 

net, it moves from or toward the poles, accord- 
ing to whether the poles of the armature are of 
the same or of a different polarity from those of 
the magnet. Such an armature is called a 
polarized armature. (See Armature, Polarized.) 



of a dynamo-electric machine the polarity of 
which is reversed twice in every revolution 
through the field of the machine. 

A form of bi-polar armature is shown in Fig. 20. 
The word bi-polar armature is not generally 
employed. The term applies rather to the field- 
magnet poles than to the armature. 

Armature Bore. — (See Bore, Armature?) 

Armature Bore, Elliptical — (See 

Bore, Elliptical Armature?) 

Armature Chamber. — (See Chamber, 
Armature?) 

Armature Coils, Dynamo — (See 

Coils, Armature, of Dynamo-Electric Ma- 
chine?) 

Armature Core, Dynamo — (See 

Core, Armature, of Dy7iamo-Electric Ma- 
chine?) 

Armature, Cylindrical A term 

sometimes applied to a drum armature. 
(See Armature, Drum. Armature, Dy- 
namo-Electric Machine.) 

Armature, Cylindrical Ring. — A ring 
armature with a core in the shape of a com- 
paratively long cylinder. 

Armature, Disc An armature of a 

dynamo-electric machine, in which the arma- 
ture coils consist of flat coils, supported on 
the surface of a disc. (See Armature, Dy- 
namo-Electric Machine?) 

Armature, Dissymmetrical Induction of 

Any induction produced in the arma- 
ture of a dynamo-electric machine that is un- 
equal in amount on opposite halves, or in sym- 
metrically disposed portions of the armature. 

Dissymmetrical induction in the armature may 
cause annoying or injurious sparking at the com- 
mutator. It may arise — 

(1 ) From a lack of symmetry in the amount of 
the armature windings. 

(2.) From a lack of symmetry in the arrange- 
ment of the armature windings on the armature 
core. 

(3. ) From a lack of symmetry of the pole pieces 
of the machine. 

(4.) From an improper position of the brushes 



Arm.] 



29 



[Arm, 



as regards the neutral point on the commutator, 
-causing a temporary short-circuiting of one or 
more of the armature coils. 

Armature, Drum An armature of 

a dynamo-electric machine, in which the 
armature coils are wound longitudinally over 
the surface of a cylinder or drum. (See 
Armature, Dynamo- Electric Machined) 

A form of drum -armature is shown in Fig. 21. 




•Fig. 21. Drum- Armature. 

Armature, Dynamo-Electric Machine 

The coils of insulated wire together 

with the iron armature core, on or around 
which the coils are wound. 

That part of a dynamo-electric machine in 
which the differences of potential which 
•cause the useful currents are generated. 

Generally, that portion of a dynamo-elec- 
tric machine which is revolved between the 
pole pieces of the field magnets. 

The armature of a dynamo-electric machine 
usually consists of a series of coils of insulated 
wire or conductors, wrapped around or grouped 
on a central core of iron. The movement of 
these wires or conductors through the magnetic 
field of the machine produces an electtic cur- 
rent by means of the electromotive forces so gen- 
erated. Sometimes the field is rotated ; some- 
times both armature and field rotate. 

The armatures of dynamo-electric machines 
are of a great variety of forms. They may for 
•convenience be arranged under the following 
heads, viz.: 

Cylindrical or drum-armatures, disc -arma- 
tures, pole-or-radial armatures, ring armatures, 
and spherical-armatures . For further particulars 
see above terms. Armatures are also divided 



into classes according to the character of the 
magnetic field through which they move — viz.: 
unipolar, bipolar, and multipolar armatures. 

The English sometimes use the word cylindrical 
armature as a synonym of ring-armature. 

A unipolar-armature is one whose polarity is 
never reversed. A bipolar-armature is one in 
which the polarity is reversed twice in every 
rotation; multipolar armatures have their po- 
larity reversed a number of times in every rota- 
tion. 

The term armature as applied to a dynamo- 
electric machine was derived from the fact that 
the iron core acts to magnetically connect the 
two poles of the field magnets in the same 
manner that an ordinary armature connects the 
poles of a magnet. 

Armature, Flat King A ring-arma- 
ture with a core in the shape of a short cylin- 
drical ring. 

Armature, Girder An armature 

with an H-shaped or girder-like core. 
An H-shaped armature. 

Armature, Intensity An old term 

for an armature with coils of many turns and 
of a comparatively high resistance. 

Armature, Lamination of Core of 

— A division of the iron core of the armature 
of a dynamo-electric machine or motor, so as 
to avoid the formation of eddy-currents 
therein. (See Core, Lamination of. Cur- 
rents, Eddy.) 

Armature, Multipolar A dynamo- 
electric machine armature whose polarity is 
reversed more than twice during each rotation 
in the field of the machine. 

Armature, Neutral A non-polarized 

armature. (See Armature, Non-Polarized?) 

Armature, Neutral-Relay A relay 

armature, consisting of a piece of soft iron, 
which closes a local circuit whenever its elec- 
tro-magnet receives an impulse over the main 
line. (.See Armature, Polarized?) 

This term is applied in contradistinction to a 
polarized relay armature. 

Armature, Non-Polarized — An 

armature of soft iron, which is attracted toward 
the poles of an electro-magnet on the comple- 



Arm.] 



30 



[Arm. 



tion of the circuit, no matter in what direc- 
tion the current passes through the coils. 

The term non-polarized is ustd in contradistinc- 
tion to polarized armature. "(See Armature, 
Polarized. ) 

Th non-polarized armature of a relay magnet 
is generally called the neutral-relay armature. 

Armature of a Cable, or Cable- Armature. 

— A term sometimes employed for the sheath- 
ing or protecting coat of a cable. 

The term armor sheathing or coating is prefer- 
able. 

Armature of a Condenser, or Condenser 
Armature. — A term sometimes applied to 
the metallic plates of a condenser or Leyden 
jar. 

The use of this term is unnecessary and ill- 
advised. The term coating or plate would appear 
to be preferable. 

Armature of Holtz Machine, or Holtz- 
Machine Armature. — The pieces of paper 
that are placed on the stationary plate of the 
Holtz and other similar electrostatic induction 
machines. 

Armature Pockets. — (See Pockets, Ar7na- 
ture.) 

Armature, Polarized An armature 

which possesses a polarity independent of 
that imparted by the magnet pole near which 
it is placed. 

In permanent magnets the armatures are made 
of soft iron, and therefore, by induction, become 
of a polarity opposite to that of the magnet poles 
that lie nearest them. They have, therefore, only 
a motion of atraction toward such poles. (See 
Induction, Magnetic. ) 

In electro-magnets the armatures may either be 
made of soft iron, in which case they are attracted 
only on the passage of the current; or they may 
be formed of permanent steel magnets, or may be 
electro-magnets themsehes, in which case the pas- 
sage of the current through the coils of the elec- 
tro-magnet, or electro-magnets, may cause either 
attraction or repulsion, according as the adjacent 
poles are of opposite polarity or are of the same 
polarity. 

Armature, Pole An armature the 

coils of which are wound on separate poles 



that project radially from the periphery of a 
disc, drum or ring. 
A pole-armature showing the arrangement of 




Fig. 22. Pole- Armature. 
the coils and their connection to the commutator 
segments is seen in Fig. 22. 

Armature, Quantity An old term 

for an armature wound with but a few coils 
of comparatively low resistance. 

Armature, Radial -. A term some- 
times used instead of pole-armature. (See 
Armature, Pole) 

Armature, Ring A dynamo-electric 

machine armature, the coils of which are 
wound on a ring-shaped core. 




Fig. 23. Ring- Armature. 
A ring-armature is shown in Fig. 23, together 
with the disposition of the coils and their connec- 
tion to the segments of the commutator. 

Armature, Shuttle A variety of 

drum armature in which a single coil of 
wire is wound in an H -shaped groove formed 
in a bobbin shaped core. 

The old form of Siemens-armature. 

Armature, Single-Loop A closed 

conducting circuit consisting of a single loop, 
capable of revolving in a magnetic field so as 
to cut its lines of force. 

Armature, Spider. — (See Spider, Arma- 
ture) 



Arm. J 



31 



[Arr. 



-A dynamo- 



Armature, Spherical — 

electric machine armature, the coils of which 
are wound on a spherical iron core. 

The Thomson -Houston dynamo, which is the 
only machine employing an armature of this type, 
has its armature formed by wrapping three coils 
of insulated wire on a core of iron so shaped as 
to insure an approximately spherical armature 
when wrapped. 

Armature, Toothed-Ring An ar- 
mature, the core of which is in the shape of 
a ring, provided with a number of teeth in the 
spaces between which the armature coils are 
placed. 

Armature, Unipolar A dynamo- 
electric machine armature whose polarity is 
not reversed during its rotation in the field 
of the machine. 

Armature, Yentilation of A pro- 
cess for insuring the free passage of air 
through the armature of a dynamo-electric 
machine in order to prevent overheating. 

Armor of Cable. — (See Cable, Armor of) 

Armored Cable. — (See Cable, Armored) 

Armored Conductor.— (See Conductor, 
Armored) 

Arms, Bridge or Balance The 

electric resistances, in the electric balance or 
bridge. (See Bridge, Electric) 




Zn e 
Fig. 24. Arms of Balance. 

An unknown resistance, such, for example, as 
D, Fig. 24, is measured by proportioning the 
known resistances, A, C and B, so that no current 
flows through the galvanometer G, across the 
circuit or bridge M G N. 

Arms, Proportionate The two re- 
sistances or arms of an electric bridge whose 
relative or proportionate resistances only are 
required to be known in order to determine, 



in connection with a known resistance, the 
value of an unknown resistance placed in the 
remaining arm of the bridge. 

Thus is Fig. 24, A and B, are the proportionate 
arms. 

Arrangement or Device, Electromotive 

A term sometimes employed to rep- 
resent a dynamo-electric machine, voltaic cell 
or other electric source, by means of which 
electromotive force can be produced. 

Electric sources do not produce electric Cur- 
rents, but differences of potential or electro- 
motive force. Electric sources are therefore very 
properly termed electromotive devices. 

Arrester, Lightning A device by 

means of which the apparatus placed in any- 
electric circuit is protected from the destruc- 
tive effects of a flash or bolt of lightning. 

In the phenomena of lateral induction and 1 
alternative path, we have seen the tendency of a. 
disruptive discharge to take a short-cut across an 
intervening air space, rather than through a. 
longer though better conducting path. Most 
lightning arresters are dependent for their opera- 
tion on this tendency to lateral discharge. (See 
Induction, Lateral. Path, Alternative.) 

A form of lightning arrester is shown in Fig. 25. 




Fig. 23. Comb Lightning-Arrester. 

The line wires, A and B, are connected by two 
metallic plates to C and D, respectively. 

These plates are provided with points, as shown y 
and placed near a third plate, connected to the 
ground by the wire G. Should a bolt strike the 
hne, it is discharged to the earth through the 
wire G. 

Various forms are given to lightning arresters, 
of this type. The projections are sometimes placed 
on the ground -connected plate as well as on the 
plates connected to line wires. This form is* 
sometimes called a comb arrester, or pro'ecto*. 



Arr.] 



32 



fAst, 



Arrester, Lightning, Comb — A 

term sometimes applied to a lightning ar- 
rester in which both the line and ground 
plates are furnished with a series of teeth, 
like those on a comb. (See Arrester, Light- 
ning^ 

Arrester, Lightning, Counter-Electro- 
motive Force A lightning arrester, 

in which the passage of the discharge through 
the instruments to be protected is opposed 
by a counter-electromotive force, generated 
"by induction on the passage of the discharge 
of the bolt to earth. 

The counter-electromotive force lightning ar- 
rester is an invention of Professor Elihu Thomson. 

It assumes a variety of forms. In the shape 
shown in Fig. 26, the line circuit of the dynamo, 




F.'g. 26. Counter- Electromotive Force Lightning 
Arrester. 

D, has one end connected to ground, and the 
other end has two conducting paths to ground. 
One of these paths is through the ordinary comb- 
protector at P, by the ground plate E; this cir- 
cuit includes a few turns 
of wire C. The other 
path is through a corres- 
ponding coil C, either 
interior or exterior to C, 
so as to be within its in- 
ductive field. As will be 
seen from the figure, C, is 
Fig. 27. Counter-Eiec. connected through the 
tromotive Force Light- machine to the ground. 
ning Arrester. The induction coils C 

and C, are thoroughly insulated from each 
other. 

Should a lightning flash or other static discharge 
pass through the circuit C, which is of compara- 
tively low self-induction, a counter-electromoiive 
force is produced in the other coil C, which 
protects the line circuit. 




In the form of lightning arrester shown in 
Fig. 27, the coil in the path of the direct light- 
ning discharge is formed into an exterior mesh or 
net work surrounding the dynamo to be pro- 
tected. In this case, the coils of the dynamo act 
as the secondary coils in which the counter elec- 
tromotive force is set up. 

Arrester, Lightning, Transformer 

— A form of lightning arrester designed for 
the protection of transformers. 

The Thomson arrester for transformers oper- 
ates on the same principle as his arc-line pro- 
tector. In the latter the arc, when formed, 
is blown out by the action of the field of an 
electro-magnet. This arc is formed on curved 
metallic bows, one of which is connected to line 
and the other to earth. The arc is formed at the 
smallest interval between the bows, and is extin- 
guished by being driven by action of a magnetic 
field toward greatest interval. 

Arrester Plate of Lightning Protector. — 

(See Plate, Arrester, of Lightning Pro- 
tectory 
Arrester Plates. — (See Plates, Arrester?) 

Articulate Speech. — (See Speech, Articu- 
lated) 

Artificial Carbons. — (See Carbons, Arti- 
ficial) 

Artificial Illumination. — (See Illumina- 
tion, Artificial.) 

Artificial Line.— (See Line, Artificial) 

Artificial Magnet. — (See Magnet, Arti- 
ficial) 

Asphyxia. — Suspended respiration, result- 
ing eventually in death, from non-aeration of 
the blood. 

In cases of insensibility by an electric shock a 
species of asphyxia is sometimes brought about. 
This is due, probably, to the failure of the nerves 
and muscles that carry on respiration. The exact 
manner in which death by electrical shock results 
is not known. (See Death, Electric) 

Assymmetrical Resistance. — (See Resist- 
ance, Assym?netrical) 

Astatic. — Possessing no directive power. 

Usually applied to a magnetic or electro-mag- 
netic device which is free from any tendency to 
take a definite position on account of the earth's 
magnetism. 



Ast. 



b'd 



[Ato. 



Astatic Circuit.— (See Circuit, Asiatic) 
Astatic Couple. — See Couple, Astatic?) 
Astatic Galvanometer.— (See Galvanom- 
eter, Astatic.) 

Astatic Needle. — (See Needle, Astatic.) 

Astatic Pair. — (See Pair, Astatic.) 

Astatic System. — (See System, Astatic) 

Astronomical Meridian. — (See Meridian, 
Astronomical?) 

Asymptote of Curve. — (See Curve, Asymp- 
tote of) 

Atmosphere, An A unit of gas or 

fluid pressure equal to about 1 5 pounds to the 
square inch. 

At the level of the sea the atmosphere exerts a 
pressure of about 15 pounds avoirdupois, or, 
more accurately, 14.73 pounds, on every square 
inch of the earth's surface. This value has there- 
fore been taken as a unit of fluid pressure. 

For more accurate measurements pounds to the 
square inch are employed. 

In the metric system of weights and measures 
an atmosphere is considered equal to 1,033 
grammes per square centimetre. 

Atmospheric pressures are measured by instru- 
ments called Manometers. (See Manometer.) 

Atmosphere, Residual The traces 

of air or other gas remaining in a space which 
has been exhausted of its gaseous contents 
by a pump or other means. 

It is next to impossible to remove all traces of 
air from a vessel by any known form of pump or 
other appliance. (See Vacuum, Absolute.) 

Atmosphere, The The ocean of 

air which surrounds the earth. 

The atmosphere is, approximately, composed, 
by weight, of oxygen 23 parts, and nitrogen 77 
parts. Besides these there are from 4 to 6 parts 
in 10,000 of carbonic acid gas (or about a cubic 
inch of carbonic acid to a cubic foot of air), and 
varying proportions of the vapor of water. 

1 he oxygen, nitrogen and carbonic acid form 
the constant ingredients of the atmosphere, the 
vapor of water the variable ingredient. There 
are in most localities a number ot other variable 
ingredients present as impurities. 

Atmospheric Electricity. — (See Electric- 
ity, Atjnospheric) 



Atmospheric Electricity, Origin of 

— (See Electricity, Atmospheric, Origin of) 

Atom. — The smallest quantity of elemen- 
tary or simple matter that can exist. 
An ultimate particle of matter. 

Atom means that which cannot be cut. It is 
generally believed that material atoms are abso- 
lutely unalterable in size, shape, weight and den- 
sity ; that they can neither be cut, scratched, 
flattened, nor distorted ; and that they are un- 
affected in size, density, or shape, by heat or 
cold, or by any known physical force. 

Although almost inconceivably small, atoms 
nevertheless possess a definite size and mass. 
According to Sir William Thomson, the smallest 
visible organic particle, 1-4000 of a millimetre in 
diameter, will contain about 30,000,000 atoms. 

Atom, Closed-Magnetic Circuit of 

(See Circuit, Closed-Magnetic, of Atom) 

Atom, Gramme — Such a number 

of grammes of any elementary substance as is 
numerically equal to the atomic weight of 
the substance. 

The gramme-atom of a substance represents 
the number of calories required to raise the tem- 
perature of one gramme ot that substance through 
1 degree C. (See Heat, Atomic. Calorie.) Thus,. 
in the case of chlorine, whose atomic weight is 
35.5, its gramme-atom is 35.5 ; consequently 
35.5 small calories of heat would be required to 
raise one gramme-atom of chlorine through 1 
degree C. 

Atom of Electricity. — (See Electricity, 
Atom of.) 

Atom, Yortex A number of particles 

of the universal ether moving in the manner 
of a vortex ring. 

The theory of vortex atoms, so formed from 
vortex rings, was propounded by Sir William 
Thomson in order to explain how a readily mov- 
able substance, like the universal ether, could be 
made to possess the properties of a rigid solid. If 
it be granted that a vortex motion has once been 
imparted to the universal ether, Thomson shows 
that such rings would be indestructible. (See 
Matter, Thomson's Hypothesis of.) 

Atomic Attraction. — (See Attractio7i, 
Ato?nic) 



Ate] 



34 



[Att. 



Atomic Capacity. — (See Capacity, Atom- 



ic) 

Atomic Currents. — (See Currents, Atom- 
ic.) 

Atomic Energy. — (See Energy, Atomic) 
Atomic Heat— (See Heat, Atomic) 

Atomic or Molecular Induced Currents. 

— (See Currents, Induced, Molecular or 
Atomic) 

Atomic Weight. — (See Weight, Atomic) 

Atomicity. — The combining capacity of 
the atoms. 

The relative equivalence of the atoms or 
their atomic capacity. 

The elementary atoms do not always combine 
atom for atom. Some single atoms of certain 
elements will combine with two, three, four, or 
even more atoms of another element. 

The value of the atomic capacity of an atom is 
also called its quantivalence or valency. 
Elements whose atomic capacity is — 

One, are called Monads, or Univalent. 
Two, " Dyads, " Bivalent. 

Three, " Triads, " Trivalent. 

Four, " Tetrads, "Quadrivalent. 

Five, " Pentads, " Quinquivalent 

Six, " Hexads, " Sexivalent. 

Seven, " Heptads, " Septivalent. 

Atomization. — The act of obtaining liquids 
In a spray of finely divided particles. 

In most cases the term is not literally correct, 
as each of the smallest particles so obtained usu- 
ally consist of many thousands of atoms. 

Atomize. — To separate into a fine spray by 
means of an atomizer. (See Atomizer) 

Atomizer. — An apparatus for readily ob- 
taining a finely divided jet or spray of liquid. 

A jet of steam, or a blast of air, is driven across 
the open end of a tube that dips below the surface 
of the liquid to be atomized. The partial vacuum 
so formed draws up the liquid, which is then 
blown by the current into a fine spray. 

Attract. — To draw together. 
Attracted-Disc Electrometer. — (See Elec- 
trometer, Attracted-Disc) 

Attracting 1 . — Drawing together. 



Attraction. — Literally the act of drawing 
together. 

In science the name attraction is given to a 
series of unknown causes which effect, or are as- 
sumed to effect, the drawing together of atoms, 
molecules or masses. 

Attraction and repulsion underlie nearly all 
natural phenomena. While their effects are well 
known, it is doubtful if anything is definitely 
known of their true causes. 

Since attraction, pure and simple, necessitates 
the belief in action at a distance, an action which 
is now generally discredited, we must, strictly 
speaking, regard the term attraction as being but 
a convenient substitution cf the effect for the 
cause. 

It would appear much more reasonable to re- 
gard the effects of attraction as produced by a 
true push exerted from the outside of the bodies. 
According to this notion, two masses of matter 
undergoing attraction are pushed together rather 
than drawn or attracted together. 

It has been suggested that gravitation may per- 
haps be an effect of a longitudinal motion or vibra- 
tory thrust in the universal ether. If this is the 
case, and the ether is sensibly incompressible, the 
velocity of gravitation, it would appear, should be 
almost infinite. 

Attraction, Atomic The attraction 

which causes the atoms to combine. (See 
Affinity, Chemical) 

In the opinion of Lodge, atomic attraction is 
the result of the attraction of dissimilar charges of 
electricity possessed by all atoms, which are capa- 
ble of uniting or entering into chemical combi- 
nation. (See Electricity, Atom of) 

Attraction, Capillary The molec- 
ular attractions that are concerned in 
capillary phenomena. (See Capillarity) 

Attraction, Electro-Dynamic The 

mutual attraction of electric currents, or of 
conductors through which electric currents 
are passing. (See Dynamics, Electro) 

Attraction, Electro-Magnetic The 

mutual attraction of the unlike poles of 
electro-magnets. (See Magnet, Electro) 

Attraction, Electrostatic — The 

mutual attraction exerted between unlike 
electric charges, or bodies possessing unlike 
electric charges. 



Att] 



35 



[Aim 



For example, the pith ball supported on an in- (2.) Magnet poles of unlike names attract each 

sulated string is attracted, as shown at A, Fig. 28, other; thus a north pole 

attracts a south pole, or 
a south pole attracts a 
north pole. 

A small bar magnet, 
N S, Fig. 31, laid on the 

top of a light vessel floating on the surface of a 
liquid, may be readily employed to illustrate the 
laws of magnetic attraction and repulsion. 






31. Floating 
Magnet. 



Attraction, Mass 



-The mutual at- 



Fig. 28. E'ectrostatic 
Attraction. 



Fig. 2Q. Electrostatic 
Repulsion. 



by a bit of sulphur which has been briskly rubbed 
by a piece of silk. As soon, however, as the ball 
touches the sulphur and receives a charge, it is 
repelled, as shown at B, Fig. 29. 

These attractions ai d repulsions are due to the 
effects of electrostatic induction. {See Induction, 
Electrostatic. ) 



The mutual 

unlike magnet 



Attraction, Magnetic — 

attraction exerted between 
poles. 

Magnetic attractions and repulsions are best 
shown by means of the magnetic needle N S, 
.Fig. 30. The N. pole of an approached magnet 



S N 




Fig. 30. Magnetic Attraction. 

attracts the S. pole of the needle but repels the 
JST. pole. 

The laws of magnetic attraction and repulsion 
may be stated as follows, viz.: 

(1.) Magnet poles of the same name repel each 
other; thus, a north pole repels another north 
pole, a south pole repels another south pole! 



traction exerted between masses of matter. 
(See Gravitation) 

Attraction, Molar A term some- 
times employed for mass attraction. 

Gravitation is an example of mass attraction, 
where the mass of the earth attracts the mass of 
some body placed near it. (See Gravitation.) 

Attraction, Molecular The mutual 

attraction exerted between neighboring 
molecules. 

The attraction of like molecules, or those of the 
same kind of matter, is called Cohesion ; that of 
unlike molecules, Adhesion. 

The tensile strength of iron or steel is due to 
the cohesion of its molecules. Paint adheres to 
wood, or ink to paper, by cohesion or the attrac- 
tion between the unlike molecules. 

Attraction of Gravitation. — A term gen- 
erally applied to the mutual attraction be- 
tween masses. (See Gravitation) 

Attractions and Repulsions of Currents. 

— (See Currents, Attractions and Repulsions 
of.) 

Audiphone, — A thin plate of hard rubber 
held in contact with the teeth, and maintained 
at a certain tension by strings attached to one 
of its edges, for the purpose of aiding the 
hearing. 

The plate is so held that the sound-waves from 
a speaker's voice impinge directly against its flat 
surface. It operates by means of some of the 
waves being transmitted to the ear directly 
through the bones of the head. 

The audiphone is sometimes called a denti- 
phons. 

Aural Electrode. — (See Electrode, Aural) 

Aurora Australis. — The Southern Light. 

A name given to an appearance in the south- 



Aur.] 



36 



[Aut* 



ern heavens similar to that of the Aurora 
Borealis. (See Aurora Borealis.) 

Aurora Borealis. — The Northern Light. 

Luminous sheets, columns, arches, or pillars 
of pale, flashing light, generally of a red color, 
seen in the northern heavens. 

The auroral light assumes a great variety of ap- 
pearances, to which the terms auroral arch, bands, 
cor once, curtains and streamers are applied. 

The exact cause of the aurora is not as y^t 
known. It would appear, however, bt-yond any 
reasonable doubt, that the auroral flashes are due 
to the passage of electrical discharges through the 
upper, and therefore rarer, regions of the atmos- 
phere. The intermittent flashes of light are prob- 
ably due to the discharges being influenced by the 
earth's magnetism. 

Auroras are frequently accompanied by mag- 
netic storms. (See Storm, Magnetic. ) 

The occurrence of auroras is nearly always 
simultaneous with that of an unusual number of 
sun spots. Auroras are therefore probably con- 
nected with outbursts of the solar energy. (See 
Spots, Sun. ) 

The auroral light examined by the spectroscope 
gives a spectrum characteristic of luminous gaseous 
matter, i. e , contains a few bright lines; but, ac- 
cording to S. P. Thompson, this spectrum is pro- 
duced by matter that is not referable with cer- 
tainty to that of any known substance. 

Whatever may be the exact causs of auroras, 
their appearance is almost exactly reproduced by 
the passage of electric discharges through vacua. 

Aurora Polaris. — A general term some- 
times applied to aurora in the neighborhood 
of either pole, or in either the northern or 
the southern hemisphere. 

Auroral Arch. — (See Arch, Auroral.) 
Auroral Bands. — [See Bands, Auroral?) 
Auroral Coronae. — (See Coronce, Au- 
roral.) 

Auroral Curtain. — (See Curtain, Au- 
roral.) 

Auroral Flashes. — (See Flashes, Auroral.) 
Auroral Light. — (See Light, Auroral) 
Auroral Storm.— (See Storm, Auroral) 
Auroral Streamer. — v See Streamer, Au- 
roral) 
Auroras and Magnetic Storms, Peri- 



odicity of Observed coincidences be- 
tween the occurrence of auroras, magnetic, 
storms, and sun-spots. 

The occurrence of auroras, or magnetic storms,, 
at periods of about eleven years apart, corre- 
sponds to the well-known eleven-year sun-spot 
period. 

The period also agrees with a variation in the- 
magnetic declination of any place, which, accord- 
ing to Sabine, occurs once in every eleven years.. 

Austral Magnetic Pole. — (See Pole, Mag- 
netic, Austral) 

Autographic Telegraphy. — (See Teleg- 
raphy, Autographic.) 

Automatic Annunciator Drop. — (See 
Drop, Annunciator, Automatic.) 

Automatic Bell. — v See Bell, Automatic 
Electric.) 

Automatic Contact Breaker. — (See Con- 
tact Breaker, Automatic) 

Automatic Cut-Out. — [See Cut-Out, Au- 
tomatic) 

Automatic Cut-Out for Multiple-Connect- 
ed Electro-Receptive Devices. — (See Cut- 
Out, Automatic, for Multiple-Connected- 
Electro-Receptive Devices.) 

Automatic Cut-Out for Series-Connected 
Electro-Receptive Devices. — (See Cut-Out r 
Auto7natic,for Series-Connected Electro-Re- 
ceptive Devices) 

Automatic Drop. — (See Drop, Auto- 
matic) 

Automatic Electric Burner. — [See Burn- 
er, Autoinatic Electric.) 

Automatic Electric Safety System for 
Railroads. — (See Railroads, Auto?natic Elec- 
tric Safety System for.) 

Automatic Fire-Alarm. — (See Alarm,., 
Fire, Automatic) 

Automatic Gas Cut-Off. — (See Cut-Off, 
Automatic Gas.) 

Automatic Indicator. — (See Indicator, 
Automatic ) 

Automatic Make-and-Break. — (See Make- 
and-Break, Automatic) 

Automatic Oiler. — (See Oiler, Autojnatic)} 



Aut, 



37 



B. A. U. 



Automatic Paper-Winder. — (See Winder, 
Telegraphic Paper.) 

Automatic Regulation. — ( See Regulation, 
Automatic?) 

Automatic Regulator. — (See Regulator, 
Automatic?) 

Automatic Search-Light. — (See Light, 
Search, Automatic?) 

Automatic Switch for Incandescent Elec- 
tric Lamp. — (See Switch, Autoinatic, for 
Incandescent Electric Lamp.) 

Automatic Telegraphy. — (See Teleg- 
raphy, Automatic.) 

Automatic Telephone Switch. — (See 
Switch, Telephone, Automatic?) 

Automatic Time Cut-Outs.— (See Cut- 
Out, Automatic Time.) 

Automatic Variable Resistance. — (See 
Resistance, Variable, Automatic?) 

Automatically Regulable. — (See Regula- 
ble, Automatically?) 

Automobile Torpedo. — (See Torpedo, Au- 
tomobile?) 

Average or Mean Electromotive Force. — 
(See Force, Electroinotive, Average, or 
Mean?) 

Axes of Co-ordinates. — (See Co-ordinates, 
Axes of.) 

Axial Magnet. — (See Magnet, Axial?) 

Axis, Magnetic The line around 

which a magnetic needle, free to move, but 
which has come to rest in a magnetic field, 
can be turned without changing the set or 
direction in which it has come to rest. 

Axis, Magnetic, of a Straight Needle 

— A straight line drawn through the magnet, 
joining its poles. 



The magnetic axis of a straight needle may be 
regarded as a straight line passing through the 
poles of the needle and its point of support. 

The magnetic axis may not correspond with 



the geometric axis of the 
needle. This leads to 
an error in reading the 
true direct on in which 
the needle is pointing, 
which must be cor- 
rected. Thus, the nee- 
dle N S, Fig. 32, points 
to 31 degrees on the 
scale. In reality, if the 
magnetic axis of the 
needle lies in the line 
N' S', the true deflec- 
tion of the needle is only 
28 degrees. 



25 30 35 4Q 




Fig- 32. Magnetic 
Axis. 



Axis of Abscissas. — (See Abscissas, Axis 
of) 

Axis of Ordinates. — (See Ordinates, Axis 
of.) 

Azimuth. — In astronomy, the angular dis- 
tance between an azimuth circle and the 
meridian. 

The azimuth of a heavenly body in the North- 
ern Hemisphere is measured on the arc of the 
horizon intercepted between the north point of 
the horizon and the point where the great circle 
that passes through the heavenly body cuts the 
horizon. 

Azimuth Circle.— (See Circle, Azimuth?) 

Azimuth Compass. — (See Compass, Azi- 
muth?) 

Azimuth, Magnetic The arc inter- 
cepted on the horizon between the magnetic 
meridian and a great circle passing through 
the observed body. 



B. — A contraction used in mathematical 
writings for the internal magnetization, or the 
magnetic induction, or the number of lines of 
force per square centimetre in the magnetized 
material. 

This contraction for internal magnetization is, 



in most mathematical treatises, printed in bold- 
faced type. 

B. A. Ohm.— (See Ohm, B. A.) 

B. A. U. — A contraction sometimes em- 
ployed for the British Association unit or ohm. 



B. W. G.] 



38 



[Bal. 



B. W. 0.— A contraction for Birmingham 
wire gauge. (See Gauge, Birmingham 
Wire.) 

A contraction sometimes used for the new- 
British wire gauge. 

Back Electromotive Force.— (See Force, 
Klectrejnotive, Back?} 

Back-Stroke of Lightning. — (See Light- 
ning, Back-Stroke of.) 

Bain's Chemical Recorder.— (See Re- 
corder, Chemical, Bain's?) 

Bain's Printing Solution. — (See Solution, 
Bains Printing?) 

Balance Arms. — (See Ar?ns, Bridge or 
Balance?) 

Balance, Bi-filar Suspension An 

instrument similar in construction to Cou- 
lomb's torsion balance, but in which the 
needle is hung by two separate fibres instead 
of by a single one. (See Balance, Coulomb's 
Torsion. Suspension, Bi-filar?) 



A standard Thomson centi-ampere balance 
is shown in Fig. 33. In measuring a current, 



-An am- 



Balance, Centi-Ampere — 

meter in the form of a balance, whose scale is 
graduated to give direct readings in centi- 
amperes. 

Ampere balances giving readings in various 
decimals or multiples of amperes have been de- 
vised by Sir William Thomson. The strength of 
current passing is determined by the action on a 
movable ring or coil, placed between two fixed 
rings or coils. 

The movable ring is in a horizontal plane 
nearly midway between the two fixed rings. 
The fixed rings are traversed by the current 
in opposite directions, so that one attracts 
and the other repels the movable ring. The 
movable ring is attached to one end of a horizon- 
tal balance arm, and a similar movable ring, also 
provided with attracting and repelling fixed rings, 
is attached to the opposite end of the balance arm. 
In order to avoid disturbance of horizontal com- 
ponents of terrestrial, or of local magnetic force, 
the current is sent in the same direction through 
the two movable rings. The balancing is effected 
by means of a weight, sliding on a nearly hori- 
-zontal arm attached to the balance. A counter- 
poise weight is used in connection with the sliding 
weight. 




Centv 



re, Balance. 



Fig. 33- 

the weight is moved along the scale untd the 
balance comes to rest. 

Balance, Composite — A balance 

form of ammeter devised by Sir William Thom- 
son, which can be used for an ampere-meter, a 
watt-meter, or a volt-meter, according to the 
manner in which its sets of fine and coarse 
wire coils are connected. (See Balance, 
Cent i- A ?nfiere?) 

Balance, Coulomb's Torsion An 

apparatus to measure the force of electric or 
magnetic repulsion between two similarly 
charged bodies, or between two similar mag- 
net poles, by opposing to such force the tor- 
sion of a thin wire. 

The two forces balance each other ; hence the 
origin of the name. 




Coulomb's Torsion Balance. 



Fig- 34. 

Fig. 34 represents a Coulomb torsion bal- 
ance, adapted to the measurement of the force 



Bal.J 



39 



[BaJ. 



of electrostatic repulsion. A delicate needle of 
shellac, having a small gilded pith ball at one of 
its ends, is suspended by a fine metallic wire. A 
proof-pla,7ie, B, is touched to the electrified surface 
whose charge is to be measured, and is then 
placed as shown in the figure. (See Plane, Proof.) 
There is a momentary attraction of the needle, 
and then a repulsion, which causes the needle to 
be moved a certain distance from the ball on the 
proof-plane. This distance is measured in degrees 
•on a graduated circle a a, marked on the instru- 
ment. The force of the repulsion is calculated by 
determining the amount of torsion required to 
move the needle a certain distance toward the 
ball of the electrified proof-plane. 

This torsion is obtained by the movement of the 
torsion head D, the amount of which motion is 
measured on a graduated circle at D. The 
measurement is based on the fact that the force re- 
quired to twist a wire is proportional to the angle 
-of torsion. 

Balance, Deci-Ampere — 



connected as shown, A and B, in the circuit of a 
battery, and C and D, in the circuit of a telephone. 
The coils, A and B, and C and D, are placed at 



— An ammeter 
in the form of a balance, whose scale is 
graduated to give direct readings in deci- 
amperes. (See Balance, Centi-Ampere) 

Balance, Deka-Ampere — An am- 
meter in the form of a balance, whose scale is 
graduated to give direct readings in deka- 
amperes. (See Balance, Centi-A?npere) 

Balance, Electric A term fre- 
quently used for Wheatstone's electric bridge. 
(See Bridge, Electric.) 

The electric bridge is sometimes called a balance 
because, when in use in measuring resistances, 
one resistance or set of resistances balances an- 
other resistance or set of resistances. 

Balance, Hekto-Ampere An am- 
meter in the form of a balance, whose scale 
is graduated to give direct readings in hekto- 
amperes. (See Balance, Centi-Amftere.) 

Balance Indicator.— (See Indicator, Bal- 
ance.) 

Balance, Induction, Hughes' — 

An apparatus for the detection of the presence 
of a metallic or conducting substance by the 
aid of induced electric currents. 

Hughes' induction balance is shown in Fig. 35. 

A, B, C and D are bobbins, wound with about 
300 feet of No. 32 copper wire. The coils are 




F*g- 35- Hughes' Induction Balance. 

such a distance apart as to prevent any mutual 
induction occurring between them. The coils 
are so joined that the direction of the induction 
of A, on C, is opposite to that of B, on D. 

The coils, A and B, then act as primaries, and C 
and D, as secondaries. In the battery circuit is an 
interrupter I, which is caused to continually make 
and break the circuit. 

The coils are so adjusted that the opposing 
secondary coils produce but little noise to one 
listening at the telephone. This can readily be 
done by the adjusting of a single pair of coils. 

If a single coin or mass of metal be introduced 
between either A and C, or B and D, or even 
above one of the coils, as at d, the balance 
will be disturbed, since some of the induction is 
now expended in producing electric currents in 
the interposed metal, and a sound will therefore 
be heard in the telephone. But if precisely similar 
metals are placed in similar positions, between A 
and C, and B and D, no sound is heard in the 
telephone, since the inductive effects due to the 
two metals are the same. 

The slightest difference, however, either in 
composition, size or position, destroys the balance, 
and causes a sound to be heard in the telephone. 

A spurious coin is thus readily detected when 
compared v/ith a genuine coin. 

A somewhat similar instrument has been em- 
ployed to detect and locate a bullet or other for- 
eign metallic substance in the human body. 

In order to determine the amount of the dis- 
turbance, an instrument called a sonometer is 
used (See Sonometer, Hughes' 1 ), in which a single 
secondary coil, placed in the circuit of a telephone, 
slides on a graduated bar between two fixed 
primary coils, so wound as to exert equal and op- 
posite inductions on the secondary. When, there- 
fore, the secondary is exactly in the middle of the 



Bal.] 

graduated bar, and consequently exactly midway 
between the two fixed primary coils, no sounds are 
heard in the telephone, but when moved to one 
side or the other the sounds are heard. Switches 
are so arranged that the telephone can be readily 
switched from the induction balance to the tele- 
phone, or vice versa. When, therefore, a metallic 
disc is placed in one of the coils of the induction 
balance, and a noise is heard in the telephone, 
the coil of the sonometer is shifted so that the 
noise heard in this telephone is judged by the 
ear to be equal, and the comparison can then be 
made by means of simple calculations. 

The following table gives, in arbitrary values, 
the results of various experiments as to the sensi- 
tiveness in this respect of discs of different 
metals, of various sizes and shapes : 

Silver, chemically pure 125 

Gold 117 

Silver, commercial 115 

Aluminium 112 

Copper 100 

Zinc 80 

Bronze 75 

Tin 74 

Iron, ordinary 53 

German silver 50 

Iron, pure 40 

Copper, alloyed 40 

Lead 58 

Antimony 35 

Bismuth 10 

Zinc, alloyed 6 

Carbon 2 

— {Fleming.) 

An inspection of this table shows that the values 
found for different metals do not correspond with 
their electric conducting power, although, roughly 
speaking, the best conductors stand at the top of 
the table, and the worst at the bottom. The 
effects appear to be dependent for their action on 
the phenomena of magnetic screening, for — 

(1.) If slots are cut in the middle of the plate 
its disturbing action is either removed or very 
much decreased. 

(2.) If a flat coil of copper wire replaces a disc 
of metal no effect is produced on the induction 
balance when its ends are open, but when closed 
the coil acts just like a disc, or continuous plate 
of metal. 

(3.) The difference between various metals in- 



40 [Bal.. 

serted as discs in the induction balance is less at 
high speeds of reversal than at low speeds. 

Balance, Kilo-Ampere — An am- 
meter in the form of a balance, whose scale is 
graduated to give direct readings in kilo-am- 
peres. (See Balance, Ce?iti- Ampere.) 

Balance of Induction in Cable. — (See 
Induction, Balance of, in Cabled) 

Balance, Plating An automatic 

device for disconnecting the current from 
the article to be plated, as soon as a certain 
increase in weight has been obtained. 

The objects to be plated are suspended at one 
end of a balance, and when a certain increase in 
weight has been gained, the balance tips and 
breaks the circuit. Edison's electric meter is 
based on this principle. * 

Balance, Thermic, or Bolometer. — An 

apparatus constructed on the principle of the 
differential galvanometer, devised by Professor 
Langley for determining small differences of 
temperature. (See Galvanometer, Differen- 
tial.) 

A coil composed of two separately insulated 
wires, wound together, is suspended in a mag- 
netic field, and has a current sent through it. 
Under normal conditions, this current separates 
into two equal parts, and runs through the wires 
in opposite directions. It therefore produces no 
sensible field, and suffers no deflection by the field 
in which it is suspended. 

Any local application of heat producing a dif- 
ference in temperature in these coils, causing a 
difference in resistance, prevents this equality. A 
field is therefore produced in the suspended coil, 
which, though extremely small, is rendered meas- 
urable by means of the powerful field produced 
in the coil, within which the double coil is sus- 
pended. 

Differences of temperature as small as one- 
fourteen thousandth of a degree Fahrenheit are 
detected by the instrument. 

Balance, Wheatstone's Electric A 

name often given to the electric bridge or 
balance. (See Bridge, Electric?) 

Balanced-Metallic Circuit. — (See Circuity 
Balanced-Metallic) 

Balanced Resistances. — (See Resistances, 
Balanced.) 



Bal, 



41 



[Bar. 



Balata.— An insulating material. 
Balata, when prepared for use as an insulating 
material, is somewhat like gutta-percha. 

Ball, Electric Time A ball, sup- 
ported in a prominent position on a tall pole, 
and caused to fall at the exact hour of noon, 
or at any other predetermined time, for the 
purpose of thus giving correct time to an 
entire neighborhood. 

The release of the ball is effected by the closing 
of an electric circuit, either automatically, or 
through the agency of an observer. 

Ball, Fire A term sometimes ap- 
plied to globular lightning. (See Lightning, 
Globular) 

Ball Lightning. — (See Lightning, Ball) 

Ballistic Curve. — (See Curve, Ballistic) 

Ballistic Galvanometer. — (See Galva- 
nometer, Ballistic.) 

Balloon, Electric A balloon, or 

air ship, provided with electric power so as 
to be able to be steered or moved against the 
direction of the wind. 

Electric balloons have been moved against the 
wind and steered with a certain amount of success, 
by the use of electric motors driven by storage 
batteries. All that is needed to make aerial navi- 
gation a commercial success is the ability to ob- 
tain great power with a small weight. The storage 
battery does this to a limited extent. 

Bearing in mind the high efficiency of the elec- 
tric motor, it would appear that the problem of 
successful aerial navigation will be solved when 
the discovery is made of means for directly con- 
verting the chemical potential energy of coal into 
electrical energy. 

Balloon Signaling for Military Pur- 
poses. — (See Signaling, Balloon, for Mil- 
itary Purposes) 

Balls, Pith Two balls of pith, sus- 
pended by conducting threads of cotton to 
insulated conductors, employed to show the 
electrification of the same by their mutual 
repulsion. 

The pith balls connected with the insulated 
cylinder A B, Fig. 36, not only show the electii- 
fication of the cylinder, but serve also to roughly 



indicate the peculiarities of distribution of the 
charge thereon. 




Fig. 36. Pith Ball Cylinder. 



Bands, 



Auroral 



-Approximately 



parallel streaks of light sometimes seen 
during the prevalence of the aurora. (See 
Aurora Borealis.) 

Bank of Lamps.— (See Lamps, Bank of) 

Banked Battery. — (See Battery, Banked) 

Bar, Detorsion A bar placed in a 

magnetic instrument called a declinometer for 
the purpose of removing the torsion of the 
suspending thread of the magnet. 

The detorsion ^ar of the declinometer is gen- 
erally made of gun metal of the same weight as 
that of the suspended magnet. A small magnet 
is placed in a rectangular aperture in the middle 
of the bar. 

Bar Electro-Magnet.— (See Magnet, 
Electro, Bar) 

Barad. — A unit of pressure proposed by 
the British Association. 

One barad equals one dyne per square centi- 
metre. 

Barometer. — An apparatus for measuring 
the pressure or weight of the atmosphere. 

Barometric Column. — (See Colu?nn, Baro- 
metric) 

Bars, Bus Omnibus bars. (See 

Bars, Omnibus) 

Bars, Krizik's Cores of various 

shapes, provided for solenoids, in which the 
distribution of the metal in the bar is so pro- 
portioned as to insure as nearly as possible a 
uniform attraction or pull while in different 
positions in the solenoid. 



Bar.] 

Krizik's bars of various shapes are shown in 
Fig. 37. It will be observed that in all cases the 



42 




Fig' 37 • Krizik's Bars. 
mass of metal is greater toward the middle of 
the core than near the ends. 

When a core of uniform diameter is drawn into 
a solenoid, the attraction or pull is not uniform in 
strength for different positions of the bar. When 
the bar is just entering the solenoid, the pull is 
strongest ; as soon as the end passes the middle of 
the core the attraction decreases until, when the 
centres of the bar and core coincide, the motion 
ceases, since both ends of the solenoid attract 
equally in opposite directions. By proportioning 
the bars, as shown in the figure, a fairly uniform 
pull for a considerable length may be obtained. 

Bars, Negative-Omnibus — The 

bus-bars that are connected with the negative 
terminal of the dynamos. (See Bars, Omni- 
bus!) 

Bars, Neutral-Omnibus The bus- 
bars that are connected with the neutral 
dynamo terminal in a three-wire system of 
distribution. 



Bars, Omnibus 



-Heavy bars of con- 



ducting material connected directly to the 
poles of dynamo-electric machines, in electric 
incandescent light or electric railway installa- 
tions, and therefore receiving the entire current 
produced by the machine. 

Main conductors common to two or more 
dynamos in an electrical generating plant. 

The terms bus and omnibus bars refer to the 
fact that the entire or whole current is carried by 
them. 

— The bus- 



Bars, Positive-Omnibus — 

bars that are connected with the positive 
terminal of the dynamos. 

Bath, Bi-polar An electro-thera- 
peutic bath, the current applied to which 
enters at one part of the tub, and leaves at 
another part. 



[Bat.. 

The electrodes for the bi-polar bath consist of 
suitably shaped copper plates, generally called 
shovel electrodes. 

Bath, Copper An electrolytic bath 

containing a readily electrolyzable solution 
of a copper salt, and a copper plate acting as 
the anode, and placed in the liquid near the 
object to be electro-plated, which forms the 
kathode. (See Plating, Electro!) 

The sulphate, the cyanMe and the acetate of cop- 
per are used for copper baihs. The use of the sul- 
phate is objectionable. The cyanide is expensive. 
The acetate is therefore very generally employed. 
Wahl gives the following formula for a copper 
bath, viz. : 

Water 1,000 parts. 

Acetate of copper, crystal- 
lized * 20 " 

Carbonate of soda 20 " 

Bisulphite of soda 20 " 

Cyanide of potassium (pure) 20 " 

Bath, Electro-Plating Tanks con- 
taining metallic solutions in which articles. 
are placed so as to be electro-plated. (See 
Plating, Electro!) 

Strictly speaking a plating bath includes not 
only the vessel and its metallic solution, but also 
the metallic plate acting as the anode and the 
article to be plated forming the kathode. 

Bath, Electro-Therapeutic A bath 

furnished with suitable electrodes and used 
in the application of electricity to curative 
purposes. 

Such baths should be used only under the advice 
of a regular physician. 

Bath, Gold An electrolytic bath 

containing a readily electrolyzable solution of 
a gold salt and a gold plate acting as the 
anode, and placed in the liquid opposite the 
object to be plated, which forms the kathode. 
(See Plating, Electro!) 

Electro gilding may be accomp ished either with 
or without the aid of heat. Hot gilding appears 
to give a smoother and cleaner deposit. 

The following is a fairly good solution for a 
gold bath: 

Water i,coo parts. 

Cyanide of potassium, pure. . 20 " 

Gold 10 « 

— (Wahl.) 



Bat,] 



43 



[Bat. 



The gold is first converted into neutral chloride 
by dissolving it in 25 parts of pure hydrochloric 
acid to which 12.5 parts of pure nitric acid has 
been added. When the gold is completely dis- 
solved, the liquid is heated until of a dark red 
color, in order to expel any excess of acid. 

Bath, Head, Electric A variety 

of electric breeze, applied therapeutically to 
the head of the patient. 

The patient is placed on an insulating stool and 
connected with one pole of an electrostatic induc- 
tion machine, the other pole of which is con- 
nected to a circle of insulated points suspended 
over the head. 

Bath, Hydro-Electric A bath in 

which electro-therapeutic treatment is given 
by applying one electrode to the metallic lining 
of the tub, and the other electrode to the body 
of the bather. 

Bath, Multipolar-Electric — An 

electro-therapeutic bath, in which more than 
two electrodes are employed. 

It is not clear that the multipolar-electric bath 
possesses any decided advantages over the bi-polar 
bath. 

Bath, Nickel An electrolytic bath 

containing a readily electrolyzable salt of 
nickel, a plate of nickel acting as the anode 
of a battery and placed in the liquid near the 
object to be coated, which forms the kathode. 
(See Plating, Electro) 

The double sulphate of nickel and ammonium 
(from 5 to 8 parts dissolved in 100 parts of water) 
is used for the bath. Some prefer to add 
sulphate of ammonium and citric acid to the above 
solution. 

Bath, Shower, Electric A shower 

bath in which the falling drops carry electric 
charges to the patient subjected thereto. 

The water is rendered slightly alkaline. One 
pole is immersed in the alkaline water and the 
other connected to a metallic stool on which the 
patient is placed. 

Bath, Silver An electrolytic bath 

containing a readily electrolyzable salt of 
silver and a plate of silver acting as the 
anode of an electric source and placed in the 
liquid near the object to be coated, which 
forms the kathode. v See ~°lating, Electro) 



The double cyanide of silver and potassium 
is the salt usually employed in the silver bath. 

The following bath is recommended by Rose- 
leur: 

Water 1,000 parts. 

Cyanide of potassium (pure) 50 " 
Pure silver 25 " 

The silver (granulated) is treated with pure nitric 
acid (43 degrees Beaume) and converted into 
nitrate of silver. The solution is then heated to 
dryness and subsequently fused. The fused nitrate 
so obtained is dissolved in fifteen times its weight 
of distilled water and treated with a solution of 
cyanide of potassium (10 per cent, of the cyanide), 
by means of which silver cyanide is thrown down 
as a precipitate. This precipitate is then sepa- 
rated and washed. It is added to the 1,000 parts 
of water, dissolved, and the cyanide of potassium 
afterward added, thus forming the double cyan- 
ide required for the bath. 

Bath, Stripping" A bath for remov- 
ing an electro-plating of gold, silver, or other 
metal, either by simple dipping or by electric 
action. 

Bath, Ungilding- A stripping bath 

suitable for the removal of a coating of gold. 
(See Bath, Stripping?) 

Bath, Unipolar-Electric An electro- 
therapeutic bath, the water of which forms 
one of the electrodes of the source, and the 
other electrode is attached to a metallic rod 
fixed at a convenient height above the tub. 

The bath tub is formed of non-conducting sub- 
stances. The terminals of the electrode con- 
nected with the water terminate in metal plates 
located at suitable points in the tub. The cur- 
rent is applied by the patient making and break- 
ing contact at the vertical metal rod with his 
hands. 

The unipolar-electric bath is employed instead 
of local galvanization where it is desired to limit 
the application to especial organs or particular 
parts of the body. In general galvanization the 
patient is placed on an electrode of large sur- 
face, formed of a large sponge covered metallic 
plate, on which he sits or rests. This electrode is 
connected with the kathode of the battery. The 
anode is-connected with a large sponge electrode, 
which is moved regularly over the body of the 
patient; sometimes the moistened hand of the 
operator is used in place of the sponge electrode. 



Bat, 



44 



[Bat. 



Bath, Unsilvering 



-A stripping bath 



suitable for the removal of a coating of silver. 
(See Bath, Stripping?) 

Bathometer. — An instrument invented by 
Siemens for obtaining deep-sea soundings 
without the use of a sounding line. 

The bathometer depends for its operation on 
the varied attraction of the earth for a suspended 
weight in parts of the ocean differing in depth. 
As the vessel passes over deep portions of the 
ocean, the solid land of the bottom, being further 
from the ship, exerts a smaller attraction than it 
would in shallow parts, where it is nearer; for, 
although in the deep parts of the ocean the water 
lies between the ship and the bottom, the smaller 
density of the water as compared with the land 
causes it to exert a smaller attraction than in the 
shallower parts, where the bottom is nearer the 
ship. The varying attraction of the earth is 
caused to act on a mercury column, the reading 
of which is effected by means of an electric con- 
tact. 

Battery, Banked — — — A term some- 
times applied to a battery from which a num- 
ber of separate circuits are supplied with cur- 
rents. 

The term banked -battery is sometimes ap- 
plied to a multiple-arc connected battery. 

Battery, Cautery A term some- 
times employed in electro-therapeutics, for a 
multiple connected voltaic battery adapted for 
producing electric incandescence for cautery 
effects. 

Battery, Closed-Circuit A voltaic 

battery which may be kept constantly on 
closed-circuit without serious polarization. 

The gravity battery is a closed circuit battery. 
As employed for use on most telegraph lines, it is 
maintained on a closed circuit. When an operator 
wishes to use the line he opens his switch, thus 
breaking the circuit and calling his correspondent. 
Such batteries should not polarize. (See Cell, 
Voltaic, Polarization of. ) 

Battery, Connection of, for Quantity 

— A term, now generally in disuse, formerly 
employed to indicate the grouping of voltaic 
cells, now known as parallel or multiple. 

The arrangement or coupling of a number of 
voltaic cells in multiple reduces the internal resist- 



ance of the battery, and thus permits a greater 
current, or quantity, of electricity to pass ; hence 
the origin of the term. 

Battery, Dynamo The combina- 
tion or coupling together of several separate 
dynamo-electric machines so as to act as a 
single electric source. 

The dynamos may be connected to the leads 
either in series, in multiple, in multiple-series or 
in series-multiple. 

Battery, Dynamo, Electric Machine 

— A dynamo battery. (See Battery, Dy- 
namo?) 

Battery, Electric A general term 

applied to the combination, as a single source, 
of a number of separate ejectric sources. 

The separate sources may be coupled either in 
series, in ?nultiple, in multiple-series, or in series- 
multiple. ( See Circuits, Varieties of.) 

The term battery is sometimes incorrectly ap- 
plied to a single voltaic couple or cell. 

Battery, Floating-, De la Rive's A 

floating voltaic cell, the terminals of which are 
connected with a coil of insulated wire, em- 
ployed to show the attractions and repul- 
sions between magnets and movable electric 
circuits. 

The cell, shown in Fig. 38, consists of a vol- 




Fig. 38. Floating Cell. 

taic couple of zinc and copper, the terminals of 
which are connected to the circular coil of insu- 
lated wire, as shown, and the whole floated by 
means of a cork, in a vessel containing dilute sul- 
phuric acid. 

When the current flows through the coil in the 
direction shown by the arrows, the approach of 
the N-seeking pole of a magnet will cause the 
cell to be attracted or to move towards the mag- 
net pole, since the south face or end of the coil is 
nearer the north pole of the magnet. If the other 



Bat.] 



45 



[Bat. 



-end were nearer, repulsion would occur, the cell 
turning round until the south face is nearer the 
magnet, when attraction occurs. 

This is, strictly speaking, a floating cell, and 
not a battery. (See Battery, Voltaic.) 

Battery, Galvanic Two or more 

separate voltaic cells so arranged as to form 
a single source. 

This is more correctly called a Voltaic Battery. 
(See Battery ', Voltaic.) 

Battery, Gas A battery in which 

the voltaic elements are gases as distinguished 
from solids. 

The electrodes of a gas battery generally con- 
sist of plates of platinum, or other solid substance 
which possesses the power of occluding oxygen 
and hydrogen. The lower parts of these plates 
dip into dilute sulphuric acid, and the upper parts 
are respectively surrounded by oxygen and hydro- 
gen gas derived from the electrolytic decompo- 
sition of the dilute acid. 

A gas battery consisting of plates of platinum 
dipping below into acid liquid, and surrounded 
in the space above the liquid by hydrogen and 
oxygen H, H' and O, O', etc., respectively is 
.shown in Fig. 39. 



Battery, Leyden Jar- 




Fig. 3Q. Gas Battery. 

In charging this battery an electric current is 
sent through it until a certain quantity of the 
gases has been produced. If, then, the charging 
current be discontinued, a current in the oppo- 
site direction is produced by the battery. The 
gas battery is in reality a variety of storage bat- 
tery. (See Electricity, Storage of. Cell, Secon- 
dary. Cell, Storage.) 

Gas batteries can also be made by feeding con- 
tinually into the cell a gas capable of acting on 
ihe positive elements. 

Battery Gauge.— (See Gauge, Battery^ 



— The combina- 
tion of a number of separate Leyden jars so 
as to act as one single jar. 

A Leyden jar battery is shown in Fig* 40, 




Fig. 40, Leyden Jar Battery. 

where nine separate Leyden jars are connected 
as a single jar by joining their outer coatings by 
placing them in the box P, the bottom of which 
is lined with tin foil. The inner coatings are 
connected together by the metal rods B, as 
shown. 

A discharging rod A, may be employed for 
connecting the opposite coatings. The handles 
are made of glass or any other good insulating 
material. 

A number of Leyden jars can be coupled in 
series by connecting the inner coating of the first 
jar to the outer coating of the second, the inner 
coating of the second to the outer coating of the 
third, and so on. The battery so obtained is 
then discharged by connecting the outer coat- 
ing of the first jar with the inner coating of the 
last. 



Battery, Local 



-A voltaic battery 



used at a station on a telegraph line to 
operate the Morse sounder, or the register- 
ing or recording apparatus, at that point 
only. (See Telegraphy, American or Morse 
System of.) 

The local battery is thrown into or out of action 
by the telegraphic relay. (See Relay. ) 

Battery, Magnetic The combina- 
tion, as a single magnet, of a number of sep- 
arate magnets. 

A magnetic battery, or compound magnet, is 



Bat] 



46 



[Bat. 



shown in Fig. 41. It consists of straight bars of 
steel, p. p, p, with their similar poles placed near 
together and inserted in 
masses of soft iron, N and 
S, as shown. 

Battery, Main 



The plunge battery shown in Fig. 42, consists; 




The battery, in a system 
of telegraphic communi- 
cation, that is employed 
for sending the signals 
over the main line, as dis- 
tinguished from any bat- 
tery employed for any 
other particular work, 
such, for example, as that 
of the local battery. (See 
Battery. Local.) . "" £^ry. 

Battery, Multiple-Con- found Magnet. 

nected ■ — A battery the single cells of 

which are connected to one another and to the 
mains or conductors in multiple. (See Cir- 
cuit, Multiple?) 

Battery, Open-Circuit A voltaic 

battery which is normally on open-circuit, 
and which is used continuously only for com- 
paratively small durations of time on closed- 
circuit. 

Leclanche-cells form an excellent open-circuited 
battery. They have a comparatively high electro- 
motive force, but rapidly polarize. They cannot 
therefore be economically used for furnishing 
currents continuously for long durations of time. 
When left on open-circuit, however, they readily 
depolarize. They therefore form an excellent 
battery for such work as annunciator bells, burg- 
lar alarms, etc., where the current is only 
required for short periods of time, separated by 
comparatively long intervals of rest. (See Cell, 
Voltaic, Leclanche.) 

Battery Plates of Secondary or Storage 

Cell, Forming of (See Plates of 

Secondary or Storage Cell, Forming of.) 

Battery, Plunge — A number of 

separate voltaic cells connected so as to form 
a single cell or electric source, the plates of 
which are so supported on a horizontal bar 
as to be capable of being simultaneously 
placed in, or removed from, the exciting 
liquid. 




Fig. 42. Plunge Battery* 

of a number of zinc-carbon elements immersed in 
an electrolyte of dilute sulphuric acid, or in elec~ 
tropolon liquid, contained in separate jars, J, J. 
(See Liquid, Electropoion.) 

The mode of support to the horizontal bar- 
will be understood front an inspection of the 
drawing. 

Battery, Primary The combina- 
tion of a number of separate primary cells so- 
as to form a single source. 

The term primary battery is used in order to 
distinguish it from secondary or storage battery, 
(See Cell, Secondary. Cell, Storage.) 

Battery, Secondary The combina- 
tion of a number of separate secondary or 
storage cells, so as to form a single electric 
source. (See Electricity, Storage of.) 

Battery, Selenium The combina- 
tion of a number of separate selenium cells so 
as to form an electric source. (See Cell,. 
Selenium?) 

Battery, Series-Connected A bat- 
tery, the separate cells of which are con- 
nected to one another and to the line or 
conductor in series. (See Circuit, Series?) 

Battery Solution. — (See Solution, Bat- 
tery?) 

Battery, Split A voltaic battery 

connected in series, but having one of its 
middle plates connected with the ground. 

By the employment of the device of a split- 
battery, the poles of the battery are maintained 
at potentials differing in opposite directions from 
the potential of the earth. 

Battery, Storage A number of 

separate storage cells connected so as to* 
form a single electric source. 



Bat.] 



47 



[Bel. 



A cell of a storage battery is shown in Fig. 



43- 




Fig. 43. Storage Battery. 

Battery, Storage, Element of A 

single set of positive and negative plates of a 
storage cell connected so as to be ready for 
placing in the acid liquid of the jar or cell. 

A term sometimes applied to one of the 
storage cells in a storage battery. 

This latter use of the term element is unfortu- 
nate, since from the analogous case of a pnmary 
cell, an element would consist of a single plate, 
either positive or negative, and not of both. That 
is, every voltaic couple consists of two elements, 
the positive and the negative. 

Battery, Thermo A term often 

applied to a thermo-electric battery. (See 
Battery, Tkermo-Electric.) 

Battery, Thermo-Electric The 

combination, as a single thermo-electric cell, 
of a number of separate thermo-electric cells 
or couples. (See Couple, Thermo-Electric?) 

Battery, Toltaic The combina- 
tion, as a single source, of a number of sepa- 
rate voltaic cells. 

Battery, Water A battery formed 

cf zinc and copper couples immersed in an 
electrolyte of ordinary water. 

Any voltaic couple can be used, the positive 
element of which is slightly acted on by water. 
When numerous couples are employed consider- 
able difference of potential can be obtained. 

Water batteries are employed for charging 
electrometers. They are not capable of giving 
any considerable current, owing to their great in- 
ternal resistance. 



Bead Areometer or Hydrometer. — (See 

Areometer, Bead.) 

Bec-Carcel. — The Carcel, or French unit 
of light. (See Carcel?) 

Bell, Automatic-Electric An elec- 
tric bell furnished with an automatic contact- 
breaker. (See Contact-Breaker , Automatic?) 

A form of automatic-electric bell is shown in 
Fig. 44. The relation of the electro-magnet, its 
armature and the bell 
lever, will be readily 
understood from an in- 
spection of the draw- 
ing. 

Bell, Call 




An electric bell used 
to call the attention 
of an operator to the 
fact that his corre- 
spondent wishes to 
communicate with 
him. 

Bell, Circular 

— A bell so construct- 
ed that all its moving 

parts are contained in Figm 44 , Automa tic Electr 'c 
the gong. Bell. 

Bell, Continuous-Sounding 1 Electric 

— An electric bell, which, on the completion 
of the circuit, continues striking until stopped 
either by hand or automatically. 

On the completion of the circuit, the attraction 
of an armature throws a catch off from a lever, 
and thus permits the lever to fall and complete a 
contact and allows the current to ring the bell; or 
the bell is rung by clockwork, which is thrown 
into action by the passage of a current through an 
electro-magnet. (See Bell, Electro-Mechanical .) 

Bell, Differential Electric An 

electric bell, the magnetizing coils of which 
are differentially wound. 

Differential winding is ot advantage where a 
very strong current is required, as this winding 
decreases the sparking at the contacts, on the 
opening of the circuit. 

Bell, Electro-Magnetic, Siemens- Anna* 
ture Form A form of electro-mag- 



Bel.] 



48 



[Bel. 




netic bell in which the movements of the bell 
armature are obtained by the reversal of 
polarity that takes place when alternating cur- 
rents are pass- 
ed through the 
coils of a sim- 
ple, single coil, 
Siemens - arma- 

Fzg. 45, Siemens-Armature Form 
The details of Electro-Magnetic Lell. 

will be readily understood from an examination 
of Fig. 45. 

Bell, Electro-Mechanical A bell, 

the striking apparatus of which is driven by 
a weight or spring, called into action by the 
movement of the armature of an electro- 
magnet. (See Alarm, Electric?) 

Bell, Extension-Call A device for 

prolonging the sound of a magneto call. 

An alarm bell is automatically connected with 




m v 



Fig. 4b. Extension-Call Bed. 
the circuit of a local battery by means of the cur- 
rent generated by the magneto-call, and continues 
sounding after the current of the magneto call 
has ceased. 

A form of extension-call bell is shown in Fig. 46. 

Bell, Indicating" An electric bell 

in which, in order to distinguish between 
different bells in the same office, a number 
is displayed by each bell when it rings. 

Bell, Magneto-Electric An electric 

bell, the current employed to operate or 
strike which is obtained by the motion of a 
magneto-electric machine. 

Bell, Night In a telephone ex- 
change, a bell, switched into connection with 
the shunted circuit of an annunciator case, and 
intended, by its constant ringing, to call the 
attention of the night operator to the falling 
of a drop. 



Bell, Belay, Electric An electric 

bell in which a relay magnet is employed to 
switch a local battery into the circuit of the 
sounding apparatus of the bell. 

The relay bell is suitable for use when the bell 
to be sounded is situated at a great distance. As 
the current from the line, when this is long, is 
too weak to ring the bell, it throws into action a 
local battery by the action of a relay. 

Relay bells were used in the early forms of 
acoustic telegraphs as employed in England with 
telay sounders. 

The dots and dashes of the Morse alphabet were 
indicated by the sounds of two bells, a tap on 
one bell indicating a dot, and a tap on the other 
a dash. This system is now practically aban- 
doned. 



(See Magnet, Bell- 



-An electric 



Bell-Shaped Magnet.— 

Shaped?) 

Bell, Shunt, Electric 

bell, the magnetizing coils of which are placed 
on the line in shunt. 

In the case of shunt-connected electric bells, 
one of the bells must make and break the circuit 
for all the rest. The series-connected electric 
bell is used where the distance between the sepa- 
rate bells is great, in order to save the expense of 
multiple connections. 

In most cases, where a number of electric bells 
are to be simultaneously sounded, connection in 
multiple is adopted. 

Bell, Single-Stroke Electric An 

electric bell that gives a single stroke only for 
each make of the circuit. 




Fig. 47. Single-Stroke Bell. 

Since the bell gives a single stroke for each 
completion of the circuit, its use permits of ready 
communication between any two places by any 



Bel.] 



49 



[Bla. 



system of prearranged signals. A buzzer may be 
used for the same purpose. A form of single- 
stroll bell is shown in Fig. 47. On completing the 
c'rcuit, the current, through its coils, attracts the 
armature and causes a single stroke of the bell. 

Bell, Telephone-Call A call bell 

used to call a correspondent to the telephone. 

The telephone-call bell is generally a magneto- 
electric bell. 

Bell, Trembling' A name some- 
times given to a vibrating or an automatic 
make-and-break bell. (See Make-and-Break, 
Automatic.) 

A trembling" bell. 



■(See Tongue, 
-(See Cell, Vol- 
Suspension, 
-(See Bal- 



Bell, Vibrating- — 

(See Bell, Trembling?) 

Bias of Relay Tongue.- 
Relay, Bias of.) 

Bichromate Toltaic Cell. 
taic, Bichromate?) 

Bi-filar Suspension. — (See 
Bi-filar?) 

Bi-filar Suspension Balance. 
ance, Bi-filar Suspension?) 

Bi-filar Winding.— (See Winding, Bi- 
filar.) 

Binary Compound.-— (See Compound, Bi- 
nary?) 

Binding- Coils. — (See Coils, Binding.) 

Binding-Post.— (See Post, Binding.) 

Binding-Screw. — (See Screw, Binding?) 

Binding- Wire for Telegraph Lines. — (See 
Wire, Bi?iding,for Telegraph Lines?) 

Biology, Electro That branch of 

electric science which treats of the electric 
conditions of living animals and plants, and 
the effects of electricity upon them. 

Electro-Biology includes : 

(1.) Electro-Physiology. 

(2.) Electro-Therapy, or Electro-Therapeutics. 

Bioplasm.— Any form of living matter pos- 
sessing the power of reproduction. 

Bioscopy, Electric The determina- 
tion of the presence of life or death by the 
passage of electricity through the nerves and 
muscles. 

Bi-polar.— Having two poles. 



Bi-polar Armature. — (See Ariiiature, 
Bi-polar?) 

Bi-polar Bath. — (See Bath, Bi-polar?) 

Birmingham Wire Gauge. — (See Gauge, 
Wire, Birm ingh am.) 

Bi-Telephone. — (See Telephone, Bi.) 

Bitite. — A variety of insulating material. 

Black Electro-Metallurgical Deposit. — 
(See Deposit, Black Electro- Metallurgical?) 

Black Lead. — A variety of carbon em- 
ployed in various electrical processes. 

Black lead is also termed plumbago or graphite, 
(See Plumbago. Graphite.) 

The term black lead is a misnomer, since the 
substance is carbon and not lead. The term is an 
old one, and is still very generally used. 

Blasting-, Electric The electric 

ignition of powder or other explosive material 
in a blast. (See Fuse, Electric?) 

The current required for the ignition of the 
fuse is generally obtained by means of a magneto- 
electric machine. In the form of magneto-blast- 
ing machine, shown in Fig. 48, the movement 




Fig. 48. Magneto- Blasting Machine. 

of the handle shown at the top of the figure 
causes the rapid rotation of a cylindrical armature 
constructed on the Wheatstone and Siemens prin- 
ciple. The magnets are of iron, and are furnished 



Ble.] 



50 



[Boa. 



with coils of insulated wire. On the rotation of 
the armature the current developed therein in- 
creases the field of the field magnet, and, when 
of the proper degree of intensity, is thrown into the 
outer circuit, and ignites the fuse. 

Bleaching, Electric Bleaching pro- 
cesses in which the bleaching agents are 
liberated, as required, by the agency of electro- 
lytic decomposition. 

In the process of Naudin and Bidet, the cur- 
rent from a dynamo-electric machine is passed 
through a solution of common salt between two 
closely approached electrodes. The chlorine and 
sodium thus liberated react on each other and 
form sodium hypochloride, which is drawn off 
by means of a pump and used for bleaching. 
(See Electrolysis.) 

Block, Branch ■ —A device em- 
ployed in electric wiring for taking off a branch 
from a main circuit. (See Wiring) 

A form of branch-block, with its fuses attached, 
is shown in Fig. 49. 



charged conductor by a convection dis- 
charge. 

The candle flame, Fig. 50, is blown in the di- 




Fig. 4Q. Branch'Block. 

Block, Cross-Over A device to 

permit the safe crossing of one wire over 
another in molding or cleat wiring. 

Block, Fuse A block containing 

a safety fuse or fuses for incandescent light 
circuits. (See Fuse, Safety) 

Block System for Railroads.— (See Rail- 
roads, Block System for) 

Block Wire.— (See Wire, Block) 

Blow-Pipe, Electric A blow-pipe 

in which the air-blast is obtained by a stream 
of air particles produced at the point of a 




Convection Blozv-Pipe. 

rect ; on of the stream of air particles passing off 
from the point P. (See Convection, Electric.) 

Blow-Pipe, Electric-Arc A de- 
vice of Werdermann for cutting rocks, or 
other refractory substances, in which the heat 
of the voltaic arc is directed, by means of a 
magnet, or a blast of air, against the substance 
to be cut. 

The carbons are placed parallel, so as to readily 
enter the cavity thus cut or fused. This inven- 
tion has never been introduced into extensive 
practice. 

In the welding process of Benardos and 
Olzewski, the welding temperature is obtained by 
means of an electric arc taken between two suit- 
ably shaped electrodes. 

In the electric-arc 
blow - pipe, shown in 
Fig. 51, the voltaic arc, 
taken between two ver- 
tical carbon electrodes, 
is deflected into a hori- 
zontal position under the 
influence of the inclined 
poles of a powerful elec- 
tro-magnet. 

The highly heated car- 
bon vapor which consti- 
tutes the voltaic arc is deflected by the magnet in 
the same direction as would be any other mov- 
able circuit or current. 

Board, Cross-Connecting* In a 

system of telegraphic or telephonic communi- 
cation, a board to which the line terminals are 
run before entering the switchboard, so as to 




r / . Electric- Arc 
Blozv-Pipe. 



Boa.] 



51 



readily place any subscriber in connection 
with any desired section of the switchboard. 

Board, Fuse ' A board of slate or 

other incombustible material on which all 
the safety fuses in an installation are as- 
sembled. 

The fuse board is used for avoiding accidents 
from the firing of the fuses. 

Board, Hanger A form of board 

provided for the ready placing or removal of 
an arc lamp from a circuit. 




Fig. 52. Hanger-Board. 

A hanger-board contains a switch or cut-out for 
the ready opening or closing of the circuit. A 
.form of hanger-board is shown in Fig. 52. 

Board, Key Any board to which 

are connected electric keys or switches. 

Board, Legging-Key A key board 

employed for the purpose of legging an 
operator into a circuit connecting two or more 
subscribers. (See Leg) 

Board, Multiple Switch A board 

to which the numerous circuits employed in 
systems of telegraphy, telephony, annunciator 
or electric light and power circuits are con- 
nected. 

Various devices are employed for closing these 
circuits, or lor connecting or cross-connecting 
them with one another, or with neighboring cir- 
cuits. 

A multiple switchboard, for example, for a tele- 
phone exchange, will enable the operator to con- 
nect any subscriber on the line with any other 
subscriber on that line, or on another neighbor- 



ing line provided with a multiple switchboard. 
To this end the following parts are necessary: 

(I.) Devices whereby each line entering the ex- 
change can readily have inserted in its circuit a 
loop connecting it with another line. This is 
accomplished by placing on the switchboard a 
separate spring-jack connection for each sepa- 
rate line. This connection consists essentially 
of one or two springs made of any conducting 
metal, which are maintained in 
metallic contact when the plug 
key is not inserted, but which are 
readily separated from one another 
by the introduction of the plug- 
key, Fig. 53, the terminals, a and 
b, of which are insulated from 
each other, and are connected to 
the ends of a loop coming from 
another line. As the key is in- 
serted, the metallic spring or 
springs of the spring-jack are separated and the 
metallic pieces, a and b, are brought into good 
sliding contact therewith, thus introducing the 
loop into the circuit. (See Spring- Jack.) 

(2.) As many separate annunciator-drops as 
there are separate subscribers. These are pro' 
vided so as to notify the Central Office of the par- 
ticular subscriber who desires a connection. 
Alarm-bells to call the operator's attention to the 
calling subscriber, or to the falling of a drop, are 
generally added. (See Bell, Call.) 

(3.) Connecting cords and keys for connecting 
the operator's telephone, and means for ringing 
subscribers' bells, and clearing out drops. 




ifadl 



F&-53- Hug- 
Key. 




Fig. S4. Multiple Switchboard for Electric Light. 

In Multiple Switchboards for the Electric Light 
or Distributing Switches, spring-jack contacts are 
connected with the terminals of different circuits, 



Boa.] 



52 



[Bod. 



and plug switches with the dynamo terminals. 
By these means, any dynamo can be connected 
with any circuit, or a number of circuits can be 
connected with the same dynamo, or a number 
of separate dynamos can be placed in the same 
circuit without interference with the lights. 



Board, Switch 



-A board provided 




with a switch or switches, by means of which 
electric circuits connected therewith may be 
opened, closed, or interchanged. 

Board, Switch, Telegraphic — A 

device employed at a telegraph station by 
means of which any one of a number of tele- 
graph instruments, in use at that station, may 
be placed in or removed from any line con- 
nected with the station, or by means of which 
one wire may be connected to another. 

The ability to readily connect one wire with 
another is of use in case of interruption to tele- 
graph lines, in which case a through circuit may 
be made up of sections of 
different circuits. 

In the switchboard shown 
in Fig. 55, the upper left- 
hand binding-post is con- 
nected to earth; the four 
remaining binding - posts 
are connected to two sepa- 
rate instruments— the sec- 
ond and third from the top to one instrument, 
and the fourth and fifth to another instrument. 
The four posts at the top of the figure are con- 
nected to two lines running east and west. 

Various connections are made by the insertion 
of plug keys in the various openings. 

Board, Switch, Trunking — A 

switchboard in which a few subscribers only 
are connected with the operator, thus enabling 
him to obtain any other subscriber by means 
of trunk wires extending to the other sections. 
(See Wire, Trunk?) 

Boat, Electric — A boat provided 

with electric motive power. 

Electric power has been applied both to ordi- 
nary vessels and to submarine torpedo boats. 

Boat, Submarine Electric A boat 

capable of being propelled and steered while 
entirely under water. 

The motive power of such boats is generally 



j-j". Telegraphic 
Switchboard. 



electricity. The requisite buoyancy is obtained 
by means of an air chamber. Artificial ventila- 
tion is maintained, the fresh air requisite for 
breathing being derived from a compressed air 
cylinder. 

Boat, Torpedo —A boat used for 

carrying and discharging torpedoes. (See 
Torpedo?) 

Bobbin, Electric An insulated coil 

of wire for an electro-magnet. 

Body, Charged A body containing 

an electric charge. 

Charges are bound or free. (See Charge,, 
Bound. Charge, Free. 1 ) 

Body, Electrified — A body con- 
taining an electric charge. 

Body, Buman, Resistance of — 



The resistance which the human body offers to- 
the passage of an electric current. 

The resistance of the human body to the passage - 
of a current varies with the time. The re- 
sistance rapidly decreases after a short time. 

" The resistance diminishes because of the con- 
duction of water in the epidermis under the action 
of the constant current and the congestion of the 
cutaneous blood vessels in consequence of the 
stimulation. ' ' ( Landois and Stirling. ) 

The resistance also varies markedly with the 
condition of the surface, the condition of the skin, 
and with the shape, area, position and material 
of the electrodes by which the current is led into 
and carried out of the parts. It very seldom is 
less than 1,000 ohms under the most favorable 
conditions, and with ordinary contacts is many- 
times that amount. 

The -muscles offer nearly nine times the resist- 
ance in a direction transverse to the fibres than 
longitudinally to them. {Hermann.) 

The resistance of the epidermis is greater than 
that of any other tissue of the bo "y. 

The human body probably possesses a true 
assymmetrical resistance; that is to say, when 
taken after the current has been passing for some 
time, its resistance is different in different direc- 
tions. This variation in the apparent resistance 
is believed by some to be due to polarization 
effects. 

Body, Insulated —A body sup- 
ported on an insulator, or non-conductor o£ 
electricity. 



Bod, 



53 



[Box. 




Fig-. 56. Electric 
Body- Protector. 



Body-Protector, Electric A de- 
vice for protecting the human body against the 
accidental passage of an electric discharge. 

To protect the human body from the acciden- 
tal passage through it of dangerous electric cur- 
rents, Delany places a light, flexible, conducting 
wire, AABLL, in the posi- 
tion shown in Fig. 56, for 
the purpose of leading the 
greater part of the current 
around instead of through 
the body. The body-pro- 
tector thus provides a by- 
path, or shunt of low resist- 
ance, around the body, and 
protects it from the effects 
of an accidental discharge. 
The resistance of the con- 
tacts of the protecting conductor with the skin 
may interfere somewhat with the efficacy of the 
device. Inside insulating shoe-soles for lessening 
the danger from accidental contacts through 
grounded circuits have also been proposed. 

Boiler-Feed, Electric — A device 

for automatically opening a boiler-feed appar- 
atus electrically when the water in the boiler 
falls to a certain predetermined point. 

Boiling 1 of Secondary or Storage Cell. — 
(See Cell, Secondary, or Storage, Boiling of.) 

Bole.— A unit, seldom or never used, pro- 
posed by the British Association. 

One bole is equal to one-gramme-kine. (See 
Kine.) 

Bolometer. — An apparatus devised by 
Langley for measuring small differences of 
temperature. 

A thermal balance. (See Balance, Ther- 
mic?) 

Bombardment, Molecular — The 

forcible rectilinear projection from the nega- 
tive electrode, of the gaseous molecules of the 
residual atmospheres of exhausted vessels on 
the passage of electric discharges. (See 
Matter, Radiant, or Ultra-Gaseous) 

Bonsalite. — An insulating substance. 

Bore, Armature The space pro- 
vided between the pole pieces of a dynamo 
or motor for the rotation of the armature. 



Boreal Magnetic Pole. — (See Pole, Mag- 
netic, Boreal.) 

Bot. — A term sometimes used as a con- 
traction for Board of Trade unit of electric 
supply, or the energy contained in a current 
of 1,000 amperes flowing in one hour under a 
pressure of one volt. 

The term appears inadmissible. If used at all, 
it should be B. O. T. The usage of giving the 
names of distinguished dead electricians to new 
units is a good one, and should be followed here. 

Boucherize. — To subject to the boucheriz- 
ing process. (See Boucherizing) 

Boucherizing. — A process for the preser- 
vation of wooden telegraph poles, by inject- 
ing a solution of copper sulphate into the 
pores of the wood. (See Pole, Telegraphic) 
Bound Charge. — (See Charge, Bound) 
Box Bridge. — (See Bridge, Box) 

Box, Cable — A box placed on a 

large terminal pole and provided to receive the 
separate conductors where the air-line wires 
join a cable. 

The wires are distributed in the cable box so 
as to be readily attached to the air-line wires. 

Box, Cooling, of Hydro-Electric Ma- 
chine. — A box provided in Armstrong's 
hydro-electric machine for the steam to pass 
through before leaving the nozzle. 

In passing through the cooling -box some of the 
steam suffers condensation. The cooling-box, 
therefore, always contains some water, the pres- 
ence of which seems to be necessary to the opera- 
tion of the machine. 

Box, Distributing, of Conduit. — A name 
generally applied to a handhole of a conduit. 
(See Handhole of Conduit) 

Box, Distribution, for Arc Light Cir- 
cuits. — A device by means of which arc 
and incandescent lights may be simultane- 
ously employed on the same line from a con- 
stant-current dynamo-electric machine or 
other source of constant currents. 

A portion of the line circuit, whose difference 
of potential is sufficient to operate the electro- 
receptive device, as, for example, an incandescent 
lamp, is divided into such a number of multiple 



Box.] 



54 



[Box. 



circuits as will provide a current of the requisite 
strength for each of the devices. For example, if 
the normal current on the line is seven amperes, 
then each of the seven multiple-connected electro- 



* r ■ *"• . t ' *— — 



Fig- 57- Series- Multiple Circuit. 

receptive devices shown in Fig. 57 will have a cur- 
rent of one ampere passing through it, provided 
the resistance of each branch is the same. 

In order to protect the remaining devices from 
variations in the current on the extinguishment of 
any of the devices, automatic cut-outs are pro- 
vided, which divert the current thus cut off 
through a resistance equivalent to that of the 
device. 

A variety of distribution boxes are in use. (See 
Circuits, Varieties of.) 

Box, District-Call — A box by 

means of which an electric signal is auto- 
matically sent over a telegraphic line and 
received by an electro-magnetic device at the 
other end of the line. 




Fig. J 8. District Call Box* 

A system of district calls includes a number of 
call boxes connected by telegraphic lines with a 
central station. A wheel, or its equivalent, set in 



motion by the pulling of a lever, makes and 
breaks an electric circuit and sends over the line 
a succession of electric impulses of varying length, 
separated from one another by varying intervals 
of time. These impulses may be received at the 
central station as a series of dots and dashes, or 
may, by means of a Morse sounder, produce suc- 
cessive sounds. By pulling the lever or handle 
through different distances, different signals may 
be sent to the central station and serve as calls for 
various services, such as messenger boys, fire 
alarm, police, special, etc. 

The general appearance of a four-call district 
box is shown in Fig. 58. In order to transmit 
a call for any particular one of these four services 
the handle is pulled until it comes opposite to the 
letters indicating the required service, and is then 
released. The service required is then indicated 
at the receiving, or central station, through the 
varying signals sent over the line by the move- 
ment of the break-wheel, on the release of the 
handle. 

Box, Fire-Alarm Signal A signal 

box provided for the purpose of automatically 
sending an alarm of fire. 

The fire-alarm box shown in Fig. 59, operates 




Fig. 59. Fire- Alarm Signal-Box. 

on the same principle as the district call box. The 
movement of the handle in the direction of the 
arrow drives a wheel that makes and breaks a 
circuit at certain intervals. 

The fire-alarm signal boxes are connected 



JSox.] 



55 



[Box, 



either with a central station, or with the engine 
houses of the district in which the alarm is 
sounded, or with both. 

Box, Fire-Alarm Telegraph An 

automatic-call signal-box employed for send- 
ing - an alarm of fire to a central station. 

A form of fire-alarm telegraph box is shown in 
Fig. 60. It consists essentially of a circuit-breaker 




Fig. bo. Fire- Alar in Telegraph Box. 
that is moved by pulling down a lever. The 
release of the lever repeats the signal to the fire 
department at the central station a certain number 
of times. The box also contains a relay bell, 
lightning arrester and signal-bell key. 

Box, Fishing- A term sometimes 

used instead of junction box. (See Box, 
Junction. ) 

Box, Flush A box or space, flush 

with the surface of a road-bed, provided in a 
system of underground wires or conduits, 
to facilitate the introduction of the conduct- 
ors into the conduit, or for the examination 
of the conductors. 

Box, Fuse The box in which the 

fuse-wire of a safety-fuse is placed. 

The fuse-box should be formed of moisture- 
proof, incombustible, insulating materials. 

Box, Junction A moisture-proof 

box provided in a system of underground con- 




the feeders and the mains, and from which 
the current is distributed to the individual 
consumer. (See Feeder. Alain, Electric^) 

A form of junction box for coupling lengths of 
conductors is shown in Fig. 61. 

Box, Patrol Alarm An automatic- 
signal call-box provided for use on the out- 
side of buildings. 

The call-box is placed inside a box, the outer 
door of which is furnished with a Yale lock. 




Fig. bl. Junction Box. 

ductors to receive the terminals of the feed- 
ers, in which connection is made between 



Fig. 62. Patrol Box. 

A iorm of patrol box is shown in Fig. 62. 

Box, Resistance A box containing 

a number of separate coils of known resist- 
ances employed for determining the value of 
an unknown resistance, and for other pur- 
poses. (See Bridge, Electric, Box Form of.) 

Box-Sounding' Relay. — (See Belay, Box- 
Sounding.) 

Box-Sounding- Telegraphic Relay. — (See 
Relay, Box-Sounding Telegraphic^) 

Box, S;>lice A box provided for 

holding splice joints and loops, and so ar- 
ranged as to be readily accessible for exami- 
nation, re-arranging, cross-connecting, etc. 

Splice-boxes vary in shape and construction 
according to the purposes for which they are 
designed. 

Box, Splice, Four-way A splice- 
box piovided with four ways or tubular con- 
duits. 

Box, Splice, Two Way A splice- 



Box.J 



56 



[Bra. 



box provided with but two tubular conduits or 
ways. 

Box, Tumbling A rotating box 

in which metallic articles that are to be 
electroplated are placed so as to be polished 
by attrition against one another. 

Boxing" tlie Compass. — (See Couipass, 
Boxmg the?) 

Bracket, Lamp, Electric A de- 
vice similar to a bracket for a gas burner for 
holding or supporting an electric lamp. 



Braid, Tubular 



-A braid of fibrous 





Fig. 63. Lamp Bracket. Fig. 6 4. Lamp Bracket. 
Lamp brackets are either fixed cr movable. 




Fig. 6 J. Lanip Bracket, Movable Arms. 

Those shown in Figs. 63 and 64 are fixed. That 
shown in Fig. 65 is movable. 

Bracket, Telegraphic A support 

or cross piece placed on a telegraph pole 
for the support of the insulators of tele- 
graphic lines. 

Telegraphic insulators are supported either on 
wooden arms, or on iron or metal brackets. 

Fig. 66 shows a form of iron bracket. Fig. 6j 
shows a form of wooden arm. 





Fig. 66. Telegraphic Fig. 67. Telegraphic 

Bracket. Cress-Arm. 

Various well known modifications of these 
shapes are in common use. (For details, see Fo/e, 
Telegraphic. ) 



insulating material, woven in the form of a 
tube, and provided for drawing over a splice 
after two wires have been connected. 

Braided Wire. — (See Wire, Braided.) 

Brake, Electro-Magnetic A brake 

for car wheels, the braking power for which 
is either derived entirely from electro-magnet- 
ism, or is thrown into action by electro-mag- 
netic devices. 

Electro-magnetic car brakes are of a great va- 
riety of forms. They may, however, be arranged 
in two classes, viz. : 

(1.) Those in which magnetic adhesion, or the 
magnetic attraction of the brake to the wheels, is 
employed. 

(2.) Ordinary brake mechanism in which the 
force operating the brake is thrown into action by 
an electro-magnet. 

Brake, Friction — 



— A name some- 
times given to a Prony brake. (See Brake, 
Prony.) 

Brake, Magneto-Electric A device 

for checking the swing of a galvanometer, in 
which a slight inverse current is sent through 
the coils of the galvanometer. 

The Frey magneto- electric brake, as shown in 
Fig. 68, consists of a small coil, connected by a 




Fig. 68. Electric Brake. 

contact-key with the galvanometer terminals. A 
small adjustable magnet coil is provided for 
regulating the action of the inverse current. To 
avoid disturbance, the brake is placed at least 
4 or 5 feet from the galvanometer. Manipulation 
of the ordinary galvanometer key attains the same 
end in a much simpler manner. 

Brake, Prony A mechanical de- 
vice for measuring the power of a driving 
shaft. 



Era. 



57 



[Bre. 



An inflexible beam, Fig. 69, is provided at one 
<end with a clamping device for clamping the 
driving shaft or pulley, and at the other end A, 
with a pan for holding weights. 

If the brake be arranged as shown in Fig. 69, 
and the shaft rotate in the direction of the arrow, 
the tendency will be to carry the beam around 
with the shaft, placing it at some given moment 



£ 



ca? 




Fig. 6q. Prony Brake, 
in the position shown by the dotted line. If a 
sufficiently heavy weight be placed at x, in a pan 
hung at A, the beam will assume a position ver- 
tically downwards. If, however, the torque, or 




Fig. 70. Prony Brake. 

twisting force of the driving shaft, be balanced by 
the weight, the bar will remain horizontal. The 
power can then be calculated by multiplying the 
weight in pounds by the circumference in feet of 
the circle of which the bar is a radius, and this 
product by the number of turns of the driving 
shaft per minute. The product will be the num- 

. |. 





Fig. 7 7". Prony Brake. 
ber of foot-pounds per minute, and, when divided 
by 33,000, will give the horse-power. 

Some modified forms of the Prony brake are 
shown in Figs. 70 and 71. 

A simple form of brake consists of a cord passed 
over the pulley of the machine to be tested. A 
weight is hung at one end of the cord. The other 



end of the cord is attached to the top of a spring 
balance, the other end of which is fastened to the 
floor. A reading of the spring balance is taken 
while the pulley is at rest and when it is in motion, 
and the result calculated. 

Branch. — A term applied to any principal 
distributing conductor from which outlets 
are taken or taps made. 

Branch-Block. — (See Block, Branch?) 

Branch Conductors. — (See Conductor, 
Branch?) 

Branch Fuse. — (See Fuse, Branch.) 

Branch, Sub A distributing- con- 
ductor taken from a branch. 

Branding", Electric — A process 

whereby the branding tool is heated by elec- 
trical incandescence instead of by ordinary 
heat. 

The branding tool consists essentially of a small 
transformer with devices for regulating the cur- 
rent strength by switches and choking coils. 

Brassing, Electro Coating a sur- 
face with a layer of brass by electro-plating. 
(See Plali?ig, Electro?) 

The plating bath contains a solution of copper 
and zinc ; a brass plate is used as an anode. 

Break. — A want of continuity in a circuit. 

Break, Circuit Loop A device for 

introducing a loop in any part of a line 
circuit. 

A form of circuit loop-break is shown in Fig. 72. 




Fig. 7 2. Circuit Loop Break. 
It consists essentially of a rigid frame with two 
porcelain or other suitable insulators for the sup- 
port of the loop wires. 



Bre.] 



58 



[Bri, 



Break-Down Switch. — (See Switch, Break- 
Down) 

Break-Induced Current. 1 — (See Current, 
Break-Induced) 

Break, Mercury A form of circuit 

breaker operated by the removal of a conduc- 
tor from a mercury surface. 

Mercury breaks assume a variety of forms. One 
end of the circuit is connected with the mercury, 
and the other with the conductor. 

Break Shock. — (See Shock, Break) 

Breaker, Circuit Any device for 

breaking a circuit. 

Breaking' the Primary.— (See Primary, 
Breaking the.) 

Breaking- Weight of Telegraph Wires. — 
(See Wires, Telegraph, Breaking Weight 
of.) 

Breath Figures.— (See Figures, Breath.) 

Breeze, Electric A term some- 
times employed in electro-therapeutics for a 
brush discharge. 

One of the electrodes, consisting of a single 
point or a number of points, is held near the 
parts to be treated so that the con vective discharge 
is received thereon. The other electrode is con- 
nected to the body of the patient. 

Breeze, Electro-Therapeutic An 

electric breeze. (See Breeze, Electric) 

Breeze, Head, Electro-Therapeutic 

— A form of electric convective discharge, 
or electric breeze, applied to the head. (See 
Breeze, Electric) 

Breeze, Static An electric breeze 

obtained by the convective discharge of an 
electrostatic charge. 

Bridge-Arms. — (See Arms, Bridge or 
Balance) 

Bridge, Box A box of resistance 

coils so arranged as to be capable of being 
used directly as a Wheatstone electric balance. 
(See Bridge, Electric, Box Form of) 

The commercial form of Wheatstone's 
balance. 

Bridge, Electric — A device for 

measuring the value of electric resistances. 



The electric bridge is also called the Electric 
Balance. 

This is called a bridge because the wire M, G, 
N, bridges or joins points of equal potential. 

A, B, C and D, Fig. 73, are four electric re- 
sistances, any one of which can be determined in 
ohms, provided the absolute value of one of the 
others, and the relative values of any two of the 
remaining three are known in ohms. 

A voltaic battery, Zn C, is connected at Q 
and P, so as to branch at P, and again unite at 




Zn' C 
Fig. 73. Electric Balance. 

Q, after passing through the conductor D C, and 
B A. 

A sensitive galvanometer, G, is connected at 
M N, as shown. 

The passage of a current through any resistance 
is attended by a fall of potential proportional to 
the resistance. (See Potential, Electric.) If, then, 
the resistances A, C and B, are so proportioned 
to the value of the unknown resistance D, that no 
current passes through the galvanometer G, the 
two points, M and N, in the two circuits, QMP 
and Q N P, are at the same potential. That is to 
say, the fall of potential along QMP and Q N P, 
at the points M and N, is equal. Since the fall 
of potential is proportional to the resistance, it 
follows that 

A : B : : C : D, 
or A X D = B X C, 

C. 



D -G) 



If then we know the values of A, B and C, the 
value of D, can be readily calculated. 

By making the value _, some simple ratio, the 

value of D, is easily obtained in terms of C. 

The resistances A, B and C, may consist of 
coils of wire whose resistance is known. To 
avoid their magnetism affecting the galvanometer 
needle during the passage of the current through 
them, they should be made of wire bent into two- 



Bri.] 



59 



[Bri. 



parallel wires and wrapped in coils called resist- 
ance coils; or a resistance box may be used. (See 
Coil, Resistance. Box, Resistance.) 

There are two general forms of Wheatstone's 
Bridge, the box form, and the sliding form. 

Bridge, Electric, Arms of The 

resistances of an electric bridge or balance. 
(See Bridge, Electric?) 

Bridge, Electric, Box Form of 

A commercial form of bridge or balance in 
which all the known arms or branches of the 
bridge, except the unknown arm, consist of 
standardized resistance coils, whose values are 
given in ohms. (See Coil, Resistance?) 

The box form of bridge or balance is shown in 




Fig. 7 4. Box Balance. 

perspective in Fig. 74, and in plan in Fig. 75. 
The bridge arms, corresponding to the resistances 



x 1000 100 1 9 1 ' 100 10 00 




Fig-. 7 J. Box Balance. 

A and B, of Fig. 73, consist of resistance coils of 
10, 100 and 1,000 ohms each, inserted in the 
arms q z, and q x, of Fig. 75. These are 
called the proportional coils. The arm corre- 
sponding to resistance C, of Fig. 73, is composed 
of separate resistances of I, 2, 2, 5, 10, 10, 20, 50, 
ico, 100, 200, 500, i,oco, 1,000, 2.000 and 5,000 
ohms. In some forms of box bridges additional 
decimal resistances are added. 

The resistance coils are wound, as shown in 
Fig. 76, after the wire has been bent on itself in 
the middle. This is done in order to avoid the 
effects of induction, among which are a disturb- 
ing action on a galvanometer used near them, 
and the introduction of a spurious resistance in 
the coils themselves. (See Resistance, Spurious.) 



To avoid the effects of changes of resistance oc- 
casioned by changes of temperature, the coils are 
made of German silver, or, preferably, of alloys 
called Platinoid or Platinum silver. Even when 
these alloys are used, care should be taken not to 
allow the currents to pass continuously through 
the resistance coils longer than a few moments. 

The coils, C, C, are connected with one another 
in series by soldering their ends to the short 




Resistance Coils. 



thick pieces of brass, E, E, E, Fig. 76. On the in- 
sertion of the plug-keys, at S, S, the coils are cut- 
out by short-circuiting. Care should be taken to 
see that the plug-keys are firmly inserted and free 
from grease or dirt, as otherwise the coil will not be 
completely cut out. As each plug-key is inserted 
it should be turned slightly in the opening, so 
as to insure good contact. 

The following are the connections, viz.: The 
galvanometer is inserted between q and r, Fig. 77, 




Electric Balance. 



the unknown resistance between z and r; the bat- 
tery is connected to x and z. A convenient pro- 
portion being taken for the value of the propor- 
tional coils, resistances are inserted in the arm C, 
until no deflection is shown by the galvanometer 
G. The similarity between these connections and 
those shown in Fig. 75 will be seen from an 
inspection of Fig. 77. The arms, A and B, corre- 
spond to q x and q z, of Fig. 75; C, to the arm. 



EiL] 



60 



[Bri. 



x r, Fig. 75 ; and D, to the unknown resistance. 
We then have as before: 

A:B::C:D,orAxD = BxC. .■.D = /!V. 

The advantage of the simplicity of the ratios, A 
and B, or 10, ioo and 1,000 of the bridge box, 
will therefore be manifest. The battery terminals 
may also be connected to q and r, and the gal- 
vanometer terminals to x and z, without disturb- 
ing the proportions. 

Bridge, Electric, Commercial Form of 

A name sometimes given to the box 

form of Wheatstone's electric balance. (See 
Bridge, Electric, Box Form of.) 

Bridge, Electric Duplex An ar- 
rangement of telegraphic circuits in the form 
of a Wheatstone electric bridge for the pur- 
poses of duplex telegraphy. (See Teleg- 
raphy, Duplex, Bridge Method of.) 

Bridge, Electric, Proportionate Arms 

of (See Arms, Proportionated) 



Bridge, Electric, Slide-Form of 



A balance in which the proportionate arms of 
the bridge are formed of a single thin wire, of 
uniform diameter, generally of German silver, 
of comparatively high resistance. The length 
of this wire is usually one metre ; hence this 
apparatus is often called the metre bridge. 

A Sliding Contact Key slides over the wire; one 
terminal of the key is connected with the galva- 
nometer and the other with the wire when the key 
is depressed. As the wire is of uniform diameter 
the resistances of the arms, A and B, Fig. 78, will 




Fig. 78. Slide Bridge. 

be directly proportional to the lengths. A scale 
placed near the wire serves to measure these 
lengths. A thick metal strip connected with the 
slide wire has four gaps at P, Q, R and S. 

When in ordinary use, the gaps at P and S, are 
either connected by stout strips of conducting ma- 
terial or by known resistances, in which latter case 
they act simply as ungraduated extensions of the 
slide wire, and, like lengthening the slide wire, 
increase the sensibility of the instrument. 



The unknown resistance is then inserted in the 
gap at Q, and a known resistance, generally the 
resistance box, in that at R. The galvanometer 
has one of its terminals connected to the metal 
strip between Q and R, and its other terminal to 
the sliding key. The battery terminals are con- 
nected to the metal strips between P and Q, and 
R and S, respectively. 

These connections are more clearly seen in the 
form of bridge shown in Fig. 79. The slide wire, 
w w, consists of three separate wires each a metre 




Fig. fg. Slide Form of Bridge. 

in length, so arranged that only one wire, or two 
in series, or all three in series, can be used. Mat- 
ters being now arranged as shown, the sliding 
key is moved until no current passes through the 
galvanometer when the key is depressed. 

The slide form of bridge is not entirely satis- 
factory, since the uncertainty of the spring-con- 
tact causes a lack of correspondence between the 
point of contact and the point of the scale on 
which the index rests. 

The loss of uniformity in the diameter of the 
wire, due to constant use, causes a lack of corre- 
spondence between the resistance of the wire and 
its length. With care, however, very accurate 
results can be obtained by the slide form. 

Bridge, Inductance An appara- 
tus for measuring the inductance of a circuit 
similar to a Wheatstone bridge. (See Indue- 
tance?) 

Professor Hughes employed an inductance 
bridge of the following description: 

Four resistances, Q, S, R and P, arranged as 
shown in Fig. 80, form the bridge. The re- 
sistances, Q, S and R, consist of sections of Ger- 
man silver wire, one metre in length, each of 
the resistance of 4 ohms. P, is a coil of wire pos- 
sessing sensible inductance. The object of the 



Bri.] 



61 



[Bri. 



bridge is to measure the value of this inductance. 
I, is an interrupter placed in the circuit of the 
battery B. 

Suppose the interrupter, I, be placed in the tele- 
phone circuit between T and c. By shifting the 
sliding contact so as to alter the value of R, a bal- 




Fig. So 



ance can be effected and silence obtained in the 
telephone. 

Now remove the interrupter and place it in the 
battery circuit between b and a, as shown in Fig. 
80. If now, the interrupter, I, be made to rapidly 
interrupt the battery current, this balance is 
destroyed, and cannot be again obtained by any 
variation in the value of the resistance, R. 

The reason of this is evident. On the closing 
or opening of the battery current, the inductance 
of P, produces a counter electromotive force in 
P, which produces differences of potential between 
a and c. If an attempt be made to prevent this, 




Fig. St. Hughes' Inductance Bridge. 

by altering the value of R, the steady balance is 
destroyed, and the telephone will be traversed by 
a current during the time the currents have be- 
come steady. In order to obtain a balance 
during rapid alternations of the battery current, 
Professor Hughes placed a pair of mutually in- 



ductive coils in the battery and the telephone 
circuits, as shown in Fig. 81. 

The resistances, Q, S, R and P, are the same 
as already described. The mutually inductive 
coils, M x and M 2 , are placed respectively in the 
telephone and batttry circuits in the manner 
shown. The coil M 2 , in the battery circuit is 
fixed, while that in the telephone circuit is so 
arranged that it can be maintained, with its centre 
coincident with that of M 2 , while its axis can be 
placed at any desired angle with M 3 . When the 
axes of the coils are at right angles, the inductance 
is zero. When they are co-linear, the inductance 
is at its maximum. 

When the coils M 1? and M 8 , are in any inter- 
mediate position, the inductive electromotive 
force produced in the telephone circuit can, if 
the value of R, be changed, be made to balance 
the impulsive electromotive force due to the in- 
ductance of P, and the value of this latter can, 
therefore, be inferred. 



Bridge, Magnetic 



-An apparatus in- 



vented by Edison for measuring magnetic 
resistance, similar in principle to Wheatstone's 
electric bridge. 

The magnetic bridge is based on the fact that 
two points at the same magnetic potential, when 
connected, fail to produce any action on a mag- 
netic needle. The magnetic bridge consists, as 
shown in Fig. 82, of four arms or sides made of 




Fig. 82 



ic Bridge. 



pure, soft iron. The poles of an electro-magnet 
are connected to projections at the middle of 
the short side of the rectangle. By this means 
a difference of magnetic potential is main- 
tained at these points. The two long sides are 
formed of two halves each, which form the four 
arms of the balance. Two of these only are 
movable. 

Two curved bars of soft iron, of the same area 
of cross-section as the arms of the bridge, rest on 
the middle of the long arms, in the arched shape 
shown. Their ends approach near the top of the 



BrL] 



62 



LBru. 



arch within about a half inch. A space is hol- 
lowed out between these ends, for the reception of 
a short needle of well-magnetized hardened steel, 
suspended by a wire from a torsion head. 

The movements of the needle are measured on 
a scale by a spot of light reflected from a mirror. 

The electro-magnet maintains a constant dif- 
ference of magnetic potential at the two shorter 
ends of the rectangle. If, therefore, the four 
bars, or arms of the bridge, are magnetically 
identical, there will be no deflection, since no 
difference of potential will exist at the ends of the 
bars between which the needle is suspended. If, 
however, one of the bars or arms be moved even 
a trifle, the needle is at once deflected, the motion 
becoming a maximum when the bar is entirely 
removed. If replaced by another bar, differing 
in cross-section, constitution, or molecular struc- 
ture; the balance is likewise disturbed. 

The magnetic bridge is very sensitive. It was 
designed by its inventor for testing the magnetic 
qualities of the iron used in the construction of 
dynamo-electric machines. 

Bridge Method of Duplex Telegraphy. — 

(See Telegraphy, Duplex, Bridge Method 
of) 

Bridge Method of Quadruplex Teleg- 
raphy. — (See Telegraphy, Quadruplex, 
Bridge Method of.) 

Bridge, Metre A slide form of 

Wheatstone's electric bridge, in which the 
slide wire is one metre in length. (See 
Bridge, Electric, Slide Form of.) 

Bridge, Resistance A term some- 
times applied to an electric bridge or balance. 
(See Bridge, Electric.) 

Bridge, Reversible A bridge or 

balance so arranged that the proportionate 
coils can be readily interchanged, thus per- 
mitting the bridge coils to be readily tested by 
reversing. 

Bridge, Wheatstone's Electric 

A name given to the electric bridge or balance. 
(See Bridge, Electric.) 

Bridges. — Heavy copper wires suitably 
shaped for connecting the dynamo-electric 
machines in an incandescent light station to 
the bus-rods or wires. 



Bright Dipping.— (See Dipping, Bright) 
Bright Dipping Liquid. — (See Liquid* 
Bright Dipping) 

Britannia Joint. — (See Joint, Britannia) 
Broken Circuit. — (See Circuit, Broken) 

Bronzing, Electro Coating a sur- 
face with a layer of bronze by electro-plating.. 
(See Plating, Electro) 

The plating bath contains a solution of tin and 
copper. 

Brush-and-Spray Discharge. — (See Dis- 
charge, Brush-and-Spray) 

Brush Discharge. — (See Discharge* 
Brush) 

Brush Electrode. — (See Electrode, Brush) 

Brush, Faradic An electrode in 

the form of a brush employed In the medical 
application of electricity. 

The bristles are generally made of nickelized 
copper wire. 

Brush-Holders for Dynamo-Electric Ma- 
chines. — Devices for supporting the collecting 
brushes of dynamo-electric machines. 

As the brushes require to be set or placed on 
the commutator in a position which often varies 
with the speed of the machine, and with changes 
in the resistance of the external circuit, all brush- 
holders are provided with some device for moving 
them concentrically with the commutator cylin- 
der. 

Brush Rocker. — (See Rocker, Brush) 

Brush, Scratch A brush made 

of wire or stiff bristles, etc., suitable for clean- 
ing the surfaces of metallic objects before 
placing them in the plating bath. 

Scratch brushes are made of various shapes and' 
are provided with wires or bristles of varying 
coarseness. 

Some forms of scratch and finishing brushes 
are shown in Fig. 83. They are circular in outline 




Fig. 83. Scratch Brushes. 

and are adapted for use in connection with a 
lathe. 



Bru.] 



63 



[Bui. 



Brush, Scratch, Circular —A 

scratch brush of a circular shape, so fitted as 
to be capable of being placed in a lathe and 
set in rapid rotation. 

Brush, Scratch, Hand —A scratch 

brush operated by hand, as distinguished 
from a circular scratch brush operated by a 
lathe. 

Brushes, Adjustment of Dynamo-Electric 

Machines Shifting the brushes into 

the required position on the commutator 
cylinder, either non-automatically by hand, or 
automatically by the current itself. (See 
Regulation, Automatic, of Dynamo-Electric 
Machines) 

Brushes, Carbon, for Electric Motors 

Plates of carbon for leading current 

to electric motors. (See Brushes of Dynamo- 
Electric Machine) 

These are generally known simply as brushes. 

Brushes, Collecting, of Dynamo-Electric 

Machine Conducting brushes which 

bear on the commutator cylinder, and take off 
the current generated by the difference of 
potential in the armature coils. (See Brushes 
of Dynamo-Electric Machine) 

Brushes, Lead of The angle through 

which the brushes of a dynamo-electric ma- 
chine must be moved forward, or in the 
direction of rotation, in order to diminish 
sparking and to get the best output from 
the dynamo. 

The necessity for the lead arises from the coun- 
ter magnetism or magnetic reaction of the arma- 
ture, and the magnetic lag of its iron core. (See 
Lead, Angle of.) 

The position of the brushes on the commutator 
to insure the best output is practically the same 
in a series dynamo for any current strength. 
In shunt and compound dynamos it varies with 
the lead. 

Brushes of Dynamo-Electric Machine.— 

Strips of metal, bundles of wire, slit plates of 
metal, or plates of carbon, that bear on the 
commutator cylinder of a dynamo-electric 
machine, and carry off the current generated. 
Rotary brushes consisting of metal discs are 
sometimes employed. Copper is almost univer- 




Fig. 84. Brushes, 



sally used for the brushes of dynamo-electric 
machines. Carbon brushes are often used for 
dynamo-electric motors. 

The brush shown at B, Fig. 84, is formed of 
copper wires, soldered 
together at the non- 
bearing end. A copper 
plate, slit at the bear- 
ing end, is shown at C, 
and bundles of copper 
plates, soldered together 
at the non-bearing end, 
are shown at D. 

The brushes should 
bear against the com- 
mutator cylinder with 
sufficient force to pre- 
vent jumping, and con- 
sequent burning, and 
yet not so hard as to 
cause excessive wear. 

Brushes, Rotating, of Dynamo-Electrie 

Machines Discs of metal, employed 

in place of the ordinary brushes for carry- 
ing off the current from the armatures of 
dynamo-electric machines. 

Brushing-, Scratch Cleansing the 

surface of an article to be electroplated, by 
friction with a scratch brush. 

Scratch brushing is generally done with the 
brushes wet by various solutions. 

Buckling". — Irregularities in the shape of 
the surfaces of the plates of storage cells, fol- 
lowing a too rapid discharge. 

Bug. — A term originally employed in quad- 
ruplex telegraphy to designate any fault in 
the operation of the apparatus. 

This term is now employed, to a limited extent, 
for faults in the operation of any electric appa- 
ratus. 

Bug-Trap.— A device employed to over- 
come the " bug " in quadruplex telegraphy. 

Bulb, Lamp — The chamber or 

globe in which the filament of an incan- 
descent electric lamp is placed. 

The chamber or globe of a lamp must be of 
such construction as to enable the high vacuum 
necessary to the operation of the lamp to be main- 
tained. 



Bun.] 



64 



[Bur. 



Bunched Cable.— (See Cable, Bunched.) 
Bunched Cable, Straightaway 

(See Cable, Bunched, Straightaway) 

Bunched Cable, Twisted — (See 

Cable, Bunched, Twisted.) 

Bnnsen Voltaic Cell.— (See Cell, Voltaic, 
Bunsen's.) 

Buoy, Electric A buoy on which 

luminous electric signals are displayed. 

Burglar Alarm.— (See Alarm, Burglar?) 

Burglar Alarm Annunciator. — (See An- 
nunciator, Burglar Alarm) 

Burglar Alarm Contacts. — (See Contacts, 
Burglar Alarm?) 

Burglar Alarm, Tale Lock Switch for — 
— (See Alarm, Yale-Lock-Switch Burglar?) 

Burner, Argand Electric An ar- 
gand gas-burner that is lighted by means of 
an electric spark. 

The argand electric burner assumes a variety 
of forms, such as the plain-pendant, the ratchet- 
pendant and the automatic. They are also used 
in systems of multiple gas lighting. 

Burner, Argand Electric, Automatic 

— An argand burner arranged for automatic 
electric lighting. (See Burner, Automatic- 
Electric?) 

Burner, Argand Electric, Hand-Lighter 

— A plain-pendant electric burner 

adapted for lighting an argand gas-burner. 
(See Burner, Plain-Pendant Electric?) 

Burner, Argand-Electric, Plain-Pendant 

— A plain-pendant electric burner 

adapted for lighting an argand gas burner. 
(See Burner, Plain-Pendant Electric.) 

Burner, Argand-Electric, Ratchet-Pend- 
ant A ratchet-pendant electric burner 

adapted for lighting an argand gas-burner. 
(See Burner, Ratchet-Pendant Electric?) 

Burner, Automatic-Electric An 

electric device for both turning on the gas 
and lighting it, and turning it off, by alter- 
nately touching different buttons. 

The gas-cock is opened or closed by the motion 
of an armature, the movements of which are con- 
trolled by two separate electro-magnets. One 
push-button, usually a white one, turns the gas on 




by energizing one of the electro-magnets and, 
at the same time, lights it by means of a suc- 
cession of sparks from a spark coil. Another 
push-button, usually a black one, turns the gas 
off by energizing the other electro-magnet. 
The turning on or off of the gas is accom- 
plished by positive 
motions. Automatic 
burners are also made 
with a single button. 

An Argand Electric 
Burner is shown in 
Fig. 85. 

Burner, Electric 

Candle — A 

device for electri- 
cally lighting a gas 
jet in a burner sur- 
rounded by a por- 
celain tube in imita- 
tion of a candle. 

Electric candle bur- 
ners are either simple 
or ratchet candle bur- 
ners. 

Burner, Hand- 
Lighting Electric 
A name sometimes applied to a plain- 
pendant electric burner. (See Burner, Plain- 
Pendant Electric.) 

Burner, Jump-Spark A term 

sometimes applied to a gas burner in which 
the issuing gas is ignited 
by a spark that jumps be- 
tween the metallic points \X ^J® 
placed on it. 

Jump-spark burners are 
used in systems of multiple 
gas lighting. (See Light- 
ing, Electric Gas.) 

Burner, Plain-Pen- 
dant Electric A 

gas - burner provided 

with a pendant for the 

purpose of lighting the 

gas by means of a spark, F ig. 86. Plain-Pendant 

after the gas has been Burner. 

turned on by hand. 

The gas is first turned on by hand at the ordi- 



Fig. Sj. Argand Electric 
Burner. 




Bur.] 



65 



[But. 



nary key, and is then lighted by pulling the pend- 
ant C, Fig. 86. A spark from a spark coil ignites 
the gas. 

This is sometimes called an electric hand- 
lighting burner. 

Burner, Ratchet-Pendant Candle Elec- 
tric A burner for both lighting and 

extinguishing a candle gas jet. 

Burner, Ratchet-Pendant Electric 

— A gas-burner in which one pulling of a 
pendant turns on the gas and ignites it by 
means of an electric spark from a spark coil, 
and the next pulling of the pendant turns off 
the gas. 

A ratchet-wheel and pawl are operated by the 
motion of the pendant. The first pull of the 
pendant chain moves the ratchet so as to open a 
four-way gas cock, and at the same time light 
the gas at the burner tip by a wipe-spark from a 
spark coil. On the next pull ot the pendant, the 
four- way cock is turned so as to turn off the g?s. 
Alternate pulls, therefore, light and extinguish 
the gas. 

Burner, Simple Candle Electric 

A plain-pendant electric burner. (See Bur- 
ner, Plain Pendant Electric.) 



Thumb-Cock Electric 

gas- 



Burner, 

An electric 
burner, in which 
the turning of an 
ordinary thumb- 
cock turns on the 
gas, and ignites it 
by a spark pro- 
duced by a wiping 
contact actuated 
by the motions of 
the thumb-cock. 
A form of thumb- 
cock burner is 
shown in Fig. 87. 

Burner, Vi- 
brating - E 1 e c - 

trie — An Fig. 87. Ihumb-Cock Burner. 

electric gas-burner in which the gas is lighted 
after it is turned on by hand, by means of the 
spark from a spark coil produced on the rapid 




making and breaking of the circuit by a 
vibrating contact. 

The vibrating- electric burner has a single elec- 
tro-magnet. It is operated by means of a button 
or switch, and may be used on single lights or on 
groups of lights. It bears the same relation to 
the automatic burner that the plain-pendant 
burner does to the ratchet burner. 

Burnetize. — To subject to the Burnetizing 
process. (See Burnetizing.) 

Burnetizing. — A method adopted for the 
preservation of wooden telegraph poles by 
injecting a solution of zinc chloride into the 
pores of the wood. (See Pole, Telegraphic) 

Burning at Commutator of Dynamo. — 

An arcing at the brushes of a dynamo-elec- 
tric machine, due to their imperfect contact, 
or improper position, which results in loss of 
energy and destruction of the commutator 
segments. 

Bus. — A word generally used instead of 
omnibus. (See Omnidus.) 

Bus-Bars. — (See Bars, Bus.) 

Bus-Rod Wires. — (See Wires Bus-Rod.) 

Bus-Wire. — (See Wire, Bus.) 

Butt Joint. — (See Joint, Butt) 

Button, Carbon — A resistance of 

carbon in the form of a button. 

A button of carbon is used as an electric resist- 
ance in a variety of apparatus; its principal use, 
however, is in the transmitting instrument of the 
electric telephone. In the telephone transmitter, 
the button is so placed between contact-plates that 
when the plates are pressed together by the 
sound-waves, the electrLal resistance is decreased 
by a decrease in the thickness of the carbon button, 
an increase in its density, and an increase in the 
number of points where the carbon touches the 
plates. Rheostats, or resistances, have been 
made by the use of a number of carbon buttons or 
discs piled one on another and placed in a glass 
tube. Discs of carbonized cloth form excellent 
resistances ior such purposes. 

Button, Press A push button. 

(See Button, Push) 

Button, Push A device for closing 



But.] 



66 



[Cab. 



*n electric circuit by the movement of a Buzzer, Electric — A call, not as 

button. loud as that of a bell, produced by a rapid 

A button, when pushed by the hand, closes the 





Fig. 88. Push Button. Fig. 8g. Fush Button. 

contact, and thus completes a circuit in which 
some electro-receptive device is placed. This 
circuit is opened by a spring, 
on the removal of the pressure. 
Some forms of push-buttons are 
shown in Figs. 88, 89 and 90. 

A floor-push for dining-rooms 
and offices is shown in Fig. 
90. 

Fig. 88 shows the general 
appearance of an ordinary bell- 
push. The arrangement of the 
interior spring contacts will be 
understood by an inspection of Fig. 91 




Fig. qo. Floor 
Push. 




Fig. Q f. Spring Contact of Bell Push. 

automatic make-and-break. (See Make-and- 
Break, Automatic?) 

The buzzer is generally pk ced inside a resonant 




Fig. Q2. Buzzer. 

case of wood in order to strengthen the sound by 
resonance. A form of buzzer is shown in Fig. 92. 



€. — An abbreviation for centigrade. 

"^hus, 20 degrees C. means 20 degrees of the 
centigrade thermometric scale. (See Scale, Cen- 
tigrade Thermometer.) 

C. — A contraction for current. 

Generally a contraction for the current in 

amperes, as C = ^. 

C. C. — A contraction for cubic centimetre. 
(See Weights and Measures, Metric System 
of) 

C. G. S. Units.— A contraction for centi- 
timetre-gramme-second units. (See Units, 
Centimetre-Gramme- Second) 



C. P. — A contraction for candle power. 
(See Candle, Standard) 

Cable. — An electric cable. (See Cable, 
Electric) 

Cable. — To send a telegraphic dispatch, 
by means of a cable. 

Cable, Aerial A cable suspended 

in the air from suitable poles. 

Cable, Anti-Induction, Waring 

A form of anti-induction cable. 

In the Waring an ti- induction cable the separate 
conductors are covered with a fibrous insulator, 
from which all air and moisture is expelled, and 
the fibre then saturated with an insulating ma- 



Cab.] 



67 



[Cab. 



terial called ozite. The conductors are then pro- 
tected from the inductive effects of neighboring 
conductors by a continuous sheath of lead alloyed 
with tin. 

Where the cables are bunched, the bunches 
are sometimes again surrounded by insulating 
material, and the whole then covered by a con- 
tinuous lead sheathing ; generally, however, the 
separately insulated conductors are bunched, 
and then covered by a single sheathing of lead 
alloyed with tin. 

Cable, Armature of — . The armor of 

a cable. (See Armature of a Cabled) 

Cable, Armor of The protecting 

sheathing or metallic covering on the outside 
of a submarine or other electric cable. 

Cable, Armored An electric cable 

provided, in addition to its insulating coat- 
ing, with a protective coating or sheathing, 
generally of metal tubing or wire. 

Cable-Box.— (See Box, Cabled 

Cable, Bunched A cable contain- 
ing more than a single wire or conductor. 

Some forms of bunched, lead-covered cables, 
are shown in Fig. 93. 



Fig. 93. Bunched Cables. 

Cable, Bunched, Straightaway 

A bunched cable the separate conductors of 
which extend in the direction of the length of 
the cable without any twisting, being placed 
in successive layers. 

In arranging the separate conductors in suc- 
cessive layers an advantage is gained in testing 
for a given wire in order to make a loop, splice, 
or branch with the next adjoining section. This is 
rendered still easier by giving the conductors 
of the successive layers some distinctive form of 
braiding in the fibrous insulating material, or 
some distinctive color. 

Cable, Bunched, Twisted —A 

bunched cable, the separate conductors of 
which are twisted-pairs placed in successive 
layers. 



Each twisted-pair of a bunched cable acts as a 
metallic circuit, and, moreover, possesses the ad- 
vantage of avoiding the ill effects of induction, so 
disadvantageous in telephone circuits. 

In laying up the twisted-pairs in successive 
layers in a bunched cable, the direction of twist- 
ing is reversed in each successive layer. This 
form is especially desirable on all long cable lines. 

In the case of twi-ted cables for telephone lines, 
the twists are sometimes made as frequent as one 
in every three or four inches. In such cases the 
cross-talk of induction is inappreciable. 

Cable, Capacity of The quantity 

of electricity required to raise a given length 
of a cable to a given potential, divided by the 
potential. 

The amount of charge for a given potential 
that any single conductor will take up with 
the rest of the conductors grounded. (See 
Capacity, Electrostatic) 

The ability of a wire or cable to permit a 
certain quantity of electricity to be passed 
into it before acquiring a given difference of 
potential. 

Before a telegraph line or cable can transmit a 
signal to its further end, its difference of potential 
must be raised to a definite amount dependent on 
the character of the instruments and the nature of 
the system. 

The first effect of electricity being passed into a 
line is to produce an accumulation of electricity 
on the line, similar to the charge in a condenser. 
Cables especially act as condensers, and fiom the 
high specific inductive capacity of the insulating 
materials employed, permit considerable induc- 
tion to take place between the core and the 
metallic armor or sheathing, or the ground. 

The capacity of a cable depends on the capacity 
of the wire ; i. e., on its length and surface, on 
the specific inductive capacity of its insulation, 
and its neighborhood to the earth, or to other 
conducting wires, casings, armors, or metallic 
coatings. Submarine or underground cables 
therefore have a greater capacity than air lines. 

This accumulation of electricity produces a re- 
tardation in the speed of signaling, because the 
wire must be charged before the signal is received 
at the distant end, and discharged or neutralized 
before a current can be sent in the reverse direc- 
tion. This latter may be done by connecting 
each end to earth, or by the action of the reverse 
current itself. 



Cab.J 



08 



[Cab. 



The smaller the electrostatic capacity of a cable, 
therefore, the greater the speed of signaling. (See 
Retardation. ) 

The capacity of a cable is measured in micro- 
farads. (See Farad, Micro.) 

Cable Clip.— (See Clip, Cable.) 

Cable-Core.— (See Core of Cabled 

Cable, Core-Ratio of The ratio be- 
tween the diameter of the insulation of a cable 
and the mean diameter of the strand. 

D 

The core- ratio is represented by -p where D, 

is the diameter of the insulation, and d, the mean 
diameter of the strand. Should the extreme 
diameter of the strand of a cable be used in cal- 
culations for insulation resistance, inductive capa- 
city, etc., erroneous values would be obtained. 
The measured diameter of the copper conductor 
is consequently decreased some five per cent., and, 
in this way, correct values are approximately 
obtained. — [Clark 6° Sabine.) 

Cable, Duplex A conductor con- 
sisting of two separate cables placed parallel 
to each other. 

The duplex cable is used especially in the al- 
ternating current system. 

CaMe, Electric The combination 

of an extended length of a single insulated 
conductor, or two or more separately insu- 
lated electric conductors, covered externally 
with a metallic sheathing or armor. 

Strictly speaking, the word cable should be 
limited to the case of more than a single con- 
ductor. Usage, however, sanctions the employ- 
ment of the word to indicate a single insulated 
conductor. 

The conducting wire may consist of a single 
wire, of a number of separate wires electrically 
connected, or of a number of separate wires in- 
sulated from one another. 

An electric cable consists of the following parts, 
viz.: 

(i.) The conducting wire or core. 

(2.) The insulating material for separating the 
several wires ; and 

(3.) The armor or protecting covering, consist- 
ing of strands of iron wire, or of a metallic coat- 
ing or covering of lead. 

As to their position, cables are aerial, sub- 
marine, or underground. As to their purpose, 



they are telegraphic, telephonic, or electric light 
and power cables. As to the number of their 
conductors they are single-wire or bunched 
cables. Bunched cables are straightaway or 
twisted. 

Fig. 94 shows a form of submarine cable the 




Fig. Q4. Electric Cable. 

armor of which is formed of strands of iron; 
wire. 

Cable, Electric Light or Power 

A cable designed to distribute the electric cur- 
rent employed in electric light or power sys- 
tems. 

Electric light cables are generally underground. 
They may be submarine. (See Cable, Electric.) 

Cable, Flat A cable, the separate 

conductors of which are laid-up side by side 
so as to form a flat conductor. 

A flat cable is suitable for house work as being: 
less objectionable in appearance when placed on 
the outside of ceilings or walls. 

Cable, Flat Duplex A flat, laid-up, 

cable containing two wires. 

Cable-Grip.— (See Grip, Cable) 

Cable-Hanger. — (See Hanger, Cable) 

Cable-Hanger Tongs. — (See Tongs, Cable- 
Hanger) 

Cable Laid-Up in Layers. — A term applied 
to a cable, all the conducting wires of which/ 
are in layers. 



Cab. 



69 



[Cab. 



Cable Laid-Up in Reversed Layers.— A 

term applied to a cable in which the conduct- 
ors, in alternate layers, are twisted in opposite 
directions. (See Cable, Bunched, Straight- 
away^) 

Cable Laid-Up in Twisted Pairs. — A term 
applied to a cable in which every pair of wires 
is twisted together. (See Cable, Bunched, 
Twisted?) 

Cable Lead.— (See Lead, Cable). 

Cable, Multiple-Core A cable con- 
taining more than a single core. 

Cable-Protector.— (See Protector, Cabled 

Cable-Serving". — (See Serving, Cabled) 

Cable, Single-Wire A cable con- 
taining a single wire or conductor 

Cable, Sub-Aqueous An electric 

cable designed for use under water. 

The term submarine is more frequently em- 
ployed. 

Cable, Submarine A cable designed 

for use under water. 

Submarine cables are either shallow-water, or 
deep-sea cables. Gutta-percha answers admirably 
for the insulating material of the core. Various 
other insulators are also used. 

Strands of tarred hemp or jute, known as the 
cable- serving, are wrapped around the insulated 
core in order to protect it from the pressure of the 
galvanized iron wire armor afterwards put on. 
To prevent corrosion the iron wire is covered 
with tarred hemp, galvanized, or otherwise 
coated. 

Submarine cables are generally employed for 
telegraphic or telephonic communication. (See 
Cable,- Electric.') 

Cable, Submarine, Deep-Sea — A 

submarine cable designed for use in deep 
water. 

This form of cable is not so heavily armored as 
the shallow-water submarine cable. 

Cable, Submarine. Shallow- Water . 

A submarine cable designed for use in shallow 
water. 

This cable is provided with a heavier armor or 
sheathing than a deep-sea cable to protect it 
from chafing due to the action of the waves and 
tides in shallow water. (See Cable, Submarine.) 



Cable Support, Underground (See 

Support, Underground Cable?) 

Cable Tank.— (See Tank, Cable.) 

Cable, Telegraphic A cable de- 
signed to establish telegraphic communication 
between different points. 

Telegraphic cables may be aerial, submarine^ 
or underground. (See Cable, Electric.) 

Cable, Telephonic A cable de- 
signed to establish telephonic communication 
between different points. 

Telephonic cables may be aerial, submarine, 
or underground. (See Cable. Electric. ) 

Cable-Terminal. — (See Terminal, Cable.\ 

Cable, Torpedo A cable, in the 

circuit of which a torpedo is placed. (See 
Torpedo, Electric?) 

Cable, Twisted-Pair A cable 

containing a single twisted pair, suitable for 
use as a lead and return, thus affording a 
metallic circuit. 

Cable, Two, Three, Four, etc., Conductor 

A cable containing two, three, four, 

or more separate conducting wires. 

Cable, Underground An electric 

cable placed underground. 

The conducting wires of an underground cable 
are surrounded by a good insulating, water-proof 
substance, and protected by a sheathing or armor. 
A coating of lead is very generally employed for 
the sheathing or armor. Underground cables, in 
order to be readily accessible, should be placed 
in an underground conduit or subway. (See 
Cable, Electric Conduit, Underground Electric. 
Stibway, Electric.) 

Cable^ Worming.— (See Worming, Cable.) 

Cablegram. — A message received by means 
of a submarine telegraphic cable. 

Cables, Laying-Up The placing or 

disposing of the separate cables or conduc- 
tors in a bunched cable. 

The separate conductors in cables may be Iaid- 
up "straightaway " or "twisted.'' (See Cable, 
Bunched, Twisted. Cable, Bunched, Straight- 
away. ) 

Cabling. — Sending a telegraphic dispatch. 
bv means of a cable. 



CaL] 



70 



[Cal. 



Calahan's Stock Printer. — (See Printer, 
Stock, Calahan's.) 

Calamine, Electric A crystalline 

variety of silicate of zinc that possesses pyro- 
electric properties. (See Electricity, Pyro) 

Cal-Electricity. — (See Electricity, Cal) 

Calibrate. — To determine the absolute 
or relative value of the scale divisions, or of 
the indications of any electrical instrument, 
such as a galvanometer, electrometer, vol- 
tameter, wattmeter, etc. 

Calibrating". — The act of determining the 
absolute or relative value of the deflections, 
or indications of an electric instrument. 

Calibration, Absolute The deter- 
mination of the absolute values of the read- 
ing of an electrometer, galvanometer, volt- 
meter, amperemeter, or other similar instru- 
ment. 

The calibration of a galvanometer, for ex- 
ample, consists in the determinatior of the law 
which governs its different deflections, and by 
which is obtained in amperes, either the absolute 
or the relative currents required to produce such 
deflections. 

For various methods of calibration, see stan- 
dard works on electrical testing, or on elec- 
tricity. 

Calibration, Invariable, of Galvanom- 
eter In galvanometers with absolute 

calibration, a method for preventing the oc- 
currence of variations in the intensity of the 
field of the galvanometer, due to the neigh- 
borhood of masses of iron, etc. 

Calibration, Relative The deter- 
mination of the relative values of the reading 
of an electrometer, voltmeter, amperemeter, 
or other similar instrument. 

Caliper, Mi- 
crometer 



— A name some- 
times given to a 
vernier wire 
gauge. (See 
Gauge, Vernier 

Wire) Fig. 95. Micrometer Caliper. 

A form of micrometer caliper is shown in Fig. qq. 




Call-Bell, Extension (See Bell, 

Extension Call) 
Call-Bell, Magneto-Electric An 

electric call-bell operated by currents pro- 
duced by the motion of a coil of wire before 
the poles of a permanent magnet. 

A well known form of magneto call-bell is shown 




Fig. q6. Magneto Call Bell. 

in Fig. 96. The armature is driven by the rota- 
tion of the handle 

Call-Bell, Telephone An electric 

bell, the ringing of which is used to call a 
person to a telephone. 

Call, Electric Bell — An electric 

bell sometimes used to call the attention of an 
operator to the fact that his correspondent 
wishes to communicate with him, or to notify 
an attendant that some service is desired. 

Call, Messenger — A district call- 
box. (See Box, District Call) 

Call, Thermo-Electric An instru- 
ment for sounding an alarm when the tem- 
perature rises above, or falls below, a fixed 
point. 

In one form of thermo-electric call a needle is 
moved over a dial by a simple thermic device and 
rings a bell when the temperature for which it 
has been se is attained. The thermo-call is appli- 
cable to the regulation of the temperature oi 



Cal.] 



71 



[Cal. 



dwellings, incubators, hot houses, breweries, dry- 
ing rooms, etc. 

Callaud Voltaic Cell.— (See Celt, Vol- 
taic, Callaud's.) 

Calling-Drop. — (See Drop, Calling) 

Calorescence. — The transformation of 
invisible heat-rays into luminous rays, when 
received by certain solid substances. 

The term was proposed by Tyndall. The light 
from a voltaic arc is passed through a hollow 
glass lens rilled with a solution of iodine in bisul- 
phide of carbon. 

This solution is opaque to light but quite trans- 
parent to heat. 

If a piece of charred paper, or thin platinum 
foil, is placed in the focus of these invisible rays, 
it will be heated to brilliant incandescence, (See 
Focus.) 

Calorie. — A term formerly applied to the 
fluid which was believed to be the cause or 
essence of heat. 

The use of the word caloric at the present time 
is very unscientific, since heat is now known to 
be an effect of a wave motion and not a material 
thing. (See Heat ) 

Calorie. — A heat unit. 

There are two calories, the small and the large 
calorie. 

The amount of heat required to raise the tem- 
perature of one gramme of water from o degree 
C. to i degree C. is called the small calorie. 

The amount of heat required to raise 1,000 
grammes, or a kilogramme, of water from o de- 
gree C. to i degree C. is called the great calorie. 
The first usage of the word is the commoner. 

This word is sometimes spelled calory. 

Calorie, Great — The amount of 

heat required to raise the temperature of one 
kilogramme of water from o degree C. to I 
degree C. 

Calorie, Small — The amount of 

heat required to raise the temperature of one 
gramme of water from o degree C. to i 
degree C. 

Calorimeter — An instrument for measur- 
ing the amount of heat or thermal energy 
contained or developed in a given body. 

Thermometers measure temperature only. A 



thermometer plunged in a cup full of boiling 
water shows the same temperature that it would 
in a tub full of boiling water. The quantity of 
heat energy present in the two cases is of course 
greatly different, and can be measured by a cal- 
orimeter only. 

Various forms of calorimeters are employed. 

In order to determine the quantity of heat in 
a given weight of any body, this weight may be 
heated to a definite temperature, such as the boil- 
ing point of water, and placed in a vessel con- 
taining ice. The quantity of ice melted by the 
body in cooling to the temperature of the ice, is 
determined by measuring the amount of water 
derived from the melting of the ice. Care must 
be observed to avoid the melting of the ice by ex- 
ternal heat. 

In this way the amount of heat required to 
raise the temperature of a given weight of a body 
a certain number of degrees, or the capacity of 
the body for heat, may be compared with the 
capacity of an equal weight of water. This ratio 
is called the specific heat. (See Heat, Specific.) 

The heat energy, present in a given weight of 
any substance at a given temperature, can be de- 
termined by means of a calorimeter; for, since a 
pound of water heated i° F. absorbs an amount 
of energy equal to 772 foot-pounds, the energy can 
be readily calculated if the number of pounds of 
water and the number of degrees of temperature 
are known. (See Heat, Mechanical Equivalent 
of-) 

Calorimeter, Electric An instru- 
ment for measuring the heat developed in a 
conductor or any piece of electrical apparatus, 
in a given time, by an electric current. 




Fig. 97. Electric Calorimeter. 

A vessel containing water is provided with a 
thermometer T, Fig. 97. The electric current 



Cal.] 



72 



[Can. 



passes for a measured time through, a wire im- 
mersed in the liquid. 

The quantity of heat is determined from the 
increase of temperature, and the weight of the 
water heated. 

According to Joule, the number of heat units 
developed in a conductor by an electric current 
is proportional: 

(i.) To the resistance of the conductor. 

(2.) To the square of the current passing. 

(3.) To the time the current is passing. 

(See Heat Unit, English.) 

The heating power of a current is as the square 
of the current only when the resistance remains 
the same. (See Heat, Electric.) 

Calorimetric. — Pertaining to or by means 
of the calorimeter. 

Calorimetric measurement is the measurement 
of heat energy made by means of the calorimeter. 
(See Calorimeter.) 

Calorimetrically. — In a calorimetric man- 
ner. 

Calorimetric Photometer. — (See Photom- 
eter, Calorimetric?) 

Calorimotor. — A name applied to a defla- 
grator. (See Deflagrator? 

Calory. — A term used for calorie. 

Calorie is the preferable orthography. (See 
Calorie. ) 

Cam, Electro-Magnetic —A form 

of magnetic equalizer, which depends for its 
operation on the lateral approach of a suita- 
bly shaped polar surface. (See Equalizer* 
Magnetic?) 

Cam, Listening In a telephone 

exchange system, a metallic cam by means of 
which an operator is placed in circuit with 
a subscriber. 

Candle. — The unit of photometric intensity. 

Such a light as would be produced by the 
consumption of two grains of a standard 
candle per minute. 

An electric lamp of 16 candle-power, or one of 
2,000 candle-power, is a light that gives respect- 
ively 16 or 2,000 times as much light as one stand- 
ard candle. 

Candle Burner, Electric (See Bur- 
ner, Electric Candle?) 



Candle, Electric A term applied 

to the Jablochkoff candle, and other similai 
devices. (See Candle, Jablochkoff,) 

Candle, Foot A unit of illumina- 
tion equal to the illumination produced by a 
standard candle at the distance of 1 foot. 

According to this unit, the illumination pro- 
duced by a standard candle at the distance of 
2 feet would be but the one -fourth of a foot- 
candle; at 3 feet, the one-ninth of a foot-candle, 
etc. 

The advantageof the proposed standard lies in- 
the fact that knowing the illumination in foot- 
candles required for the particular work to be 
done, it is easy to calculate the position and 
intensity of the lights required to produce the 
illumination. 

Candle, Jablochkoff An electric 

arc light in which the two carbon electrodes are 
placed parallel to each other and maintained 
a constant distance apart by means of a sheet 
of insulating material placed between them. 

The Jablochkoff electric candle consists of two 
parallel carbons, separated by a layer of kaolin or 
other heat-resisting insulating material, as shown 
in Fig. 98. The current is passed into and out of 
the carbons at one end of the 
candle, and forms a voltaic arc at 
the other end. In order to start 
the arc, a thin strip called the 
igniter, consisting of a mixture of 
some readily ignitable substance, 
connects the upper ends of the 
carbons. 

An alternating current is em- 
ployed with these candles, thus 

avoiding the difficulty which Fi s> 9 8 Ja ' 

u ,v r ,1 blochkoff Candle* 

would otherwise occur from the M 

more rapid consumption of the positive than the 

negative carbon. (See Current, Alternating.) 

Candle, Metre The illumination pro- 
duced by a standard candle at the distance of 
one metre. (See Candle, Foot?) 

Candle-Power.— (See Power, Candle?) 

Candle-Power, Rated (See Power, 

Candle, Rated?) 

Candle ■ Power, Spherical (See 

Power, Candle, Spherical?) 

Candle, Standard - 




— A candle of 



Cao.] 



73 



[Cap. 



definite composition which, with a given con- 
sumption in a given time, will produce a light 
of a fixed and definite brightness. 

A candle which burns 120 grains of sperma- 
ceti wax per hour, or 2 grains per minute, will 
give an illumination equal to one standard candle. 
Unless considerable care is taken, erroneous re- 
suits will be obtained from the use of the stand- 
ard candle. According to Shngo and Brooker 
the following are among the most important 
causes of these errors : 

(1.) Defective forms of candle which cause a 
varying consumption of the material per second, 
and consequently a varying light for the standard 
candle. 

(2.) Variations in the composition of the sper- 
maceti of which the candle is composed. Sper- 
maceti is not a definite chemical compound, but 
consists of a mixture of various substances ; 
therefore, even if the consumption is maintained 
constant, the light-giving power is not necessarily 
constant. 

(3.) Variations in the composition and charac 
ter of the wick, such as the number and size of 
the threads of which it is formed and the closeness 
of the strands, all of which circumstances influence 
the amount of light given off by the candle. 

(4.) The light emitted in certain directions va- 
ries in a marked degree with the shape of the 
wick. The mere bending of a wick may, there- 
fore, cause the amount of light to vary consider- 
ably. 

(5.) The light varies with the thickness of the 
wick. Thick wicks give less light than thin 
wicks. 

(6.) The light given by the standard candle va- 
ries with the temperature of the testing-room. 
As the temperature rises the light given by the 
standard candle increases. 

(7.) Currents of air. by producing variations 
in the amount of melting wax in the cup of the 
candle, vary the amount of light emitted. 

These difficulties in obtaining a fixed amount of 
light from a standard candle, together with the 
difficulty of comparing the feeble light of a single 
candle with the light of a much more powerful 
source, such as an arc lamp, coupled with the 
additional difficulty arising from the difference in 
the colors of the lights, have led to the use of 
other standards of light than those furnished by 
the standard candle. 

Caontckouc. or India-Rubber.— A resin- 



ous substance obtained from the milky juices 
of certain tropical trees. 

Caoutchouc possesses high powers of electric 
insulation, and is used either pure or combined 
with sulphur. 

Cap, Insulator A covering or cap 

placed some distance above an insulator, but 
separated from it by an air space.' 

Insulator caps are intended for protection of the 
insulators from injury by the throwing of stones 
or other malicious acts. Insulator caps are gen- 
erally made of iron. They are highly objection- 
able, owing to the facility they offer for the ac- 
cumulation of dust and dirt. 

Capacity, Atomic The quantiva- 

lence or valency of an atom. (See Atomi- 
city^) 

Capacity, Dielectric A term em- 
ployed in the same sense as specific inductive 
capacity. (See Capacity, Specific Inductive!) 

Capacity, Electro-Dynamic — A 

term formerly employed by Sir William 
Thomson for self-induction. (See Induction, 
Self) 

Capacity, Electrostatic The quan- 
tity of electricity which must be imparted to a 
given body or conductor as a charge, in order 
to raise its potential a certain amount. (See 
Potential, Electric) 

The electrostatic capacity of a conductor is not 
unlike the capacity of a vessel filled with a liquid 
or gas. A certain quantity of liquid will fill a 
given vessel to a level dependent on the size or 
capacity of the vessel. In the same manner a 
given quantity of electricity will produce, in a 
conductor or condenser, a certain difference of 
electric level, or difference of potential, dependent 
on the electrical capacity of the conductor or 
condenser. 

Or, taking the analogous case of a gas-tight 
vessel, the quantity of gas that can be forced into 
such a vesssl depends on the size of the vessel 
and the pressure with which it is forced in. A 
tension or pressure is thus produced by the gas 
on the walls of the vessel, which is greater the 
smaller the size of the vessel and the greater the 
quantity of gas forced in. 

In the same manner, the smaller the capacity 
of a conductor, the smaller is the charge required 



Cap.] 



74 



[Cap. 



to raise it to a given potential, or the higher the 
potential a given charge will raise it. 

The capacity K, of a conductor or condenser, 
is therefore directly proportional to the charge Q, 
and inversely proportional to the potential V; or, 

Q 

K = — . 

V 

From which we obtain Q = KV ; or, 

The quantity of electricity required to charge a 
conductor or condenser to a given potential is 
equal to the capacity of the conductor or condenser 
multiplied by the potential through which it is 
raised. 

Capacity, Electrostatic, Unit of 

Such a capacity of a conductor or condenser 
that an electromotive force of one volt will 
charge it with a quantity of electricity equal 
to one coulomb. 

The farad. (See Farad.) 

Capacity of Cable. — (See Cable, Capacity 
of) 

Capacity of Condenser. — (See Condenser, 
Capacity of.) 

Capacity of Leyden Jar. — (See Jar, 
Leyden, Capacity of.) 

Capacity of Line. — (See Line, Capacity 
of) 

Capacity of Polarization of a Yoltaic 
Cell. — (See Cell, Voltaic, Capacity of Polar- 
ization of.) 

Capacity, Safe Carrying, of a Conductor 

— The maximum electric current the 

conductor will carry without becoming unduly 
heated. 

Capacity, Specific Inductive 

The ability of a dielectric to permit induction 
to take place through its mass, as compared 
with the ability possessed by a mass of air of 
the same dimensions and thickness, under 
precisely similar conditions. 

The relative power of bodies for trans- 
mitting electrostatic stresses and strains 
analogous to permeability in metals. 

The ratio of the capacity of a condenser 
whose coatings are separated by a dielectric 
of a given substance to the capacity of a 
similar condenser whose plates are separated 
by a plate or layer of air. 



The inductive capacity of a dielectric is com- 
pared with that of air. 

According to Gordon and others, the specific 
inductive capacities of a few substances, com- 
pared with air, are as follows: 

Air i.oo 

Glass 3-OI3 to 3.258 

Shellac 2.740 

Sulphur 2.580 

Gutta-percha 2.462 

Ebonite 2.284 

India-rubber 2.220 to 2.497 

Turpentine 2.160 

Petroleum 2.030 to 2.070 

Paraffin (solid) 1-994 

Carbon bisulphide 1.810 

Carbonic acid 1. 00036 

Hydrogen 0.99967 

Vacuum 0.99941 

Faraday, who proposed the term specific in- 
ductive capacity, employed in his experiments a 
condenser consisting of a metallic sphere A, Fig. 
99, placed inside a large 
hollow sphere B. 

The concentric space 
between A and B was filled 
with the substance whose 
specific inductive capacity 
was to be determined. 

Capacity, Specific 

Magnetic A term 

sometimes employed in 
the sense of magnetic 
permeability. 

Conductibility for lines 
of magnetic force in the 
same sense that specific 
inductive capacity is con- 
ductibility for lines of 
electrostatic force. 

This term has received 
the name of specific mag- 
netic capacity in order to distinguish it from specific 
inductive capacity. The velocity of propagation 
of waves in any elastic medium is proportional to 
the quotient obtained by extracting the square 
root of the elasticity of the medium divided by 
the square root of its density ; or, 




Fig 99. Condenser. 



V 



\D* 



Cap/ 



75 



[Car, 



Similarly, the speed with which inductive waves 
travel depends on the relation between the elas- 
ticity and the density of the medium. Calling == 

the electric elasticity, then its reciprocal, K, corre- 
sponds with the dielectric capacity. The elec- 
trical density, //, corresponds with the magnetic 
permeability. The velocity of wave transmission 
is therefore, 



\J 



~ vkxm' 



Capacity, Storage, of Secondary Cell 

— (See Cell, Secondary or Storage, Capa- 
city of.) 

Capillarity. — The elevation or depression 
of liquids in tubes of small internal diameter. 

The liquid is elevated when it wets the walls, 
and depressed when it does not wet the walls of 
the tube. 

The phenomena of capillarity are due to the 
mutual attractions existing between the mole- 
cules of the liquid for one another, and the 
mutual attraction between the molecules of the 
liquid and those of the walls of the tube. 

In capillarity, therefore, the approximately 
level surface caused by the equal attraction of all 
the molecules towards the earth's centre is dis- 
turbed by the unequal attraction exerted on each 
molecule by the walls of the tube and by the re- 
maining molecules. 

Capillarity, Effects of, on Toltaic Cell 

Effects caused by capillary action 

which disturb the proper action of a voltaic 
cell. 

These effects are as follows: 

(i.) Creeping, or efflorescence of salts. (See 
Creeping, Electric. Efflorescence. ) 

(2.) Oxidation of contacts and consequent in- 
troduction ot increased resistance into the battery 
circuit. The liquid enters the capillary spaces 
between the contact surfaces and oxidizes them. 

Capillary. — Of a small or hair-like diame- 
ter or size. 

A capillary tube is a tube of small hair-like di- 
ameter. (See Capillarity .) 

Capillary Attraction. — (See Attraction, 
Capillary?) 



Capillary Contact-Key.— (See Key, Cap- 
illary Contact^) 

Capillary Electrometer.— (See Electrom- 
eter, Capillary.) 

Carbon. — An elementary substance which 
occurs naturally in three distinct allotropic 
forms, viz.: charcoal, graphite and the dia- 
mond. (See Allotropy.) 

Carbon-Brushes for Electric Motors. — 

(See Brushes, Carbon, for Electric Motors?) 

Carbon Button. — (See Button, Carbon.) 
Carbon-Clutch or Clamp of Arc Lamp. 

— (See Clutch, Carbon, of Arc Lamp?) 

Carbon-Electrodes for Arc Lamps. — (See 
Electrodes, Carbon, for Arc Lamps.) 

Carbon-Holders for Arc Lamps. — (See 
Holders, Carbon, for Arc Lamps?) 

Carbon Points. — (See Points, Carbon.) 

Carbon Transmitter for Telephones. — 
(See Transmitter, Carbon, for Telephones?) 

Carbonic Acid Gas. — (See Gas, Carbonic 
Acid?) 

Carboning- Lamps. — (See Lamps, Carbon- 
ing.) 

Carbonizable. — Capable of being carbon- 
ized. (See Carbonization, Processes of.) 

Carbonization. — The act of carbonizing, 
(See Carbonization, Processes of.) 

Carbonization, Processes of 

Means for carbonizing material. 

The carbonizable material is placed in suitably 
shaped boxes, covered with powdered plumbago 
or lampblack, and subjected to the - prolonged 
action of intense heat while out of contact with 
air. 

The electrical conducting power of the carbon 
which results from this process is increased by the 
action ot the heat, and, probably, also, by the de- 
posit in the mass, ot carbon resulting from the 
subsequent decomposition of the hydro-carbon 
gases produced during carbonization. 

When the carbonization is for the purpose of 
producing conductors for incandescent lamps, in 
order to obtain the unifo-mity of conducting 
power, electrical homogeneity, purity and high 
refractory power requisite, selected fibrous ma- 
terial, cut or shaped in at least one dimension 



€ar.J 



'6 



[Car. 



prior to carbonization, must be taken, and sub- 
jected to as nearly uniform carbonization as pos- 
sible. 

Carbonize. — To reduce a carbonizable ma- 
terial to carbon. (See Carbonization, Pro- 
cesses of) 

Carbonized Cloth Discs for High Resist- 
ances. — (See Cloth Discs Carbonized, for 
High Resistances) 

Carbonizer. — Any apparatus suitable for 
reducing carbonizable material to carbon. 

Carbonizing. — Subjecting a carbonizable 
substance to the process of caibonization. 
(See Carbonization, Processes of) 

Carbons, Artificial —Carbons ob- 
tained by the carbonization of a mixture of 
pulverized carbon with different carbonizable 
liquids. 

Powdered coke, or gas-retort carbon, some- 
times mixed with lamp-black or charcoal, is made 
into a stiff dough with molasses, tar, or any other 
hydro-carbon liquid. The mixture is molded 
into rods, pencils, plates, bars or other desired 
shapes by the pressure of a powerful hydraulic 
press. After drying, the carbons are placed in 
crucibles and covered with lamp-black or pow- 
dered plumbago, and raised to an intense heat at 
which they are maintained for several hours. By 
the carbonization of the hydro-carbon liquids, the 
carbon paste becomes strongly coherent, and by 
the action of the heat its conducting power in- 
creases. 

To give increased density after baking, the 
carbons are sometimes soaked in a hydro-carbon 
liquid, and subjected to a re-baking. This may 
be repeated a number of times. 

Carbons, Concentric-Cylindrical 

A cylindrical rod of carbon placed inside a hol- 
low cylinder of carbon but separated from it 
by an air space, or by some other insulating^ 
refractory material. 

Jablochkoff candles sometimes are made with a 
solid cylindrical electrode, concentrically placed 
in a hollow cylindrical carbon. 

Carbons, Cored A cylindrical carbon 

electrode for an arc lamp that is molded 
around a central core of charcoal, or other 
softer carbon. 



Much of the unsteadiness of the arc light is due 
to changes in the position of the arc. Cored car- 
bons, it is claimed, render the arc light steadier, 
by maintaining the arc always at the softer carbon 
and hence at the central point of the electrode. 

A core of harder carbon, or other refractory 
material, is sometimes provided for the negative 
carbon. 

Carbons, Flashed Carbons which 

have been subjected to the flashing pro- 
cess, (See Carbons, Flashing Process for) 

Carbons, Flashing" Process for A 

process for improving the electrical uniformity 
of the carbon conductors employed in in- 
candescent lighting, by the deposition of car- 
bon in their pores, and over their surfaces at 
those places where the electric resistance is 
relatively great. 

The carbon conductor or filament is placed in 
a vessel filled with the vapor of a hydrocarbon 
liquid called rhigolene, or any other readily de- 
composable hydrocarbon liquid, and gradually 
raised to electric incandescence by the passage 
through it of an electric current. A decomposi- 
tion of the hydrocarbon vapor occurs, the car- 
bon resulting therefrom being deposited in and on 
the conductor. 

As the current is gradually increased, the 
parts of the conductor first rendered incandes- 
cent are the places where the electric resist- 
ance is the highest, these parts, therefore, and 
practically these parts only, receive the deposit 
of carbon. As the current increases, other 
portions become successively incandescent and 
receive a deposit of carbon, until at last the 
filament glows with a uniform brilliancy, in- 
dicative of its electric homogeneity. 

A carbon whose resistance varies considerably 
at different parts could not be successfully em- 
ployed in an incandescent lamp, since if heated 
by a current sufficiently great to render the points 
of comparatively small resistance satisfactorily 
incandescent, the temperature of the points of 
high resistance would be such as to lower the life 
of the lamp, while if only those portions were 
safely heated, the lamp would not be economical. 
The flashing process is therefore of very great 
value in the manufacture of an incandescent 
lamp. 

The name " flashing " was applied to the pro- 
cess by reason of the flashing light emitted by the 



Car.] 



[Cas. 



carbons when they have been sufficiently treated. 
The process requires so little time that the dull red 
which first appeari soon flashes to the full lumin- 
osity required. 

The term "flashing" is sometimes applied to 
the electrical heating to incandescence, while the 
carbons are in the lamp chambers, and on the 
pumps. This flashing is for the purpose of 
driving off all the gases occluded by the carbon, 
so that these gases may be carried off by the 
operation of pumping. This process is more 
properly called the process for driving off the 
-occluded gases. 

The carbons are sometimes flashed in the liquid 
itself instead of in its vapor. 

Carbons, Paper Carbons, of textile 

or fibrous origin, obtained from the carboniza- 
tion of paper. 

The carbonization of paper is readily effected 
by submitting the paper to the prolonged action 
of a high temperature while out of contact with 
air. 

For this purpose the paper is packed in retorts 
or crucibles, and covered with lamp-black, or 
powdered plumbago, in order to exclude the air. 

Since paper consists of a plane of material uni- 
formly thin in one direction, formed almost en- 
tirely of fibres of pure cellulose, the greatest 
length of wh.'ch extends in a direction nearly par- 
allel to that in which the paper is uniformly thin, 
it is clear that sheets of this substance, when car- 
bonized, should yield flexible carbons of unusual 
purity and electrical homogeneity, since such 
carbons are structural in character, and are uni- 
formly affected by the heat of carbonization to an 
extent that would be impossible by the carboniza- 
tion of any material in a mass. 

Carcase of Dynamo-Electric Machine. — 

(See Machine, Dynamo-Electric , Carcase of.) 
Carcel.— The French unit of light. The 
light emitted by a lamp burning 42 grammes 
of pure colza oil per hour, with a flame 40 
millimetre? in height. 

The bec-carcel. One carcel == 9.5 to 9.6 stand- 
ard candles. 

Carcel Lamp. — (See Lamp, Carcel) 
Carcel Standard Gas Jet. — (See Jet, Gas, 

Carcel Standard) 
Card, Compass A card used in the 

mariner's compass, on which are marked the 



four cardinal points of the compass N, S, E 
and W, and these again divided into thirty- 
two points called Rhumbs. (See Compass, 
Azwiuth) 

Cardew Voltmeter. — (See Volt?neter, 
Car dew.) 

Carriage, Pen The carriage in an 

electric chronograph which holds the pen and 
moves over the sheet of paper on which the 
record is made. (See Chronograph, Elec- 
tric.) 

Carriers of Replenishes — (See Replen- 
isher, Carriers of.) 
Cascade, Charging" Leyden Jars by 

— A method of charging jars or condensers 
by means of the free electricity liberated by 
induction from one coating, when a charge is 
passed into the other coating. 

The jars are p'acei as shown m Fig. 100, with 
the inside coating of the first jar connected with 
the outside coaang of the one next it. There is in 
Jt Q 




Fig. 100. Cascade Charging- of Leyden Jars. 

reality no increase in the entire charge obtained 
in charging by cascade, since the sum of the 
charges given to the separate jars is equal to 
the same charge given to a single jar separately 
charged. 

The energy of the discharge in cascade can be 
shown to be less than that of the same charge 
when confined to a single jar. This is of course 
to be expected, since it is energy that is charged 
in the jar and not electricity, and, of course, the 
energy charged in the jar can never exceed the 
energy employed in charging the jar. There is 
a small loss for each jar, and this increases ne- 
cessarily with each jar added. 

Cascade, Connection of Electric Sonrces 

in A term sometimes used for series- 
connection of electric sources. 

The term series -connection is the preferable 
one. (See Connection, Series.) 

Case-Hardening, Electric Super- 
ficially converting a piece of wire into steel 
by electrically produced heat. 



Cas.] 



78 



[Cau. 



In electric case-hardening, the superficial layers 
of a piece of iron are converted into steel by 
electrically heating the same, while surrounded 
by a layer of case-hardening flux and carbonaceous 
substances such as animal charcoal, shavings "of 
horn, leather cuttings or other similar substances. 

In the case of a readily oxidizable metal like 
iron, oxidation is prevented by surrounding the 
metal by a hydrocarbon gas, which, when suffi- 
ciently heated, deposits on the surfaces a pro- 
tective coating of carbon. This layer of carbon 
gradually carbonizes the iron. 

Case Wiring. — (See Wiring, Case.) 

Cataphoresis.— A term sometimes em- 
ployed in place of electric osmose. (See Os- 
mose, Electric!) 

The word cataphoresis applies to the cases where 
medicinal substances, such as iodine, cocoaine, 
quinine, etc., are caused to pass through organic 
tissues in the direction of flow of an electric cur- 
rent, or from the anode to the kathode. This 
action is probably due to an electrolytic action. 

Cataphoric Action. — (See Action, Cata- 
phoric.) 

Catch, Safety A wire, plate, strip, 

or box of readily fusible metal, capable of con- 
ducting, without fusing, the current ordinarily 
employed on the circuit, but which fuses and 
thus breaks the circuit on the passage of an 
abnormally large current. 

Safety-catches are generally placed on multiple- 
arc and multiple -series circuits. (See Fuse, 
Safety.) 

Catelectro tonus,— An orthography some- 
times applied to Kathelectrotonus. (See 
Katkelectrotonus) 

Cathetometer. — An instrument for the ac- 
curate measurement of vertical height. 

The cathetometer consists essentially of an 
accurately divided vertical rod which carries a 
sliding support for a telescope. The telescope is 
provided with two spider lines at right angles to 
one another, so placed as to be seen in front of 
the object whose height is to be measured. From 
observations taken in different positions, the 
measurement of the true vertical height is readily 
obtained. 

Cathion. — A term sometimes used instead 
of Kathion. 



More correctly written Kathion. (See 
Kathion.) 

Cathode. — A term sometimes used instead 
of Kathode. 

Catoptrics. — That branch of optics which 
treats of the reflection of light. 

Causty, Galvano A term some- 
times used for galvano-cautery. (See Cautery, 
Galvano.) 

Cauterization. — The act of cauterizing, or 
burning with a heated solid or caustic sub- 
stance. 

Cauterization, Electric Subject- 
ing to cauterization by means of a wire elec- 
trically heated. (See Cautery, Electric) 

Cauterize. — To subject to cauterization, or 
burning with a heated solid or caustic sub- 
stance. 

Cauterizer, Electric A term some- 
times applied to an electric cautery. (See' 
Cautery, Electric) 

Cautery, Actual A burning or sear- 
ing with a white-hot metal. 

Cautery Battery. — (See Battery, Cautery.} 

Cautery, Electric An instrument 

used for electric cauterization. 

In electro-therapeutics, the application of 
variously shaped platinum wires heated to in- 
candescence by the electric current in place 
of a knife, for removing diseased growths, or 
for stopping hemorrhages. 

The operation, though painful during applica- 
tion, is afterward less painful than that with a 
knife, since secondary hemorrhage seldom occurs^, 
and the wound rapidly heals. 

Electric cautery is applicable in cases where 
the knife would be inadmissible owing to the 
situation of the parts or their surroundings. 

Cautery, Galvano — A term fre- 
quently employed in place of electric cautery. 
(See Cautery, Electric) 

Cautery, Galyano Electric — Art 

electric cautery. (See Cautery, Electric) 

Cautery, Galvano Thermal —A 

term sometimes used for an electric cautery „> 
(See Cautery, Electric^ 



Cau.J 



79 



[Cel, 



Cautery-Knife Electrode.— (See Electrode, 
Ca utery-Knife.) 

Cautery, Thermal — A cautery 

heated by heat other than that of electric ori- 
gin, as distinguished from an electric cautery. 
(See Cautery, Electric?) 

Ceiling Rose.^-(See Rose, Ceiling.) 

Cell, Depositing" — An electrolytic 

cell in which an electro-metallurgical deposit is 
made, (See Metallurgy. Electro.) 

Cell, Electrolytic A cell or vessel 

containing an electrolyte, in which electrolysis 
is carried on. 

An electrolytic cell is called a voltameter when 
the value of the current passing is deduced from 
the weight of the metal deposited. 

Cell, Impulsion A photo-electric 

cell whose sensitiveness to light may be re- 
stored or destroyed by slight impulses given 
to the plates, such as by blows or taps, or elec- 
tro-magnetic impulses. 

An impulsion cell may be prepared by pasting 
pieces of tin-foil, the opposite faces of which are 
respectively polished and dull, on the opposite 
faces of a plate of glass, so as to expose dissimi- 
lar sides to the light, when the cells are dipped 
in alcohol. 

Cell, Photo-Electric A cell capa- 

ble of producing differences of potential 
when its opposite faces are unequally exposed 
to radiant energy. 

Photo-voltaic cells are made in a variety of 
forms, both with selenium and with different me- 
tallic substances. (See Cell, Selenium. ) 

Cell, Porous — A jar of unglazed 

earthenware, employed in double-fluid voltaic 
cells, to keep the two liquids separated. 

The use of a porous cell necessarily increases 
the internal resistance of the cell, from the de- 
crease it produces in the area of cross section of 
liquid between the two elements. When the bat- 
tery is dismantled, the porous cells should be 
kept under water, otherwise the crystallization of 
the zinc sulphate or other salt is apt to produce 
serious exfoliation, or scaling off, or even to 
crumble the porous cell. 

A porous cell is sometimes called a diaphragm, 
but only properly so when the cell is reduced to 
a single separating plate. (See Cell, Voltaic.) 



-A term sometimes 



Cell, Secondary — 

used instead of storage cell. 

The term secondary cell is used in contradis- 
tinction to primary or voltaic cell. 

Cell. Secondary or Storage. Boiling of 

A term sometimes applied to the 

gassing of a storage cell, (See Cell, Storage, 
Gassing of.) 

Cell, Secondary or Storage, Capacity of 

The product of the current in am- 
peres, by the number of hours the battery is 
capable of furnishing said current, when 
fully charged, until exhausted. 

The capacity of storage cells is given in ampere- 
hours. A storage battery with a capacity of 1,000 
ampere-hours can furnish, say a current of fifty 
amperes for twenty hours, or a current of one 
hundred amperes for ten hours; or a current of 
twenty-five amperes for forty hours. 

Cell, Secondary or Storage, Grassing of 

An escape of gas due to the decom- 
position of water on passage of too strong a 
charging current. 

Cell, Secondary or Storage, Renovation 

of The revivifying or recharging of a 

run-down, or discharged storage cell. 

Cell, Secondary or Storage, Time-Fall 

of Electromotive Force of — (See 

Force. Electromotive of Secondary or 
Storage Cell, Tiine-Fall, of.) 

Cell, Secondary or Storage, Time-Rise 

of Electromotive Force of (See 

Force, Electromotive of, Seco?idary or 
Storage Cell, Time-Rise, of.) 

Cell, Selenium A cell consisting 

of a mass of selenium fused in between two 
conducting wires or electrodes of platinized 
silver or other suitable metal. 

A convenient manner of forming a selenium 
cell is to wind two separate spirals of platinized 
silver wire around a cylinder of hard wood, tak- 
ing care to maintain them a constant distance 
apart, so as to avoid contact between them. The 
space between these wires is filled with fused sele- 
nium, which is allowed to cool gradually. 

Exposure to sunlight reduces the resistance of 
a selenium cell to about one-half its resistance in 



Cel.] 



80 



[Cel. 



the dark, but neither the resistance nor the reduc- 
tion ratio long remains constant. 

A selenium cell produces a difference of poten- 
tial, or electromotive force, when one of its elec- 
trode faces is exposed to light, while the other is 
kept in darkness. 

According to Von Uljanin, who experimented 
with selenium melted in between two parallel 
platinized plates, cooled under pressure, and then 
reduced from the amorphous to the sensitive crys- 
talline variety by gradual cooling alter two or 
three heatings in a paraffme bath up to 195 de- 
grees, the following peculiarities were observed: 

(1.) Exposure of one of the electrodes to sun- 
light produced an electromotive force which 
causes a current to flow from the dark to the 
illumined electrode. 

(2.) The maximum electromotive force was 
0.12 volt. 

(3.) The electromotive force disappeared instan- 
taneously and completely on the darkening of the 
electrodes. 

(4.) A slight difference in the electromotive 
force was observed when the positive and nega- 
tive electrodes were alternately exposed to the 
light, the maximum electromotive force being 
attained by the exposure of the negative electrode. 

(5.) If both electrodes are similarly illumined 
the resulting current strength is decreased and 
may reach zero. 

(6.) The action of light is instantaneous. 

(7.) Most of the selenium cells experimented 
with exhibited an electromotive force of polariza- 
tion. 

(8.) The electromotive force of polarization is 
diminished by exposure to light. 

(9.) The electrical resistance and sensitive- 
ness to light as regards the production of an 
electromotive force decrease with time. This 
is probably due to a gradual change in the allo- 
tropic state of the selenium. (See State, Allo- 
tropic. ) 

(10.) The electromotive force produced is pro- 
portional to the intensity of the illumination only 
when the obscure rays or heat rays are absent. 

(11.) Of different wave lengths the orange-yel- 
low rays in the diffraction spectrum, and the 
greenish-yellow in the prismatic ?pectrum pro- 
duced the greatest effect. 

Among some of the more recent applications 
of selenium cells are the following: 

(1.) A selenium cell is so placed in a circuit 
containing an electro-magnet and switch, that on 



one of its electrodes being exposed to the de- 
creased illumination of coming night it automat- 
ically turns on an electric lamp, and, conversely, 
on the approach of daylight, and the consequent 
illumination of the electrode, turns it off. 

(2.) A device whereby the presence of light, 
as for example that carried by a burglar, auto- 
matically rings an alarm and thus calls the atten- 
tion of the watchman of the building. 

Cell, Standard (See Cell, Voltaic, 

Standard^) 

Cell, Storage Two relatively inert 

plates of metal, or of metallic compounds, 
immersed in an electrolyte incapable of acting 
considerably on them until after an electric 
current has been passed through the liquid 
from one plate to the other and has changed 
their chemical relations. 

A single one of the cells required to form 
a secondary battery. 

Sometimes, the jar containing a single cell 
is called a storage cell. 

This latter use of the word is objectionable. 

A storage cell is also called an accumulator. 

On the passage of an electric current through 
the electrolyte, its decomposition is effected and 
the electro-positive and electro-negative radicals 
are deposited on the plates, or unite with them, 
so that on the cessation of the charging current, 
there remains a voltaic cell capable of generating 
an electric current. 

A storage cell is charged by the passage through 
the liquid from one plate to the other of an elec- 
tric current, derived from any external source. 
The charging current produces an electrolytic de- 
composition of the inert liquid between the 
plates, depositing the electro-positive radicals, or 
kathions, on the plate connected with the negative 
terminal of the source, and the electro -negative 
radicals, or anions, on the plate connected with 
the positive terminal. 

On the cessation of the charging current, and 
the connection of the charged plates by a con- 
ductor outside the liquid, a current is produced, 
which flows through the liquid from the plate 
covered with the electro-positive radicals, to that 
covered with the electro -negative radicals, or in 
the opposite direction to that of the charging cur- 
rent. 

The simplest storage cell is Plante's cell, which, 
as originally constructed, consists of two plates of 



Cel.] 



81 



[Cel. 



lead immersed in dilute sulphuric acid, H 2 S0 4 . 
On the passage of the charging current, the plates 
A and B, Fig 101, dipped in H 2 S0 4 , are covered 
respectively with lead peroxide, Pb0 2 , and finely 
divided, spongy lead. The peroxide is formed on 
the positive plate, and the metallic lead on the 
negative plate. The acid and water should have 
a specific gravity of about 1.170. When the cell 
is fully charged the acid solut : on loses its c eir- 
ness and becomes milky in appearance, and the 





EffiS 



Figs. 101 and 102. 



O isctianjincj? 
Storage Cell. 



specific gravity increases to 1. 195. This increase 
is a good sign of a fall charge. 

When the charging current ceases to pass, the 
cell discharges in the opposite direction, viz., 
from B' to A', that is, from the spongy lead plate 
to the peroxide plate through the electrolyte, as 
shown in Fig. 102. 

As a result of this discharging current the per- 
oxide, Pb0 2 , on A', gives up one of its atoms of 
oxygen to the spongy lead on B', thus leaving 
both plates coated with a layer of PbO, lead 
monoxide, or litharge. When this change is 
thoroughly effected, the cell becomes inert, and 
will furnish no further current until again charged 
by the pa-sage of a current from some external 
source. 

In order to increase the capacity of the storage 
cells, and thus prolong the time of their discharge, 
the coating of lead monoxide thus left on each 
of the plates, when neutral, is made as great as 
possible. To effect this, a process called ' 'forming 
the plates''' is employed, which con ists in first 
charging the plates as already described, and 
then reversing the direction of the charging cur- 
rent, the currents being sent through- the cell in 
alternately opposite directions, until a consider- 
able depth of the lead plates has been acted on. 

It will be noticed that during the action of the 
charging current, the oxygen is transferred from 
the PbO, on one plate, to the PbO, on the other 
plate, thus leaving one Pb, and the other Pb0 2 ; 
and that on discharging, one atom of oxygen is 



transferred from the Pb0 2 , to the Pb, thus leav- 
ing both plates covered with PbO. In reality 
this is but the final result of the action, hydrated 
sulphate of lead, PbO, H 2 S0 4 , being formed 
and subsequently decomposed. Other com 
pounds are formed that are but imperfectly un- 
derstood. 

In order to decrease the time required for form- 
ing, accumu ato.rs, or secondary cells, have been 
constructed, in which metallic plates covered with 
red lead Pb 3 4 replace the lead p'ates in the 
original Plante cell. On charging, the Pb 3 4 
is peroxidized at the anode, i. e., converted into 
Pb0 2 , and deoxidized, and subsequently con- 
verted into metallic lead at the kathode. Or, in 
place of the above Pb 3 4 , red lead is placed on 
the anode and PbO, or litharge, on the kathode. 

Plates of compressed litharge have also been 
recently used for this purpose. Storage cells so 
formed have a greater storage capacity per unit 
weight than those in which a grid is employed, 
but a higher resistance. 

In all cases where a metal plate is employed 
various irregularities of surface are given to the 
plates, in order to increase their extent of surface 
and to afford a means for preventing the separa- 
tion of the coatings. The metallic form thus 
provided is known technically as a grid. 

Unless care is exercised, the plates will buckle 
from the difference in the expansion of the lead 
and its filling of oxide. This buckling is attended 
with an increase in the resistance of the ceil and 
the gradual separation of the oxides that cover or 
fill it. 

Cell, Thermo-Electric — A name 

applied to a thermo-electric couple. (See 
Couple, Thermo-Electric .) 

Cell, Yoltaic The combination of 

two metals, or of a metal and a metalloid, 
which, when dipped into a liquid or liquids 
called electrolytes, and connected outside the 
liquid or liquids by a conductor, will produce 
a current of electricity. 

Different liquids or gases may take the place of 
the two metals, or of the metal and metalloid. 
(See Battery, Gas.) 

Plates of zinc and copper dipped into a solu- 
tion of sulphuric acid and water, and connected 
outside the liquid by a conductor, form a simple 
voltaic cell. 

If the zinc be of ordinary commercial purity, 



Cel.] 



82 



[Cel. 



and is not connected outside the liquid by a con- 
ductor, the following phenomena occur: ' 

(i.) The sulphuric acid or hydrogen sul- 
phate, H 2 S0 4 , is decomposed, zinc sulphate, 
ZnS0 4 , being formed, and hydrogen, H 2 , liber- 
ated. 

(2.) The hydrogen is liberated mainly at the 
surface of the zinc plate. 

(3.) The entire mass of the liquid becomes 
heated. 

If, however, the plates are connected outside 
the liquid by a conductor of electricity, then the 
phenomena change and are as follows, viz.: 

(1.) The sulphuric acid is decomposed as be- 
fore; but, 

(2.) The hydrogen is liberated at the surface of 
the copper plate only. 

(3.) The heat no longer appears in the liquid 
only, but in all parts of the circuit. 

(4.) An electric current now flows through the 
entire circuit, and will continue so to flotv as long 
as there is any sulphuric acid to be decomposed, 
and zinc with which to form zinc sulphate. 

The energy which previously appeared as heat 
only, now appears in part as electric energy. 

Therefore, although the mere contact of the 
two metals with the liquid will produce a differ- 
ence of potential, it is the chemical potential 
energy which became kinetic during chemical 
combination that supplies the energy required to 
maintain the electric current. (See Energy, 
Kinetic. Energy, Potential.) 

A voltaic cell consists of two plates of different 
m< tals, or of a metal and a metalloid (or of two 
gases, or two liquids, or of a liquid and a gas), 
each of which is called a 
voltaic element, and which, 
taken together, form what is 
called a voltaic couple. 

The voltaic couple dips in- 
to a liquid called an electro- 
lyte, which, as it transmits 
the electric current, is de- 
composed by it. The ele- 
ments are connected outside 
the electrolyte by any con- 
ducting material. 

Direction of the Current.— 




Fig. 103. Voltaic 
Couple. 



-In any voltaic cell 
the current is assumed to flow through the liquid, 
from the metal most acted on to the metal least 
acted on, and outside the liquid, through the out- 
side circuit, from the metal least acted on to the 
metal most acted on. 



In Fig. 103 a zinc-copper voltaic couple is 
shown, immersed in dilute sulphui ic acid. Here, 
since the zinc is dissolved by the sulphuric acid, 
the zinc is positive, and the copper negative in 
the liquid. The zinc and copper are of opposite 
polarities out of the liquid. 

There is still a considerable difference of opinion 
as to the exact cause of the potential difference of 
the voltaic cell. There can be no doubt that a 
true contact force exists, but the chemical poten- 
tial energy of the positive plate is the source 
of energy which maintains the potential differ- 
ence. 

• The difference in the polarity of the zinc and 
copper in and out of the liquid is generally de- 
nied by most of the later writers on electricity, 
since tests by a sufficiently delicate electrometer 
show that the entire zinc plate is negative and 
the entire copper plate positive. Remembering, 
however, the convention as to the direction of 
the flow of the current, since the current flows 
from the zinc to the copper through the liquid, 
we may still fairly regard the zinc as positive and 
the copper as negative in the liquid. It will be 
remembered, that \i\ every source the polarity 
within the source is necessarily opposite to the 
polarity outside it. The copper plate is there- 
fore called the negative plate, and the wire con- 
nected to its end out of the liquid, the positive 
electrode. Similarly, the zinc plate is called the 
positive plate, and the wire connected to it the 
negative electrode. 

It will of course be understood that in the 
above sketch the current flows only on the com- 
pletion of the circuit outside the cell; that is, 
when the conductors attached to the zinc and 
copper plites a e electrically connected. 

Amalgamation of the Zinc Plate. —When zinc 
is used for the positive element, it will, unkss 
chemically pure, be dissolved by the electrolyte 
when the circuit is open, or will be irregularly 
dissolved when the circuit is closed, producing 
currents in little closed circuits fi om minute vol- 
taic couples formed by the zinc and such impuri- 
ties as carbon, lead, or iron, etc., always found 
in commercial zinc. (See Action, Local, of Vol- 
taic Cell.) As it is practically impossible to ob- 
tain chemically pure zinc, it is necessary to amal- 
gamate the zinc plate; that is, to cover it with a 
thin layer of zinc amalgam. 

Polarization of the Negative Plate. — Since the 
evolved hydrogen appears at the surface of the 
negative plate, the surface of this plate, unless 



•CelJ 



83 



[Cel. 



means are adopted to avoid it, will, after a while, 
become coated with a film of hydrogen gas, or 
as it is technically called, will become polarized. 
.(See Cell, Voltaic, Polarization of.) 

The effect of this polarization is to cause a fall- 
ing off or weakening of the current produced by 
the battery, due to the formation of a counter - 
electromotive force produced by the hydrogen- 
coveted plate; that is to say, the negative plate, 
now being covered with hydrogen, a very highly 
electro-positive element, tends to produce a 
current in a direction opposed to that of the 
cell proper. (See Eorce, Electromotive, Coun- 
ter.) 

This decrease in current strength is rendered 
still greater by the increased resistance in the ctll, 
due to the bubbles of hydrogen, and to the de- 
creased electromotive force, due to the increase 
in the density of the zinc sulphate, in the case of 
zinc in hydrogen sulphate. 

In the case of storage cells, the counter-elec- 
tromotive force of polarization is employ td as the 
source of secondary currents. (See Electricity, 
Storage of. Cell, Secondary. Cell, Storage.) 

In order to avoid the effects of polarization in 
voltaic cells, and thus insure constancy of cur- 
rent, the bubbles of gas at the negaiive plate are 
mechanically carried off either by roughening its 
surface, by forcing the electrolyte against the 
plate as by shaking, or by a stream of air; or else 
the negative plate is surrounded by some liquid 
or solid substance which will remove the hydro- 
gen, by entering into combination with it. (See 
Cell, Voltaic, Polarization of .) 

Voltaic cells are therefore divided into cells 
with one or wiih two fluids, or electrolytes, or 
into: 

(i.) Single -fluid cells; and 

(2.) Double-fluid cells. 

Very many forms of voltaic cells have been de- 
vised. The following are among the more im- 
portant, viz. : Of the Single-Fluid Cells, the 
Grenet, Poggendorff, or Bichromate, the Zinc 
Copper, the Zinc- Carbon and the Smee. Of the 
Double- Fluid Cells, Grove's, Bunsens, Callaud 
or Gravity, Daniel? s, Leclanche, Siemens-Halske 
and the Meidinger. 

Of all the voltaic cells that have been devised 
two only, viz., the Gravity, a modified Daniell, 
and the Leclanche, have continued until now in 
very general use, the gravity cell being used on 
closed-circuited lines, and the Leclanche on open- 
circuited lines ; the former being the best suited 



of all cells to furnish the continuous constant cur- 
rents employed in most systems of telegraphy, 
and the latter for furnishing the intermittent cur- 
rents required for ringing bells, operating annun- 
ciators, or for similar work. 

Cell, Voltaic, Absorption and Genera- 
tion of Heat in (See Heal, Absorption 

and Generation of, in Voltaic Cell.) 

Cell, Voltaic, Bichromate A zinc- 
carbon couple used with an electrolyte 
known as electropoion, a solution of bichro- 
mate of potash and sulphuric acid in water. 
(See Liquid, Electropoion) 

Bichromate of sodium or chromic acid are 
sometimes used instead of the bichromate of 
potassium. 

1 he zinc, Fig. 104, is amalgamated and placed 
between two carbon plates. 
The terminals connected 
with the zinc and carbon 
are respectively negative 
and positive. In the form 
s-hovvn in the figure, the zinc 
p ate can be lilted out of 
the liquid when the cell is 
not in action. 

The bichromate cell is 
excellent for purposes re- 
quiring strong currents 
where long action is not 
necessary. As this cell 
readily polarizes it cannot 
be advantageously employ- 
ed continuously for any 
considerable period of time. It becomes depolar- 
ized, however, when left for some time on open 
circuit. 

The following chemical reaction probably takes 
place when the cell is furnishing current, viz. : 
K 2 Cr,0 7 + 7H 2 S0 4 -f 3Zn = 

K 2 S0 4 + 3 ZnS0 4 + Cr 2 3(So 4 ) + 7H 2 0. 

This cell gives an electromotive force of about 
1.9 volts. 

Cell, Voltaic, Bunsen's A zinc- 
carbon couple, the elements of which are 
immersed respectively in electrolytes of dilute 
sulphuric and strong nitric acids. 

Bunsen's cell is the same as Grove's, except 
that the platinum is replaced by carbon. The 
zinc surrounds the porcus cell containing the car- 




104. Bichromate 
Cell. 



CeL] 



84 



[CeL 



bon. The polarity is as indicated in Fig. 105, 
(See Cell> Voltaic, Grove.) 




Fig. fOJ. Bunsen Cell. 

The Bunsen cell gives an electromotive force 
of about 1.96 volts. 

Cell, Toltaic, Callaud's A name 

sometimes given to the gravity cell. (See 
Cell, Voltaic, Gravity) 

Cell, Yoltaic, Capacity of Polarization of 

The quantity of electricity required 

to be discharged by a voltaic cell in order to 
produce a given polarization. (See Cell, Vol- 
taic, Polarization of.) 

During the discharge of a voltaic cell an electro- 
motive iorce is gradually set up that is opposed 
to that of the cell. The quantity of electricity 
required to produce a given polarization de- 
pends, of course, on the condition and size of 
the plates. Such a quantity is called the capacity 
of polarization. 

Cell, Yoltaic, Closed-Circuit A 

voltaic cell that can be left for a considerable 
time on a closed circuit of comparatively 
small resistance without serious polarization. 

The term closed-circuit voltaic cell is used in 
contradistinction to open- circuit cell, and applies 
to a cell that can only be kept on closed circuit 
for a comparatively short time. 

Daniell's cell and the gravity cell are closed-cir- 
cuit cells. Leclanche's is an open-circuit cell. 

Cell, Yoltaic, Contact Theory of 

A theory which accounts for the production 
of difference of potential or electromotive 
force in the voltaic cell by the contact of the 
elements of the voltaic couple with one an- 
other by means of the electrolyte. 



The mere contact of two dissimilar substances 
through the electrolyte will produce a difference 
of potential, but the cause of the current which a- 
voltaic cell is able to maintain is the chemical 
potential energy which becomes kinetic during: 
combination. (See Cell, Voltaic. Series, Contact.)- 

Most authorities explain the difference of 
potential produced by the contact of different 
metals by the fact that the metals are sur- 
rounded by air. They point out the fact that the 
order of the metals in the contact-series is 
almost identical with the order of their electro- 
chemical power as deduced from their chemical 
equivalents, and their heat of combination with 
oxygen. It would appear, therefore, that the 
difference of potential between a metal and the 
air which surrounds it, is a measure of the tend- 
ency of the metal to become oxidized. 

The origin of the electromotive force of a zinc- 
copper couple, in an electrolyte of hydrogen sul- 
phate, is the superior affinity of the zinc for the 
oxygen, over that of the copper for the oxygen. 

Cell, Yoltaic, Creeping in The 

formation, by efflorescence, of salts on the sides 
of the porous cup of a voltaic cell, or on the 
walls of the vessel containing the electrolyte. 
Paraffining the portions of the walls out of the 
liquid, or covering the surface of the liquid with 
a neutral oil, obviates much of this difficulty. (See 
Efflorescence.) 

Cell, Yoltaic, Daniell's A zinc- 
copper couple, the elements of which are im- 
mersed respectively in electrolytes of dilute 
sulphuric acid, and a saturated solution of 
copper sulphate. 

In the form of Daniell's cell, shown in Fig. 106, 
the copper element is made in the form of a cylin- 
der c, and is placed in a porous cell. The cop- 
per cylinder is provided with a wire basket near 
the top, filled with crystals of blue vitriol, or cop- 
per sulphate, so as to maintain the strength of the 
solution while the cell is in use. The zinc is in 
the shape of a cylinder and is placed so as to sur~ 
round the porous cell. This cell gives a nearly 
constant electromotive force. 

The constancy of action of Daniell's cell 
depends on the fact that for every molecule oi 
sulphuric acid decomposed in the outer cell, an 
additional molecule of sulphuric acid is supplied 
by the decomposition of a molecule of copper sul- 
phate in the inner cell. This will be better un- 



CeL] 



85 



[Cel. 



derstood from the following reactions which take 

place, viz.: 

Zn+H 2 S0 4 = ZnS0 4 + H 2 
H 3 + CuS0 4 = H 3 S0 4 -f- Cu. 
The H 2 S0 4 , thus formed in the inner cell, 

passes through the porous cell, and the copper is 

deposited on the surface of the copper plate. 




Fig 1 06. Daniell s Cell. 

The Daniell cell gives an electromotive force 
of about 1.072 volts. 

A serious objection to this form of cell arises 
from the fact that the copper is gradually de- 
posited over the surface and in the pores of the 
porous cell, thus greatly increasing its resistance. 
This difficulty is avoided in the gravity cell. (See 
Cell, Voltaic ; Gravity.) 

Cell, Yoltaic, Double-Fluid A 

voltaic cell in which two separate fluids or elec- 
trolytes are employed. 

One of the elements of the voltaic couple is 
dipped into one of the fluids and the other ele- 
ment into the other fluid. In order to keep the 
fluids separate and distinct, they are either sep 
arated by means of porous cells, or by the action 
of gravity. (See Cell, Porous. Cell, Voltaic, 
Gravity.) 

In the double-fluid cell the negative element is 
surrounded by a liquid which is capable of pre- 
venting polarization by combining chemically 
with the substance that tends to collect on its 
surface. In the Daniell cell this substance is the 
same as that of the negative plate. (See Cell, 
Voltaic, Polarization of.) 

Cell, Yoltaic, Dry A voltaic cell 

in which a moist material is used in place of 
the ordinary fluid electrolyte. 



The term dry cell is in reality a misnomer, 
since all such cells are moistened with liquid 
electrolytes. 

The dry cell, like other cells, is made in a 
variety of forms. The ab- 
sence of free liquid permits 
the cell to be closed. A well 
known form of dry cell is 1 
shown in Fig. 107. 

Cell, Yoltaic, Effects of 

Capillarity in (See 

Capillarity.. Effects of, in 
Voltaic Cell.) 

Cell, Yoltaic, Exciting 
Liquid of The elec- 
trolyte Of a VOltaic Cell. Fig , TO y. Dry Cell 

A voltaic cell may have a single electrolyte, in 
which case it is called a single-fluid cell, or it may 
hav-e two electrolytes, in which case it is called a 
double- fluid cell. 

Cell, Yoltaic, Fuller's Mercury Bichro- 
mate — A zinc-carbon couple im- 
mersed in an electrolyte of electropoion liquid. 

The zinc is attached to a copper rod by being 
cast thereto, and is placed at the bottom of a 
porous cell, where it is covered by a layer of: 
mercury. The carbon plate is placed in electro- 





Fig. 108 Fuller's Mercury Bichromate Cell. 
poion liquid, diluted with water in the proportion 
of three ot the former to two of the latter. The 
zinc is generally placed in pure water, which 
rapidly becomes acid. 

The mercury effects the continuous amalgama- 
tion ol the zinc. 

A Fuller mercury bichromate cell is shown 
in Fig. 108. 



Cel.] 



86 



ECeL 



Cell, "Voltaic, Gravity —A zinc- 
copper couple, the elements of which" are em- 
ployed with electrolytes of dilute sulphuric acid 
-or dilute zinc sulphate, and a concentrated 
solution of copper sulphate respectively. 

The use of a porous cell is open to the objection 
of increased internal resistance. Moreover, the 
porous cell is apt to receive a coating of copper 
which often deposits on the cell instead of on the 
copper plate. The gravity cell was devised in 
order to avoid the use of a porous cell. As its 
name indicates, the two fluids are separated from 
each other by gravity. 

The copper plate is the lower plate, and is sur- 
rounded by crystals of copper sulphate. The 
zinc, generally in the form of an open wheel, or 
crow-foot, is sus- 
pended near the top 
of the liquid, as 
shown in Fig. 109. 

When the cell is 
set up with, sul- 
phuric acid, the re- 
actions are the same 
as in the Daniell 
cell. When copper 
sulphate and zinc 
sulphate alone are 
used, zinc replaces 
the copper in the 
copper sulphate. 
The action is then 
merely a substitution process 
DanielPs.) 

A dilute solution of zinc sulphate is generally 
used to replace the dilute sulphuric acid. It 
gives a somewhat lower electromotive force, but 
ensures a greater constancy for the cell. 

Cell, Yoltaic, Grenet A name 

sometimes given to the bichromate cell. (See 
Cell. Voltaic, Bich? ornate) 

Cell, Voltaic, Grove —A zinc-plati- 
num couple, the elements of which are used 
with electrolytes of sulphuric and nitric acids 
respectively. 

The zinc, Z, Fig. 1 10, is amalgamated and 
placed in dilute sulphuric acid, and the platinum, 
P, in strong nitric acid (HN0 3 ) in a porous cell 
to separate it from the sulphuric acid. (See Cell, 
Porous.') In the Grove cell the current is moder- 
ately constant, since the polarization of the plati- 




Fig. ioq The Gravity Cell. 
(See Cell, Voltaic, 



num plate is prevented by the nitric acid, which 
oxidizes and thus removes the hydrogen that 
tends to be liberated at its surface. The con- 
stancy of the current 
is not maintained for 
any considerable time, 
since the two liquids 
are rapidly decom- 
posed, or consumed, 
zinc sulphate forming 
in the sulphuric acid, 
and water in the nitric 
acid. 

The chemical reac- 
tions are as follows, 



ZnS0 4 -f H 2 ; 
6H + 2HN0 3 = 

4H s O + 2NO; 
2NO + 2 = N 2 4 . 

Nitrate of ammo- 
nium is sometime; formed when the nitric acid 
becomes dilute by decomposition. The reaction 
is as follows : 

2HNO3 -f 4 H 2 = 3H 2 + NH 4 NO g . 

The cell gives an electromotive force of 1.93 
volts. 

When the porous cell is good, the resistance of 
the Grove cell may be calculated according to 
the following formula of Ayrton: 

3-6 X d 




Grove' i 



R = 



ohms, 



where d, is the distance in inches between the 
platinum and zinc plates, and A, the square inches 
of the immersed portion of the platinum plate. 

Cell, Voltaic, Leclanclie A zinc- 
carbon couple, the elements of which are used 
in a solution of sal-ammoniac and a finely 
divided layer of black oxide of manganese 
respectively. 

The zinc is in the form of a slender rod and 
dips into a saturated solution of sal-ammoniac, 
NH 4 C1. 

The negative element consists of a plate of car- 
bon, C, Fig. in, placed in a porous cell, in which 
is a mixture of black oxide of manganese and 
broken gas-retort carbon, tightly packed around 
the carbon plate. By this mean? a greatlv ex 
tended surface of carbon surrounded by black 



CeL>] 

oxide of manganese, MnO g , is secured. The entire 
outer jar, and the spaces inside the porous cell are 
filled with the solution of sal-ammoniac. 



87 




The Leclanche Cell. 



This cell, though containing but a single fluid, 
belongs, m reality, to the class or type of double- 
fluid cells, being one in which the negative ele- 
ment is surrounded by an oxidizing substance, 
the black oxide of manganese, which replaces the 
nitric acid or copper sulphate in the other double- 
fluid cells. 

This reaction is generally given : 

Zn + 4 NH 4 C1 -f 2Mn0 2 = ZnCl s + 2 NH 4 C1 
-j- 2NH 3 + Mn 8 O s + H 8 0- 

This reaction is denied by some, who believe 
the following to take place : 

Zn + 2(NH 4 C1) = ZnCl 3 + 2NH3 + H 2 . 
The ZnCl 2 and NH 3 react as follows : 
ZnCl 2 -f 2(NH 3 ) = 2 (NH 2 ) ZnCl 2 + H 2 . 
2H -f 2(Mn 2 2 ) == H 2 -J- Mn 2 Q 3 ; 
-or, possibly, 4H -f- 3MnO a = Mn 2 -f- 2H 2 0. 

The Leclanche cell gives an electromotive force 
of about 1.47 volts. It rapidly polarizes, and 
cannot, therefore, give a steady current for any 
prolonged time. When left on open circuit, how- 
ever, it quickly depolarizes. 

Cell, Voltaic, Local Action of 

(See Action, Local, of Voltaic Cell.) 

Cell, Toltaic, Meidinger A zinc- 
copper couple, the elements of which are em- 
ployed with dilute sulphuric acid, or solution 
of sulphate of magnesia, and strong nitric 
acid, respectively. 

The Meidinger cell is a modification of the 
Daniell cell. The zinc-copper couple is thus ar- 
ranged : Z Z, Fig. 112, is an amalgamated zinc 
ring placed near the walls of the vessel, A A, 
constricted at b b. The copper element, c, is 
similarly placed with respect to the walls of the 
vessel d d. The glass cylinder h, filled with 




[Cel. 

crystals of copper sulphate, has a small hole in 
its bottom, and keeps the vessel, d d, supplied 
with saturated so- 
lution of copper 
sulphate. The cell 
is charged with di- 
lute sulphuric acid, 
or a dilute solution 
of Epsom salts, or 
magnesium sul- 
phate. 

Cell, Voltaic, 
Open -Circuit 

A voltaic 

cell that cannot be 
kept on closed cir- 
cuit, with a com- 
paratively small 

resistance, for any Fig. 112. The Meidinger Cell. 

considerable time without serious polariza- 
tion. 

A Leclanche cell is an open-circuit cell. The 
term open-circuit cell is used in contradistinc- 
tion to closed-circuit cell, such as the Daniell. 
(See Cell, Voltaic, Closed-Circuit.) 

Cell, Voltaic, Pog-gendorff —A 

name sometimes given to the Grenet cell. (See 
Cell, Voltaic, Grenet) 

Cell, Voltaic, Polarization of The 

collection of a gas, generally hydrogen, on the 
surface of the negative element of a voltaic 
cell. 

The collection of a positive substance like hydro- 
gen on the negative element or plate of a voltaic 
cell sets up a counter-electromotive force, which 
tends to produce a current in the opposite direc- 
tion to that produced by the cell. (See Force, 
Electromotive, Counter.) 

Polarization causes a decrease in the normal 
current of a voltaic cell: 

(1.) On account of the increased resistance of 
the cell from the bubbles of gas which form part 
of its circuit. 

(2.) On account of the counter -electromotive 
force, produced by polarization. 

There are three ways in which the ill effects of 
the polarization of a voltaic cell can be avoided. 
These are : 

(1.) Mechanical. — The negative plate is fur- 
nished with a roughened surface which enables the 



Cel.] 



88 



[CeL 



bubbles of gas to escape from the points on such sur- 
face ; or, a stream of gas, or air, is blown through 
the liquid against the plate and thus mechanically 
brushes the bubbles off. 

(2.) Chemical. — The surface of the negative 
plate is surrounded by some powerful oxidizing 
substance, such as chromic or nitric acid, which 
is capable of oxidizing the hydrogen, and thus 
thoroughly removing it from the plate. 

The oxidizing substance may form the entire 
electrolyte, as is the case of the bichromate solution 
employed in the zinc-carbon couple. Generally, 
however, it has been found preferable to employ 
a separate liquid, like nitric acid, to completely 
surround the negative plate, and another liquid for 
the positive plate, the two liquids being generally 
kept from mixing by a porous cell, or diaphragm. 
Such cells are called double -fluid cells. (See 
Cell, Voltaic, Double -Fluid.) 

(3.) Electro-Chemical. — This also necessitates a 
double-fluid cell. The negative element is im- 
mersed in a solution of a salt of the same metal as 
that forming the negative plate. Thus, a cop- 
per plate, immersed in a solution of copper sub 
phate, cannot be polarized, since metallic copper 
is deposited on its surface by the action of the 
hydrogen which tends to be liberated there. 

The constancy of action of a Daniell cell depends 
on a deposition of metallic copper on its copper 
plate as well as on the formation of hydrogen 
sulphate, and the solution of additional copper 
sulphate from the crystallized salt placed in the 
cell. (See Cell, Voltaic, Daniell 's.) 

Cell, Toltaic, Primary, Exhaustion of 

The inability of a primary voltaic 

cell to furnish any further current, unless 
fresh electrolyte, or fresh positive element, or 
both, are supplied to it. 

In the case of exhaustion of a primary voltaic 
cell the stock of fresh energy is supplied to the 
cell from the chemical potential energy of the 
positive element, or of the electrolyte or elec- 
trolytes. (See Energy, Chemical Potential.') 

In most voltaic cells a marked decrease in the 
current strength is observed soon after the cir- 
cuit is closed, and, therefore, long before the 
cell is exhausted. This decrease is due — 

(1.) To the increased internal resistance due to 
the bubbles of hydrogen on the negative plate. 

(2.) To the counter-electromotive force of po- 
larization, where zinc is employed with an elec- 
trolyte of sulphuric acid. 



(3.) To the decrease in the electromotive force 
due to an increase in the density of the zinc sul- 
phate. 

Cell, Voltaic, Secondary, Exhaustion of 

The inability of a secondary cell to- 

furnish any further current, unless fresh 
electro-positive and electro-negative materials 
are formed in it by the passage of the 
charging current. 

In the case of the exhaustion of a secondary 
voltaic cell, the stock of fresh energy supplied 
to the cell is derived fro n the electric energy 
of the charging current. (See Energy, Electric.) 

Cell, Voltaic, Siemens-Halske 

A zinc-copper couple, the elements of which 
are employed with dilute sulphuric acid and 
saturated solution of copper sulphate respect- 
ively. 

The Siemens-Halske cell is a modification of 
Darnell's. A ring of zinc, Z Z, Fig. 113, sur- 




Fig 1 13. Siemens-Halske Cell. 

rounds the glass cylinder, c c. The porous 
cell is replaced by a diaphragm, f f, of porous 
paper, formed by the action of sulphuric acid on 
a mass of paper pulp, Crystals of copper sul- 
phate are placed in the glass jar, c c, and rest 
on the copper plate, k, formed of a close copper 
spiral. Terminals are attached at b and h. The 
entire cell is charged with dilute sulphuric acid^ 
The resistance of the cell is high . 

Cell, Voltaic, Silver Chloride A 

zinc and silver couple immersed in electro- 
lytes of sal-ammoniac or common salt and 
silver chloride. 



€el.] 



89 



[CeL 



The zinc acts as the positive element, and a 
silver wire, around which a cylinder of fused 
silver chloride is cast, as the negative element. 
The zinc, and the silver wire and silver chloride, 
are placed in a small glass test-tube and covered 
with the sal-ammoniac or common salt, and 
the tube closed by a cork of paraffin, to prevent 
the evaporation of the electrolyte. When sal- 
ammoniac is used, the strength of the solution is 
that obtained by dissolving 23 grammes of pure 
sal-ammoniac in I litre of water. The silver 
chloride acts as a depolarizer. 

This cell is used as a standard cell, known as 
De la Rue's standard cell, from its inventor, 
Warren De la Rue. Its electromotive force is 
1.068 volts. 

Cell, Toltaic, Simple Any voltaic 

cell formed of a single couple immersed in a 
single exciting liquid. 



Cell, Voltaic, Single-Fluid 



-A vol- 



taic cell in which but a single fluid or elec- 
trolyte is used. 

Single-fluid voltaic cells possess the disadvan- 
tage of polarizing during action. This polariza- 
tion is due to the electro-positive element of the 
electrolyte collecting on the surface of the nega- 
tive plate, or within its ma=s. For example, 
where dilute sulphuric acid is the electrolyte, 
hydrogen gas collects on the negative plate and 
lowers the electromotive jorce produced by the 
•cell, by a counter- electromotive force thereby 
generated. (See Force, Electromotive. Force, 
Electromotive, Counter.') 

Cell, Toltaic, Smee A zinc-silver 

couple used with an electrolyte of dilute sul- 
phuric acid, H 2 S0 4 . 

A form of Smee cell is shown in Fig. 1 14. Here 
the plate of silver is placed between two zinc 
plates. 

The silver plate is roughened and covered with 
a coating of metallic platinum, in the condition 
known as platiniwi black. (See Platinum Black.) 
This cell was formerly extensively employed in 
electro-metallurgy but is now replaced by dynamo- 
electric-machines. (See Metallurgy, Electro. 
Machine, Dynamo -Electric. ) 

A zinc carbon couple is sometimes used to re- 
place the zinc -silver couple. A couple of zinc 
lead is also used, though not very advanta- 
geously. 



The Smee cell was one of the earliest forms 
of voltaic cells. 

In the zinc-silver couple the chemical reaction 
that takes place when the 
cell is furnishing current is 
as follows, viz. : 
Zn -f H 2 S0 4 = ZnS0 4 

+ H 2 . 

The Smee cell gives an 
electromotive force of about 
.65 volt. 



Cell, 
ard — 



Voltaic, Stand- 

A voltaic cell 




the electromotive force of 
which is constant, and Fig. 114. Smee Cell. 
which, therefore, may be used in the measure- 
ment of an unknown electromotive force. 

Absolute constancy of electromotive force is 
impossible to attain, but if the current of the 
standard cell is closed but for a short time the 
electromotive force may be regarded as practically 
invariable. 

Cell, Voltaic, Standard, Clark's 

The form of standard cell shown in Fig. 115. 
Latimer Clark's standard cell assumes a 
variety of forms. The H-form is arranged as 
shown in Fig. 115. The vessel to the left con- 
tains, at A, an amal- 
gam of pure zinc. The 
other vessel contains, 
at M, mercury covered 
with pure mercurous 
sulphate, Hg 2 S0 4 . 
Both vessels are then 
filled, above the level 
of the cross tube, with 
a saturated solution of 
zinc sulphate Z, Z, to 
which a few crystals 
of the same are added. 
Tightly fitting corks 
C, C, prevent loss by 
evaporation. 




Clark's Stand- 



Fig, iij. 

ard Cell. 

The voltage of this cell in legal volts is 1.438 
[1 — 0.00077 (t — 15 degrees C.)]— (Ayrton.) 

The value t, is the temperature in degrees of 
the centigrade scale. 

Cell, Voltaic, Standard, Rayleigh's Form 

of Clark's A modified form of Clark's 

cell. 



Cel.] 



90 



[Cel. 



Lord Rayleigh's form of Clark's standard cell 
is shown in Fig. 1 16. The electrodes pass respect- 
ively through the bottom and top of the test tube 
of glass. On the lower 
electrode a layer of mer- 
cury, Hg, is placed. On 
this rests a layer of mercu- 
rous sulphate paste made 
sufficiently semi-fluid with 
a solution of zinc sulphate 
to form an approximately 
level surface. The zinc, 
Zn, is attached to the up- 
per electrode and is im- 
mersed in this semi-fluid 
paste. 

The mercurous sulphate 
appears to act to keep the 
mercury free from impuri- 
ties. 

The electromotive force g 
of this cell has been care- 
fully determined by Ray- ^ J/6 Ray leigh's 
leigh. Its value in true Form of Clark's 

volts is : Standard Cell. 

E= 1.435 i 1 — .00077 It— 15)] when t, is the 
temperature in degrees Centigrade. 

This cell is often called Clark's normal element. 

Cell, Voltaic, Standard, De la Rue's 

—A form of silver-chloride cell. (See Cell, 
Voltaic, Silver-Chloride?) 

Cell, Voltaic, Stand- 
ard, Fleming's 




The form of standard 
cell shown in Fig. 1 17. 
The U-tube, Fig. 117, 
is connected, as shown, 
by means of taps, with 
two vessels filled with 
chemically pure solutions 
of copper sulphate of sp. 
gr. 1.1 at 15 degrees C, 
and zinc sulphate of sp. 
gr. 1.4 at 15 degrees C. 
respectively. To use the 
cell the zinc rod Zn, con- 
nected with a wire pass- 
ing through a rubber Fig. 117- Fleming's 
stopper, is placed in the Standard Cell. 

left-hand branch. The tap A, is opened and 
the entire U-tube is filled with the denser 
zinc sulphate solution. The tap at C, is then 




opened, and the liquid in the right-hand branch 
above the tap is discharged into the lower vessel, 
but, from this part only. The tap C, is then 
closed, and the tap B, opened, and the lighter 
copper sulphate allowed to fill the right-hand 
branch above the tap C. The copper rod Cu, fitted 
to a rubber stopper and connected with a con- 
ducting wire, is then placed in the copper solution. 

Tubes are provided at L and M, for the recep- 
tion of the zinc and copper rods when not in use. 
The copper rod is prepared for use by freshly 
electro-plating it with copper. The electro- 
motive force of this cell is 1.074 volts. If the line 
of demarkation between the two liquids is not 
sharp, the arms of the vessels are emptied, and 
fresh liquid is run in. 

Cell, Voltaic, Standard, Lodge's 

A form of standard Daniell cell. 

Lodge's standard cell is shown in Fig. 118. 
Through the tube T, in a 
wide mouthed bottle, is 
passed the glass tube, in the 
mouth of which is placed a 
zinc rod. To the bottom of 
the tube T, a small test-tube 
t, containing crystals of cop 
per sulphate, is fastened by 
means of a string or rubber 
band. The uncovered end 
of a gutta-percha insulated 
copper wire projects at the 
bottom of t, through a tube 
in a tightly fitting cork, and 
forms the copper electrode. The bottle is partly 
filled as shown with a solution of zinc sulphate. 

The internal resistance of this cell is so high 
that it is only employed in the use of zero methods 
with a condenser. 

Cell, Voltaic, Standard, Sir William 

Thomson's — A form of standard 

Daniell cell. 




Fig. 118. Lodge's 
Form of Daniell' s Cell. 




Fig. ug. Thomson' s Form of DanLll's CelL 
Sir Wm. Thomson's standard cell is shown in 
Fig. 119. A zinc disc is placed at the bottom of the 



del.] 



91 



[Cha 



cylindrical vessel and a solution of zinc sulphate 
of sp. gr. 1.2 poured over it. By means of the 
funnel F, a half-saturated solution of copper 
sulphate is carefully poured over this and floats 
on it owing to its smaller density. The electro- 
motive force of this cell is 1.072 true volts at 
15 degrees C. 

Cell, Toltaic, Standardizing a De- 
termining the exact value of the electromotive 
force of a voltaic cell, in order to enable it to 
be used as a standard in determining the 
electromotive force of any other electric 
source. 

Cell, Voltaic, Two-Fluid A term 

sometimes employed in place of double-fluid 
cell. (See Cell, Voltaic, Double-Fluid?) 

Cell, Toltaic, Water A voltaic 

cell in which the exciting liquid is merely 
water. 

Any voltaic couple can be used, the positive 
element of which is acted on by water. (See 
Battery, Voltaic.) 

Cell, Toltaic, Zinc-Carbon —A 

cell in which zinc and carbon form the posi- 
tive and negative elements respectively. 

A name sometimes given to the bichro- 
mate cell. 

Cell, Toltaic, Zinc-Copper —A 

cell in which zinc and copper form the posi- 
tive and negative elements respectively. 

Cell, Toltaic, Zinc-Lead A zinc- 

lead couple sometimes used, though not very 
advantageously, to replace the zinc-silver 
couple in a Smee cell. (See Cell, Voltaic, 
Sinee?) 

Cells, Coupled A number of sep- 
arate cells connected in any way so as to 
form a single source. 

Cells, Toltaic, Series-Connected 



A number of separate voltaic cells connected 
in series so as to form a single source. (See 
Circuit, Series.) 

Cement-Lined Conduit. — (See Conduit, 
Cement-Li?ted.) 

Cements, Insulating- —Various 

mixtures of gums, resins and other substances, 
possessing the ability to bind two or more 



substances together and yet to electrically in- 
sulate one from the other. 

Centi. — (As a prefix) — The one-hundredth 
part of. 

Centi-Ampere. — One-hundredth of an am- 
pere. 

Centi- Ampere Balance. — (See Balance, 
Centi-Ampere.) 

Centigrade Thermometer Scale. — (See 
Scale, Centigrade Thermometer?) 

Centigramme. — The hundredth of a 
gramme 

One centigramme equals 0.1544 grains avoir- 
dupoise. (See Weights and Measures, Metric 
System of.) 

Centilitre. — The hundredth of a litre. 
One centilitre equals 0.6102 of a cubic inch. 
(See Weights and Measures, Metric System of.) 

Centimetre. — The hundredth of a metre. 
One centimetre equals 0.3937 inch. (See 
Weights and Measures, Metric System of. ) 

Centimetre-Gramme-Second Units. — (See 
Units. Centimetre-Gramme-Second.) 

Central Galvanization. — (See Galvaniza- 
tion, Central?) 

Central Station. — (See Station, Central) 

Central Station Burglar Alarm. — (See 
Alarm, Burglar, Central Station.) 

Central Station Lighting. — (See Light- 
ing, Electric Central Station?) 

Centre of Gravity. — (See Gravity, Centre 
of) 

Centre of Oscillation. — (See Oscillation, 
Centre of.) 

Centre of Percussion. — (See Percussion, 
Centre of.) 

Centrifugal Force. — (See Force, Centrifu- 
gal) 

Centrifugal Governor. — (See Governor, 
Centrifugal?) 

Chain Lightning. — (See Lightning, 
Chain?) 

Chain, Linked Magnetic and Electrie 

A chain of three links, the separate 

links of which consist of the primary circuit,, 



Cha.] 



02 



[Cha. 



the magnetic circuit, and the secondary cir- 
cuit respectively, of an induction coil. 

The conception of a linked magnetic and elec- 
tric chain, in studying the action of an induction 
coil, was first developed by Kapp. A linked 
magnetic and electric chain is shown in Fig. 120. 




primary' w 
circuit 



SECONDARY 

CIRCUIT 



Fig. 120, Linked Magnetic and Electric Chain. 

If, in such a case, the magnetic core or circuit is 
of varying magnetization, when one of the electric 
circuits has a periodic current passed through 
it, the various phenomena of the induction coil 
are produced. (See Coil, Induction.) 

Chain, Molecular A polarized chain 

of molecules that is supposed to exist in an 
electrolyte during its electrolytic decomposi- 
tion, or in a voltaic cell on closing its circuit. 
(See Hypothesis, Grotthus) 

Chain Pull.— (See Pull, Chain.) 

Chamber, Armature The armature 

bore. (See Bore. Ar?nature) 

Chamber of Lamp. — (See Lamp, Cham- 
ber of) 

Change, Chemical Any change in 

matter resulting from atomic combination 
and the consequent formation of new mole- 
cules. 

Some chemical changes are caused by atomic 
combinations and the formation of new molecules. 
They are necessarily attended by 3 loss of the spe- 
cific identity of the substances involved in the 
change. Thus carbon, a black solid, combined 
with sulphur, a yellow solid, produces carbon 
disulphide, a colorless, odorous liquid. (See 
Atom.) 

Change, Physical —Any change in 

matter resulting from a change in the relative 
position of its molecules, without the forma- 
tion of new molecules. 

Ice, when heated, is turned into water; steel, 
when stroked by a magnet, is rendered perma- 
nently magnetic; a piece of vulcanite or hard 



rubber" stroked by a piece of cat skin becomes 
electrified. In all these cases, which are instances 
of physical changes, the substances retain their 
specific identity , This is true in all cases of phys- 
ical changes. (See. Molecule.) 

Changing-over Switch. — (See Switch, 
Changing-over) 

Changing Switch. — (See Switch, Chang- 
ing.) 

Characteristic Curve. — (See Curve, 
Characteristic.) 

Characteristic Curve of Parallel Trans- 
former. — (See Curve, Characteristic, of 
Parallel Transformer) 

Characteristic Curve of Series Trans- 
former. — (See Curve, Characteristic, of 
Series Transformer) 

Characteristics of Sound.— (See Sound, 
Characteristic of) 

Charge, Bound The condition of 

an electric charge on a conductor placed near 
another conductor, but separated from it by 
a medium through which electrostatic induc- 
tion can take place. (See Induction, Elec- 
trostatic) 

When a charged conductor is placed near an- 
other conductor, but separated from it by a di- 
electric or medium through which induction can 
take place, a charge of the opposite name is in- 
duced in the neighboring conductor. This charge 
is so held or bound on the conductor by the mu- 
tual attraction of the opposite charge that it is 
not discharged on connection with the earth 
unless both conductors are simultaneously touched 
by any good conductor. The bound charge was 
formerly called dissinndated or latent electricity . 
(See Electricity, Dissimulated or Latent. ) 

Charge, Density of —The quantity 

of electricity per unit of area at any point on 
a charged surface. 

Coulomb used the phrase surface density to 
mean the quantity of electricity per unit of area 
at any point on a surface. 

Charge, Dissipation of The gradual 

but final loss of any charge by leakage, which 
occurs even in a well insulated conductor. 

This loss is more rapid with negatively charged 
conductors, than with those positively charged. 



Cha.] 



93 



[Chi 



Crookes, of England, has retained a charge on 
conductors for years, without appreciable leakage, 
by placing the conductors in vessels in which a 
high vacuum was maintained. (See Vacuum, 
High.) 

Charge, Distribution of —The vari- 
ations that exist in the density of an electrical 
charge at different portions of the surface of 
all insulated conductors except spheres. 

The density of charge varies at different points 
of the surface of conductors of various shapes. It 
is uniform at all points on the surface of a sphere. 

It is greater at the extremities of the longer 
axis of an egg-shaped body, and greatest at the 
sharper end. 

It is greater at the corners of a cube than at 
the middle of a side. 

It is greatest around the edge of a circular disc. 

It is greatest at the apex oi a cone. 

Charge, Electric The quantity of 

electricity that exists on the surface of an in- 
sulated electrified conductor. 

When such a conductor is touched by a good 
conductor connected with the earth, it is dis- 
charged. (See Condenser.) 

Charge, Free The condition of an 

electric charge on a conductor isolated from 
any other conductor. 

It is impossible to obtain a perfectly free charge, 
•since it is impossible to completely isolate an 
insulated conductor. The charge, however, can 
be comparatively free. 

The charge, on a completely isolated conductor., 
readily leaves it when it is put in contact with a 
good conductor connected with the ground. (See 
Charge, Bound.) 

Charge, Induced Electrostatic 

The charge produced by bringing a body 
into an electrostatic field. 

In order to obtain a permanent charge, i. <?., a 
charge which will be maintained when the body 
is withdrawn from an electrostatic field, it is nec- 
essary to connect the body with the earth so that 
it may lose, or part with a charge of the same 
name as the inducing charge. Then, on the with- 
drawal of this charge, it wiH possess a charge op- 
posite in name to the inducing charge. (See 
Condenser.) 

Charge, Influence A charge pro- 



duced by electrostatic induction. (See In- 
duction, Electrostatic^) 

Charge, Negative According to the 

double-fluid hypothesis, a charge of negative 
electricity. 

According to the single-fluid hypothesis, 
any deficit of an assumed electrical fluid. 

Charge, Positive According to the 

double-fluid hypothesis, a charge of positive 
electricity. 

According to the single-fluid hypothesis, 
any excess of an assumed electrical fluid. 

Charge, Kesidual —The charge pos- 
sessed by a charged Leyden jar for a few 
moments after it has been disruptively dis- 
charged by the connection of its opposite 
coatings. 

The residual charge is probably due to a species 
of dielectric strain, or a strained position of the 
molecules of the glass caused by the charge. 
Such residual charge is not present in air con- 
densers. In other words, a Leyden jar does not 
give up all the electric energy charged in it, on a 
single disruptive discharge. 

Charge, Return A charge induced 

in neighboring conductors by a discharge of 
lightning. 

Under the influence of induction a lightning 
stroke produces during its discharge an electric 
shock in the human body, or a charge in neigh- 
boring bodies, which is called the back or re- 
turn stroke of lightning. (See Stroke, Light- 
ning, Back or Return.) 

Charged Body.— (See Body, Charged^ 

Charging Accumulators. — Sending an 
electric current into a storage battery for the 
purpose of rendering it an electric source. 

There is, strictly speaking, no accumulation of 
electricity in a storage battery, such, for example, 
as takes place in a condenser, but a mere storage 
of chemical energy, which may afterward become 
electric. (See Cell, Storage.) 

Charging Leyden Jars toy Cascade. — (See 
Cascade ; Charging Leyde?i Jars fry.) 

Chart, Inclination —A map or chart 

on which the isoclinic lines are marked. (See 
Map or Chart, Inclination. Lines Isoclinic.) 



Cha.] 



94 



[Chr. 



Chart, Isodynamic A map or chart 

on which the isodynamic lines afe marked. 
(See Map or Chart, Isodynamic. Lines, 
Isodynamic.) 

Chart, Isogonal An isogonic chart. 

(See Map or Chart, Isogonal.) 

Chart, Isogonic ■ — A map or chart 

on which the isogonic lines are marked. (See 
Map or Chart, Isogonic. Lines, Isogonic?) 

Chatterton's Compound. — (See Com- 
pound, Chatterton's.) 

Chemical Change. — (See Change, Chem- 
ical?) 

Chemical Effect. — (See Effect, Chemical?) 

Chemical Equivalent. — (See Equivalent, 
Chemical?) 

Chemical Galvano-Cautery. — (See Cau- 
tery, Galvano-C hemic al?) 

Chemical Phosphorescence. — (See Phos- 
phorescence, Chemical?) 

Chemical Photometer.— (See Photometer, 
Chemical?) 

Chemical Potential Energy. — (See En- 
ergy, Che?nical Potential?) 

Chemical Recorder, Bain's (See 

Recorder, Chemical, Bains?) 

Chemistry, Electro That branch 

of electric science which treats of chemical 
compositions and decompositions effected by 
the electric current. (See Electrolysis. De- 
composition, Electrolytic?) 

That branch of chemistry which treats of 
combinations and decompositions by means 
of electricity. 

Electro-chemistry treats of the formation of 
new molecules, by the combination of atoms under 
the electric force, as well as the decomposition of 
molecules by electricity. 

The action of a series of sparks passed through 
air, in forming nitric acid, is an instance of the 
former, and electrolytic decompositions in gen- 
eral afford instances of the latter. 

Chimes, Electric —Bells rung by 

the attractions and repulsions of electrostatic 
charges. 

The bells B and B, Fig. 121, are conductively 
connected to the prime or positive conductor -f-, 



of a frictional machine. The bell C, is insulated 
from this conductor by means of a silk thread, 
but is connected with the ground by the metallic 
chain. Under these 
circumstances the 
clappers, 1, 1, insu- 
lated by silk threads, 
t, t, are attracted to 
B, B, by an induced 
charge and repelled 
to C, where they lose 
their charge only to 
be again attracted to 
B, B. In this way 
the bells will con- 
tinue ringing as long 
as the electric ma- 
chine is in operation. 

Choking Coil.— (See Coil, Choking?) 

Chronograph, Electric —An elec- 

trie apparatus for automatically measuring 
and registering small intervals of time. 

Chronographs, though of a variety of forms, 
generally register small intervals of time by 
causing a tuning fork or vibrating bar of steel, 
whose rate of motion is accurately known, to 
trace a sinuous line on a smoke-blackened sheet: 
of paper, placed on a cylinder driven at a uni- 
form rate of motion by clockwork. If the fork 
is known to produce, say, 256 vibrations per 
second be used, each sinuous line will represent 
•gig part of a second. 




Fig. 121 




Fig. 122, Electric Chronograph. 

An electro-magnet is used to make marks on 
the line at the beginning and the end of the 
observation, and thus permit its duration to be 
measured. 

In the form of electric chronograph shown 



Chr.] 



95 



[Cir. 



in Fig. 122, an electro-magnet, the armature of 
which carries a pen, is supported on a carriage 
moved by clockwork over a sheet of paper 
wrapped on a rotating cylinder. A clock is so 
connected with the circuit of the electro-magnet 
that it makes or breaks the circuit at the end of 
every second second, and so moves, or displaces, 
the armature, as to cause an elevation or depres- 
sion in the otherwise continuous sinuous line, that 
would be drawn on the paper by the double 
motion of its rotation and the movement of the 
pen-carriage. 

When it is desired to know with great precision 
the exact time of occurrence of any event, 
such, for example, as the transit of a star over the 
meridian, the observer, who carries in his hand a 
push button, or other form of electric key, closes 
or opens the circuit at the exact moment and so 
superposes an additional mark on the sinuous 
line. Since the exact time of starting the clock 
is known, and the intervals between the regular 
successive marks are two seconds each, it is easy to 
estimate from its position between any two such 
marks the exact value of the additional mark inter- 
posed. Fig. 122, taken from Young, shows a form 
of chronograph by Warner & Swasey. The de- 
tails of this apparatus will be understood from 
an inspection of the drawing. 

Chronograph Record. — (See Record, 
Chronograph?) 

Chronoscope, Electric An appa- 
ratus for electrically indicating, but not 
necessarily recording, small intervals of time. 

This term is often used for chronograph. 

The interval of time required for a rifle ball 
to pass between two points may be determined 
by causing the ball 1o pierce two wire screens 
placed a known distance apart. As the screens 
are successively pierced, an electric circuit is 
thus made or broken, and marks are registered 
electrically on any apparatus moving with a 
known velocity. 

Cigar-Lighter, Electric —(See 

Lighter, Cigar, Electric?) 

Cipher Code.— {See Code, Cipher) 

Circle, Azimuth — The arc of a 

great circle passing through the point of the 
heavens directly overhead, called the Zenith, 
and the point directly beneath, called the 
Nadir. 



Circle, Dipping — A term some- 
times applied to an inclination compass. (See 
Compass, Inclination.') 

Circle, Galvanic A term some- 
times used for galvanic circuit. (See Circuit, 
Galvanic.) 

Circle of Reference. — The circle, by refer- 
ence to which simple harmonic motion may 
be studied, by comparison with uniform mo- 
tion around such circuit. (See Motion, 
Simple Harmonic) 

Circle, Voltaic A name formerly 

employed for voltaic cell or circuit. (See 
Cell, Voltaic. Circuit, Voltaic) 

Circuit, Air-Magnetic That part 

of the path of a line of magnetic induction 
which takes place wholly through air. 

Circuit, Alternating Current A 

circuit in which an alternating current of 
electricity is flowing. (See Current, Alter- 
nating) 

Circuit, Astatic A circuit consist- 
ing of two closed curves enclosing equal sur- 
faces. 

Such a circuit is 
not deflected by the 
action of the earth's 
field. The circuit dis- 
posed, as shown in 
Fig. 123, is astatic and 
produces two equal 
and opposite fields at 
SandS'. (See Mag- 



A 

-1 



Astatic Circuit. 



Fig. 123. 
netisfti, Ampere's Theory of.) 

Circuit, Balanced-Metallic A me- 
tallic circuit, the two sides of which have 
similar electrical properties. 

Circuit Breaker. — (See Breaker, Circuit) 

Circuit, Broken An open circuit. 

A circuit, the electrical continuity of which 
has been disturbed, and through which the 
current has therefore ceased to pass. 

Circuit, Closed A circuit is closed, 

completed, or made when its conducting 
continuity is such that the current can pass. 

Circuit, Closed Iron-Magnetic 

The name applied to the path of any line 



Cir.] 



96 



[Cir. 



of magnetic force, which takes place entirely 
through iron, steel, or other paramagnetic sub- 
stance. 
Circuit, Closed-Loop Parallel A 

variety of parallel circuit in which the lead 
and the return circuit are arranged in the 
form of concentric circuits, with the recep- 
tive devices placed radially between them. 

Circuit, Closed-Magnetic A mag- 
netic circuit which lies wholly in iron or other 
substance of high magnetic permeability. 

All lines of magnetic, force form closed circuits. 
The term closed-magnetic circuit is used in con- 
tradistinction to a divided circuit, or one in which 
an air gap exists in the substance of high mag- 




Fig. 124. Closed-Magnetic Circuit. 

netic permeability forming the remainder of the 
circuit. This introduces so high a resistance that 
such a circuit is sometimes called an open -mag- 
netic circuit. An iron ring, such as shown in 
Fig. 124, forms a closed-magnetic circuit. 

Circuit, Closed-Magnetic, of Atom 

A closed-magnetic circuit, or closed lines 
of magnetic force supposed to lie entirely in 
the atom itself. 

The assumption of closed lines of magnetic 
force in atoms or molecules was made in order to 
explain the original polarity of the same, and to 
account for some of the other phenomena of 
magnetism. 

When the atom is subjected to a magnetizing 
force, such, for example, as the field of an electric 
current, these closed lines of force are assumed 
to open out and produce lines of polarized atoms. 
According to Lodge, for every single line of force 
produced by the current passing through a coil 
of wire surrounding an iron core, some 3,000 
lines of magnetic force are added to it from the 
iron. Therefore an iron core greatly increases 
the magnetic strength of a hollow coil of wire. 



Circuit, Closed-Magnetic, of Molecule 

— A closed-magnetic circuit assumed to lie 
wholly within the molecule. 

As it is not known whether the assumed mag- 
netic circuit lies within the atom or the molecule, 
it is called indifferently the closed-atomic or 
closed-molecular circuit. (See Circuity Closed- 
Magnetic, of At 0171.) 

Circuit, Completed —A closed 

circuit. 

A circuit, the conducting continuity of 
which is unbroken. 

A completed circuit is also called a made or 
closed circuit. 

Circuit, Compound A circuit con- 
taining more than a single source, or more 
than a single electro-receptive device, or both, 
connected by conducting wires. 

The term compound circuit is sometimes ap- 
plied to a series circuit. (See Circuit, Series.) 
The term, however, is a bad one, and is not 
generally adopted. 

Circuit, Constant-Current A cir- 
cuit in which the current or number of am- 
peres is maintained constant notwithstanding 
changes occurring in its resistance. 

The series-circuit, as maintained for arc-lamps, 
is a constant-current circuit. (See Regulation, 
Automatic.) 

Circuit, Constant-Potential — A 

circuit, the potential or number of volts of 
which is maintained approximately constant. 
The multiple-arc or parallel circuit is an ap- 
proximately constant-potential circuit. 

Circuit, Derivative A derived or 

shunt circuit. (See Circuit, Shunt) 
Circuit, Derived 

A term applied to a shunt 
circuit. 

If, in addition to the galva- 
nometer G, the conductor S, 
Fig. 125, be connected with 
the circuit of the battery B, a 
derived circuit will thus be 
established, and a current, will 
flow through S, diminishing 
the current in the galvanom- 
eter. (See Circuit, Shunt.) 




Fig. 125. Derived 
Circuit. 



Cii\] 



97 



[Cir. 



Circuit, Divided-Magnetic A 

magnetic circuit which lies partly in iron, or 
other substance, of high magnetic perme- 
ability, and partly in air. 

A divided-magnetic circuit is shown in Fig. 126. 




Fig. 126. Divided Magnetic Circuit. 

'Where the iron ring is separated by the air gap, 
a high magnetic resistance is introduced, owing 
to the fact that the iron is at these points replaced 
by air, whose magnetic reluctance is great 

Circuit, Double-Wire — A term 

sometimes used for a simple multiple circuit 
with two conductors or wires. (See Circuit, 
Multiple) 

The term double-wire circuit is used in contra- 
distinction to single-wire circuit. (See Circuit, 
Single- Wire. ) 

Circuit, Earth A circuit in which 

the ground or earth forms part of the con- 
ducting path. 

Circuit, Earth, Telegraphic — 

That portion of a telegraphic circuit which is 
completed through the earth or ground. 

Circuit, Electric —The path in 

which electricity circulates or passes from a 
given point, around or through a conducting 
path, back again to its starting point. 

All simple circuits consist of the following 
parts, viz.: 

(1.) Of an electric source which may be a 
voltaic battery, a thermopile, a dynamo-electric 
machine, or any other means for producing elec- 
tricity. 

(2.) Of leads or conductors for carrying the 
electricity out from the source, through whatever 
apparatus is placed in the line, and back again to 
the source. 

(3.) Various electro-receptive devices, such as 
electro-magnets, electrolytic baths, electric 
motors, electric heaters, etc., through which 



passes the current by which they are actuated or 
operated. 

Circuit, Electrostatic The circuit 

formed by lines of electrostatic force. 

Lines of electrostatic force, like lines of mag- 
netic force, form closed circuits. Hence the 
origin of the phrase electrostatic circuit. (See 
Force, Electrostatic, Lines of.) 

Circuit, External That part of a 

circuit which is external to, or outside the elec- 
tric source. 

The circuit external to the source consists of 
two distinct parts, viz. : 

(1.) The conductors or leads. 

(2 ) The electro-receptive or translating de- 
vices. 

It is in the external circuit only that useful 
work is done by the current. 

Circuit, Forked A term sometimes 

used in telegraphy for a number of circuits 
that radiate from a given central point. 

Circuit, Galvanic A term some- 
times employed instead of voltaic circuit. 

The term galvanic in place of voltaic is unwar- 
ranted by the facts of electric science. (See Cir- 
cuit, Voltaic. ) 

Galvani thought he had discovered the vital 
fluid or source of animal life. Volta first pointed 
out the true explanation of the phenomena ob- 
served in Galvani's frog, and devised means 
for producing electricity in this manner. The 
terms voltaic battery, cell, circuit, etc., are there- 
fore preferable. 

Circuit, Ground A circuit in which 

the ground forms part of the path through 
which the current passes. 

As the ground is not always a good conductor, 
the terminals should be connected with the gas or 
water pipes, or with metallic plates, called groimd 
plates. Such connection, or any similar ground 
connection, is usually termed the ground or earth. 

Circuit, Ground, Telegraphic 

An earth circuit used in any system of telegra- 
phy. (See Circuit, Earth, Telegraphic) 

Circuit, Grounded — A ground cir- 
cuit. 

Circuit, Incomplete An open or 

broken circuit. 



Cir.] 



98 



[Cir. 



A circuit whose conducting continuity is 
incomplete. 

Circuit, Inductive Any circuit in 

which induction takes place. 

Circuit, Internal That part of a 

circuit which is included within the electric 
source. 

The electric current passing through the inter- 
nal circuit does no useful work. 

Circuit, Leg of One part of a 

twisted or metallic circuit. 

Circuit, Line The wire or other 

conductors in the main line of any telegraphic 
or other electric circuit. 

Circuit, Line, Telegraphic The 

conductor or line connecting different tele- 
graphic stations. 

Circuit, Local-Battery The cir- 
cuit, in a telegraphic system, in which is 
placed a local battery as distinguished from a 
main battery. (See Telegraphy, American 
or Morse System of.) 

Circuit, Loop A term sometimes 

applied to a circuit in parallel or multiple-arc. 
(See Circuit, Multifile?) 

Circuit Loop Break. — (See Break, Circuit 
Loofi) 

Circuit, Made A completed circuit. 

A circuit, whose conducting continuity is 
unbroken. 

A made circuit is often called a completed or 
closed circuit. (See Circuit, Closed.) 

Circuit, Magnetic The path through 

which the lines of magnetic force pass. 
All lines of magnetic force form closed circuits. 




is often placed around the magnet. The magnet 
is then said to be iron-clad. 

The armature of a magnet lowers the magnetic 
resistance by affording a better path for the line s 
of magnetic force than the air between the 
poles. 

The magnetic circuit always tries to shorten its 
path, or to render itself as compact as possible. 
This is seen in the action of an armature drawn 
towards a magnet pole 

Circuit, Main-Battery — A term 

sometimes used for line circuit. (See Circuit, 
Line?) 

Circuit, Metallic A circuit in which 

the ground is not employed as any part of the 
path of the current, metallic conductors being 
employed throughout the entire circuit. 

Circuit, Multiple A compound cir- 
cuit, in which a number of separate sources 
or separate electro-receptive devices, or both, 
have all their positive poles connected to a 
single positive lead or conductor, and all their 
negative poles to a single negative lead or 
conductor. 

The connection of three Bunsen cells, in mul- 
tiple, is shown in Fig. 128, where the three car- 




Fig. 127. Magnetic Circuit. 

In the bar magnet, shown in Fig. 127, part of 
this path is through the air. In order to reduce 
or lower the resistance of a magnetic circuit, iron 



Fig. 128. Batteries connected in a Multiple Circuit. 

bons, C, C, C, are connected together so as to form 
the positive, or -\- terminal of the battery, and 
the three zincs, Zn, Zn, Zn, are similarly con- 
nected together so as to form the negative, or — 
terminal. 

The electromotive force is the same as that of 
a single cell, or source. The internal resistance 
of the source is as much less than the resistance of 
any single source as the area of the combined 
negative or positive plates is greater than that of 
any single negative or positive plate ; or, in other 
words, is less in proportion to the number of cells, 
or other separate sources so coupled. 

The connection of six cells in multiple or 
parallel circuit, is shown in Fig. 129. 



Cir.] 



99 



[Cir. 



In the case of the six cells, the current would 



be, 



+ r', 



where E, is the electromotive force, r, the in- 
iernal, and r', the external resistance. 




Fig. I2g. Six Cells Connected in Multiple. 

In the case of voltaic cells the effect of multiple 
connection on the internal resistance of the source 
is to increase the area of cross-section of the 
liquid in the direct proportion of the number of 
cells added, and consequently to decrease the re- 
sistance in the same proportion. 

When strong or large currents of low electro- 
motive force are required, connections in multi- 
ple-arc are generally employed. 

The multiple-arc connection was formerly 
called connedion-f or -quantity. This term is now 
abandoned. 

The total resistance for the parallel circuit is 
obtained as follows: calling the separate resist- 
ances of the separate electro-receptive devices, 
R', R", R'", etc., etc., etc., total resistance, 

p _ R'XR"X R'" 

R' R" -f- R" R'" + R' R'" 

or, what is the same thing, the conductivity is the 
sum of the reciprocal of the separate resistances, 
*'. e. : 



i i 

Conductivity = -rp- -j- Tp - 



R 



The joint resistance of only two separate resist- 
ances joined in a multiple-circuit is equal to the 
product of the separate resistances divided by 
their sum. 

When the separate resistances joined in multiple 
arc are all of the same value, the joint resistance is 
equal to the resistance of one of them divided by 
their number. 

Circuit, Multiple-Arc A term often 

used for multiple circuit. (See Circuit, Mul- 
tiple) 

Circuit, Multiple-Series -A com- 
pound circuit in which a number of separate 



sources, or separate electro-receptive devices, 
or both, are connected in a number of sepa- 
rate groups in series, and these separate 
groups subsequently connected in multiple. 
In Fig. 130, a multiple-series circuit of six 
c 



J 



Fig. 130. Multiple-Series-Connected Cells. 

sources is shown, in which three separate groups 
of two series-connected cells are coupled in multi- 
ple. The current takes the paths indicated by the 
arrows. The electromotive force of the source 
will be increased in proportion to the number of 
cells in series, and the internal resistance de- 
creased in proportion to the number in parallel. 



Fig. 1 J 1. Cells Connected in Multiple- Series . 






+ r' 



In Fig. 131, six cells are arranged in two 
groups of three series-connected cells, and these 
three groups connected in parallel. 

Calling r, the resistance of each separate cell, 
the total resistance for the multiple-series circuit 
for a circuit containing three cells in parallel and 
two in series is, 



for three in series and two in parallel, 

R=_3L_. 
2 

If, therefore, the circuit of this battery be 

closed by a resistance equal to r, the current 

would be in the case of Fig. 130, 

2E 



Cir. 



100 



[Cir. 



Circuit, Negative Side of —The side 

of a circuit opposite to the positive side. 
(See Circuity Positive Side of.) 

That side or half of a circuit connected to or 
leading from the positive terminal of the source of 
current. 

Circuit, Open A broken circuit. 

A circuit, the conducting continuity of 
which is broken. 

Circuit, Open-Iron Magnetic — 

The path of a line of magnetic induction, 
which passes partly through iron, and partly 
through an air space. 

The magnetic circuit is always closed, that is 
the lines of magnetic force always form closed 
paths. The term " open " is used in contradis- 
tinction only to "closed " iron magnetic circuit, 
in which the entire path of a line of force passes 
through iron. (See Circuit, Magnetic.) 

Circuit, Parallel A name some- 
times applied to circuits connected in mul- 
tiple. (See Circuity Multiple?) 

Circuit, Parallel-Tree A form of 

parallel circuit in which the receptive devices 
are placed in parallel between the leads and 
returns, and the branches and sub-branches 
arranged in a tree-like form. 

Circuit, Positive Side of That side 

of a circuit, bent in the form of a circle, in 
which, if an observer stood with his head in 
the positive region, he would see the current 
pass round him from his right hand towards 
his left. — (Darnell.) 

Circuit, Recoil A term sometimes 

applied to the circuit that lies in the alterna- 
tive path of a discharge. (See Path, Alter- 
native?) 

Circuit, Return That part of a 

circuit by which the electric current returns to 
the source. 

In a multiple-circuit the lead that is con- 
nected to the negative terminals of the 
separate sources. 

Circuit, Series A compound cir- 
cuit in which the separate sources, or the sep- 
arate electro-receptive devices, or both, are so 
placed that the current produced in each, or 
passed through each, passes successively 



through the entire circuit from the first to the 
last. 

The six cells, shown in Fig. 132, are connected 
in series by joining the positive pole of each cell 
with the negative pole of the succeeding cell, the 
negative and positive poles at the extreme ends 




Fig. ^S 2 ' Series Circuit. 

being connected by conductors with the external 
circuit. 

The connection of three Leclanche cells in 
series is clearly shown in Fig. 133. The carbons,. 

z „ C+_ C4- . _-*- 




Pig, rS3' Voltaic Cells Connected in Series. 
C, C, of the first and second cells are connected to 
the zincs, Zn, Zn, of the second and third cells, 
thus leaving the zinc, Zn, of the first cell, and the 
carbon, C, of the third cell, as the terminals of 
the battery. The direction of the current is 
shown by the arrows. 

The resistance of such a connection is equal to 
the sum of the resistances of all of the separate 
sources. 

The electromotive force is equal to the sum of" 
the separate electromotive forces. 

If the electromotive force of a single cell is 
equal to E, its internal resistance to r, and the 
resistance of the leads and electro -receptive de- 
vices to r', then the current in the circuit, 

If six of such cells are coupled in series, the cur- 
rent becomes 

6E 



6r + r' 
If, however, the internal resistance of each cell be 
so small as to be neglected, the formula becomes 
6E, 
r' 



C = 



Cir.] 



101 



[Cir. 



or the current is six times as great as with one 
cell. 

The total resistance of the separate sources or 
electro-receptive "devices of the series circuit is 
* as follows, calling R', R", R'", etc., the separate 
resistance and R, the total resistance, 
■ R = R' + R" + R '", etc. 

The series connection of battery cells is used 
on telegraph lines, where a high electromotive 
force is required in order to overcome a consider- 
able resistance in the circuit, or in similar cases 
where the resistance in the external circuit is 
great, on account of a number of electro receptive 
devices being connected to the line in series. 

The series connection was formerly called 
connection for intensity. The term is now aban- 
doned. 

Circuit, Series-Multiple A com- 
pound circuit, in which a number of separate 
sources, or separate electro-receptive devices, 
or both, are connected in a number of sepa- 
rate groups in multiple-arc, and these sepa- 
rate groups subsequently connected in series. 

In the series multiple circuit the resistance of 
each multiple group is equal to the resistance of 
a single branch divided by the number of branches. 

If, for example, r, is the resistance of each sepa- 
rate branch of say seven parallel circuits in each 
of the separate groups of multiple circuits, then 
the resistance, R, of each separate multiple 
group is — 

R = _L. 
7 
The total resistance of the series-multiple cir- 
cuit is equal to the sum of the resistances of the 
separate multiple groups. The total resistance of 
the three groups is — 



r i r — 3*" 

7 7 7 ' 



An example of the series-multiple circuit is 
shown in Fig. 134, which is the method adopted 



Fig. 134. Series-Multiple Circuit. 
in the use of distribution boxes. Here a number 
of multiple groups or circuits are connected with 
each other in series, as shown. (See Box, Dis- 
tribution, for Arc Light Circuits. ) 

Circuit, Short A shunt, or by-path. 



of comparatively small resistance, around the 
poles of an electric source, or around any 
portion of a circuit, by which so much of the 
current passes through the new path, as vir- 
tually to cut out the part of the circuit around 
which it is placed, and so prevent it from re- 
ceiving an appreciable current.' 

Circuit, Shunt A branch or addi- 
tional circuit provided at any part of a cir- 
cuit, through which the current branches or 
divides, part flowing" through the original cir- 
cuit, and part through the new branch. 

A shunt circuit is in multiple circuit with the 
circuit it shunts. 

In the case of branch circuits each of the cir- 
cuits acts as a shunt to the others. Any number 
of additional or shunt circuits may be thus pro- 
vided. (See Laws, Kirch/toffs.) 

Circuit, Simple A circuit containing 

a single electric source, and a single electro- 
receptive device, connected by a conductor. 

The term simple circuit is sometimes applied 
to a multiple circuit. The term is not, however, 
a good one, and is not in general use. 

Circuit, Single- Wire A term some- 
times used for a grounded circuit. (See 
Circuit, Grounded?) 

The single-wire circuit is sometimes used m the 
distribution of incandescent lamps in multiple-arc. 
One pole of the dynamo is put to ground, and the 
other pole to a single wire or lead. The electro- 
receptive devices have one of their poles con- 
nected to th.s lead and the other pole to earth. 
The single-wire circuit is a very objectionable 
circuit so far as safety is concerned. 

It is frequently used, however, in the wiring of 
ships. 

Circuit, Through A telephonic or 

telegraphic circuit that has been completed 
through to a given station by cutting out inter- 
ruptions or breaks in the line by the connec- 
tion together of sections of different wires. 

Circuit, Time-Constant of —The 

time in which a current due to a constant 
electromotive force will rise in a conductor 
to a definite fraction of its maximum value. 

The ratio of the inductance of a circuit ta 
its resistance. 



€ir.] 



102 



[Cle. 



The time required from the moment of 
closing the circuit, for a current to rise to 

a value equal to e l of the full value, or 
e 

.632 of the maximum value. 

In the above, e, equals 2.71828, or the base of 
the Napierian system of logarithms. 

The time-constant is proportional to the con- 
ductivity of the circuit and its formal resistance. 

Approximately the time constant of a circuit is 
the time from closing the circuit, in which the 
current rises to two-thirds of its maximum value, 
this maximum value being determined by the 

formula, C = — . 
R 

The time -constant of a circuit may be reduced — 

(1.) By decreasing the self-induction of the cir- 
cuit. 

(2.) By increasing the resistance. 

In the case of a magnetic conductor the time- 
constant is proportional to a quantity (the perme- 
ability) which is determined by the capacity of 
the conductor to utilize part of the energy in 
producing magnetization of its substance. — {Flem- 
ing.) 

Circuit, Yoltaic The path through 

which the current flows out from a voltaic cell 
or battery, through the translating devices 
and back again to the cell or battery. 

Circuits, Forked —A term employed 

in telegraphy to indicate circuits that radiate 
from any single point. 

Forked circuits are employed in simultaneously 
transmitting messages to several stations. 

Circuits, Yarieties of Conducting 

paths provided for the passage of an electric 
current. 

Electric circuits may be divided, according to 
their complexity, into — 

(1.) Simple. 

(2.) Compound. 

According to the peculiarities of their connec- 
tions, into — 

(1.) Shunt or derived. 

(2.) Series. 

(3.) Multiple, multiple-arc or parallel. 

(4.) Multiple-series. 

(5.) Series-multiple. 

Either the circuits, the sources, or the electro- 



receptive devices may be connected in series, in 
multiple, in multiple-series or in series-multiple. 

According to their resistance, circuits are 
divided into — 

(1.) High-resistance. 

(2.) Low -resistance. 

According to their relation to the electric 
source, into — 

(1.) Internal circuits. 

(2.) External circuits. 

According to their position, or the work done, 
circuits are divided into very numerous classes; 
thus, in telegraphy, we have the following, viz.: 

(1.) The line-circuit. 

(2.) The earth or ground circuit. 

(3.) The local-battery circuit. 

(4.) The main -battery circuit, etc. 

Circular Bell.— (See Bell, Circular?) 
Circular Units.— (See Units, Circular?) 

Circular Units (Cross-Sections), Table 

of (See Units, Circular (Cross- Sec- 
tions), Table of.) 

Clamp, Carbon A carbon clutch. 

(See Clutch, Carbon, of Arc Lamp?) 

Clamp for Arc Lamps.— A clamp for 
gripping the lamp-rod, /*. e., the rod that sup- 
ports the carbon electrodes of arc lamps. 
(See Lamp, Electric, Arc.) 

Clamp, Rod A carbon clutch. (See 

Cla?np for Arc Lamps?) 

Clark's Compound. — (See Compound, 
Clark's?) 

Clark's Standard Voltaic Cell. — (See 
Cell, Voltaic, Standard, Clark's?) 

Clark's Standard Voltaic Cell, Ray- 

leigh's Form of (See Cell, Voltaic, 

Standard, RayleigJis Form of Clark's.) 

Clay Electrode.— (See Electrode, Clay?) 

Cleansing", Fire The removal of 

grease from metallic articles, that are to be 
electro-plated, by subjecting them to the action 
of heat. 

This cleansing is for the purpose of obtaining a 
uniform, adherent coating. 

Clearance-Space. — (See Stiace. Clearance) 



Cle.] 



103 



[CIo. 



Clearing-Out Drops.— (See Drops, Clear- 
ing-Out?) 

Cleat, Crossing 1 A cleat so arranged 

as to permit the crossing- of one pair of wires 
under or over another pair without contact 
with each other. 

Cleat- Wiring".— (See Wiring, Cleat.) 

Cleats, Electric Suitably shaped 

pieces of wood, porcelain, hard rubber or 
other non-conducting material used for fasten- 
ing and supporting electric conductors to 
-ceilings, walls, etc. 

A simple form of wooden cleat is shown in 
Fig. 135- 




Fig. 135. Wooden Cleat. 



Clepsydra, Electric 



-An instrument 



for measuring time by the escape of water or 
other liquid under electrical control. 

Climbers, Pole 

—Devices employed by 
linemen for climbing 
wooden telegraph poles. 

A climber with straps 
for attachment to the leg 
and foot is shown in Fig. 
136. 

Clip, Cable A 

term sometimes used for 
cable hanger. (See 
Hanger, Cable?) 

Clock, Electric 

— A clock, the works of 
which are moved, con- 
trolled, regulated or 
wound, either entirely or partially, by the elec 
trie current. 




Fig. 136. Climber and 
Straps. 



Electric clocks may be divided into three 
classes, viz.: 

(1.) Those in which the works are moved en- 
tirely or partially by the electric current. 

(2.) Those which are controlled or regulated 
by the electric current. 




Fig. 1 37. Controlling 
Clock. 



(3.) Those which are merely wound by the 
current. 

A clock moving independently of electric power 
is prevented from gain- 
ing or losing time, by 
means of a slight re- 
tardation or acceleration 
electrically imparted . 
The entire motion of 
the balance wheel is, 
sometimes imparted by 
electricity. 

An example of one oi 
many forms of controll- 
ing electric clocks is 
shown in Fig. 137, 
where the split battery 
(See Battery, Split), P 
N, is connected, as 
shown, to the spring 
contacts S and S'. In this way currents are sent 
into the circuit in alternately opposite directions. 

The pendulum bob, Fig. 138, of the con- 
trolled clock is formed of a hollow coil of insu- 
lated wire, which encircles one or both of two 
permanent magnets, A and A', placed with their 
opposite poles facing each other. 

When the pendulum of the controlling clock is 
in the position shown in Fig. 137, the current 
passes in the direction E P Sn W, etc., and through 
the coil C, Fig. 138. When the pendulum of the 
controlling clock is in con- 
tact with S', the current 
flows through Wn S' N E, 
etc., and through the coil 
C in the opposite direc- 
tion. In this manner a 
slight motion forwards or 
backwards is imparted to 
the pendulum, which is 
thus kept in time with the 
controlling clock. 

Mercury contacts are 
sometimes employed in 
place of the springs S and •£/ 
S'. Induction currents may f^\ 
also be employed. 

Clocks of non-electric ac- 
tion may be electrically 
controlled, or correctly set at certain intervals, 
either automatically by a central clock, or by the 
depression of a key operated by hand from an 
astronomical observatory. 




Fig. 138. Controlled 
Clock. 



Clo.] 



104 



[Clo. 



In a system of time-telegraphy , the controlling 
clock is called the master clock, arid the con- 
trolled clocks, the secondary clocks. 

Secondary clocks are generally mere dials, QOn- 




Fig. T£Q. Mechanism of Secondary Clock. 

taining step-by-step movements, for moving the 
hour, minute and second hands, as shown in 
Fig. 139- 

In Spellier's clock, a series of armatures H, 
Fig. 140, mounted on the circumference of a 




Fig. 140. Spellier's Electric Clock. 

wheel, connected with the escapement wheel, 
pass successively, with a step-by -step movement, 
over the poles of electro-magnets. On the com- 
pletion of the circuit, they are attracted towards 
the magnet, and on the breaking of the circuit 
they are drawn away by the fall of the weight F, 
placed on the lever D, pivoted at E. A pulley at 
E, runs over the surface of a peculiarly shaped 
cog on the escapement wheel. 

Clock, Electric Annunciator A 

clock, the hands or works of which, at cer- 
tain predetermined times, make electric con- 
tacts and thus ring bells, release drops, trace 
records, etc. 



Clock, Electrical-Controlling — ■ In 

a system of time telegraphy, the master clock, 
whose impulses move or regulate the second- 
ary clocks. (See Clock, Electric?) 

Clock, Electrically-Controlled In 

a system of time telegraphy, a secondary 
clock, that is either driven or controlled by 
the master clock. (See Clock, Electric?) 

Clock, Electrolytic, Tesla's A time 

piece in which the rotation of the wheel work 
is obtained by the difference in weight of the 
two halves of a delicately pivoted and well- 
balanced wheel placed in an electrolytic 
bath. 

In the electrolytic clock of Nikola Tesla, a deli- 
cately formed and balanced disc of copper is sup- 
ported on a horizontal axis at right angles to the 
shortest distance between the two electrode-, and 
placed in a bath of copper sulphate. Its two 
halves become respectively electro-positive and 
electro-negative when a current is passed through 
the bath, and consequently metal is deposited on 
one half and dissolved from the other half. The 
rotation of the disc under the influence of gravity 
is caused to mark time. 

An electrolytic clock could therefore be made 
to answer roughly as an electric meter. 

Clock, Master The central or con- 
trolling clock in a system of electric time-dis- 
tribution, from which the time is transmitted 
to the secondary clocks in the circuit. (See 
Clock, Electric?) 

Clock, Secondary Any clock in a 

system of time telegraphy that is controlled 
by the master clock. (See Clock, Electric) 

Clock, Self- Winding- A clock that 

at regular intervals is automatically wound by 
the action of a small electro-magnetic motor 
contained within it. 

This motor is usually run by one or more vol- 
taic cells, concealed in the case of the clock. 

Closed-Circuit. — (See Circuit, Closed?) 

Closed-Circuit Battery. — (See Battery, 
Closed- Circuit?) 

Closed-Circuit, Single-Current, Signal- 
ing (See Signaling, Single-Current, 

Closed- Circuity 



Clo.] 



105 



[Coe. 



Closed-Circuit Thermostat— (See Ther- 
mostat, Closed-Circuit?) 

Closed-Circuit Yoltaic Cell— (See Cell, 
Voltaic, Closed-Circuit?) 

Closed-Circuit Voltmeter. — (See Volt- 
meter, Closed-Circuit.) 

Closed-Circuited. — Placed in a closed or 
completed circuit. 

A voltaic battery, or other source, is closed- cir- 
cuited when its poles or terminals are electrically 
connected with each other. 

Closed-Circuited Couductor.— (See Con- 
ductor, Closed-Circuited.) 

Closed-Circular Current. — (See Current, 
Closed- Circular.) 

Closed-Coil Disc Dynamo-Electric Ma- 
chine. — (See Machine, Dy7iamo-Electric, 
Closed-Coil Disc?) 

Closed-Coil Drum Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric, 
Closed-Coil Drum?) 

Closed-Coil Dynamo-Electric Machine.— 
(See Machine, Dyjiamo-Electric, Closed- 
Coil.) 

Closed-Coil Ring Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric, 
Closed-Coil Ring?) 

Closed-Iron-Circuit Transformer.— (See 
Transformer, Closed-Iron-Circuit .) 

Closed-Loop Parallel- Circuit.— (See Cir- 
cuit, Closed-Loop Parallel?) 

Closed-Magnetic Circuit.— (See Circuit, 

Closed-Magnetic.) 

Closed-Magnetic Core. — (See Core, Closed- 
Magnetic?) 

Closure. — The completion of an electric 
circuit. 

Cloth Discs, Carbonized, for High Re- 
sistances Discs of cloth carbonized by 

heating to an exceedingly high temperature 
in a vacuum, or out of contact with air. 

After carbonization the discs retain their flex- 
ibility and elasticity and serve admirably for high 
resistances. When piled together and placed in 
glass tubes, they form excellent variable resist- 
ances when subjected to varying pressure. 



Club-Footed Magnet. — (See Magnet, 
Club-Footed?) 
Clutch, Carbon, of Arc Lamp A 

clutch or clamp attached to the rod or other 
support of the carbon of an arc lamp, pro- 
vided for gripping or holding the carbon. 
(See Lamp, Electric Arc.) 

Clutch Rod.— (See Rod, Clutch.) 

Coating, Metallic — A covering or 

coating of metal, usually deposited from 
solutions of metallic salts by the action of an 
electric current . (See Plating, Electro?) 

Coating of Condenser.— A sheet of tin 
foil on one side of a Leyden jar or condenser, 
directly opposite a similar sheet on the other 
side for the purpose of receiving and collecting 
the opposite charges. (See Jar, Leyden. 
Condenser?) 

Coatings of Leyden Jar.— The sheets of 
tin foil or other conductor on the opposite 
sides of a Leyden jar or condenser. (See 
Jar, Leyden. Condenser?) 

Code, Cipher A code in which a 

number of words or phrases are represented 
by single words, or by arbitrary words or syl- 
lables. 

The message thus received requires the posses- 
sion of the key to render it intelligible. 

Code,Telegraphic The pre-arranged 

signals of any system of telegraphy. (See 
Alphabet, Telegraphic. Alphabet, Tele- 
graphic, Morse's. Alphabet, Telegraphic, 
International Code?) 

Co-efficient, Algebraic A number 

prefixed to any quantity to indicate how 
many times that quantity is to be taken. 

The number 3, in the expression 3a, is a co- 
efficient and indicates that the a, is to be taken 
three times, as a -j- a -f- a = 3a. 

Co-efficient, Economic, of a Dynamo- 
Electric Machine The ratio between 

the electrical energy, or the electrical horse- 
power of the current produced by a dynamo, 
and the mechanical horse-power expended in 
driving the dynamo. 

The economic co -efficient is usually called the 
efficiency. 



Coe.] 



106 



[Coi. 



The efficiency may be the commercial effi- 
ciency, which is the useful or available energy in 
the external circuit divided by the total mechan- 
ical energy; or it may be the electrical efficiency, 
which is the available electrical energy divided 
by the total electrical energy. 

The efficiency of conversion is the total elec- 
trical energy developed, divided by the total 
mechanical energy applied. 

If M, equals the mechanical energy, 
W, the useful or available electrical energy, 

and 
w, the electrical energy absorbed by the 

machine, and 
m, the stray power, or the power lost in 
friction, eddy currents, air friction, etc. 
Then, since 

M = W-fw + m, 
The Commercial Efficiency 
W_ W 

"M ~~ W + w -f m" 
The Electrical Efficiency 
W 
W + w' 
The Efficiency of Conversion 

_W + w_ W-fw 



M 



W 



w -f-m 

Co-efficient of Electro-Magnetic Inertia. 

— (See Inertia, Electro-Magnetic, Co-effi- 
cient of.) 

Co-efficient of Expansion. — (See Expan- 
sion, Co-efficient of.) 

Co-efficient of Expansion, Linear 

(See Expansion, Linear, Co-efficient of) 

Co-efficient of Magnetic Induction. — (See 
Induction, Magnetic, Co-efficient of) 

Co-efficient of Magnetization. — (See 
Magnetization, Co-efficient of.) 

Co-efficient of Mutual- Inductance. — (See 
Inductance, Mutual, Co-efficient of) 

Co-efficient of Mutual-Induction. — (See 
Induction, Mutual, Co-efficient of) 

Co-efficient of Self-induction. — (See In- 
duction, Self, Co-efficient of) 

Coercitive Force. — (See Force, Coerci- 
tive) 

Coerciye Force. — (See Force, Coercive) 

Coil, Choking A coil of wire so 




Fig. 141. Choking- 
Coil. 



wound on a core of iron as to possess high- 
self-induction. 

Choking-coils are used to obstruct or cut off an 
alternating current with a loss of power less thart 
with the use of a mere ohmic resistance. 

Fig. 141 shows a choking-coil. It consists of 
a circular solenoid of insulated wire, wound 
on a core of soft iron wire. A thorough divis- 
ion of the core is obtained by forming it of coils 
of insulated iron wire. In this way, no eddy 
currents are produced in the coil. When a simple 
periodic electromotive force is applied to the 
terminals of such a coil, if 
the magnetic permeability 
of the coil is constant, a 
simple periodic current is 
produced, which lags be- 
hind the phase of the im- 
pressed electromotive force 
by a constant angle. If 
the impressed electromo- 
tive force is sufficiently great to more than satu- 
rate the core, the choking coil ceases to choke 
the current. The higher the periodicity the 
greater is the choking effect of a given coil, or the 
smaller the coil may be made to produce a given 
effect. 

Since an open-magnetic circuit requires a 
greater current to saturate it than a closed -mag- 
netic circuit, the complete throttling or choking 
power of such a coil is increased by forming its 
core of a closed magnetic circuit, i. e., of a circuit 
in which there is no air space or gap. (See Circuit, 
Divided- Magnetic. Circuit, Closed- Magnetic) 

Coil, Electric A convolution of in- 
sulated wire through which an electric current 
may be passed. (See Magnet, Electro) 

The term coil is usually applied to a number 
of turns or to a spool of wire. 

Coil, Impedance A term sometimes 

applied to a choking-coil. (See Coil, Chok- 
ing) 

Such a coil has a high self-induction. Its im- 
pedance is therefore high. (See Induction, Self* 
Impedance) 



Coil, Induction 



-An apparatus con- 



sisting of two parallel coils of insulated wire 
employed for the production of currents by 
mutual induction. (See Induction, Mutual 
Induction, Electro-Dynamic) 



Coi.] 



107 



[Coi. 



A rapidly interrupted battery current, sent 
through a coil of wire called the primary coil, 
induces alternating currents in a coil of wire called 
the secondary coil-. 

As heretofore made, the primary coil consists of 
a few turns of a thick wire, and the secondary 
coil of many turns, often thousands, of fine wire. 
Such coils are generally called Ruhmkorff coils, 
from the name of a celebrated manufacturer of 
them. 

In the form of Ruhmkorff coil, shown in Fig. 
142, the primary wire, wound on a core formed 




Fig 142. Ruhmkorff Coil. 

of a bundle of soft iron wires, has its ends brought 
out as shown at f, f. The fine wire, forming the 
secondary coil, is wrapped around an insulated 
cylinder of vulcanite, or glass, surrounding the 
primary coil. This wire is very thin, and in some 
coils is over one hundred miles in length. 

If the core of an induction coil were made solid 
it would heat considerably and therefore cause a 
loss of energy. The core is therefore laminated, 
usually by forming it of a bundle of soft iron wire. 

Too great a division of the core, however, is 
inadvisable, since, although the eddy currents 
therein are thereby avoided, yet, too great a 
division of the core acts practically so to 
decrease the magnetic permeability that the 
greatest efficiency cannot be obtained. 

The ends of the secondary coil are connected 
to the insulated pillars A and B. 

The primary current is rapidly broken by 
means of a mercury break, shown at L and M. 

The commutator, shown to the right and front 
of the base, is provided for the purpose of cutting 
off the current through the primary, or for chang- 
ing its direction. When a battery which produces 
a comparatively large current of but a few volts 
electromotive force is connected with the pri- 
mary, and its current rapidly interrupted, a 
torrent of sparks will pass between A and B, 
having an electromotive force of many thousands 
of times the number of volts of the primary cur- 



rent, but of a correspondingly smaller current 
strength. 

In such cases, excepting losses during conver- 
sion, the energy in the primary current, or C E, 
is equal to the energy in the secondary current, 
or C E'. As much therefore as E', the electro- 
motive force of the secondary current, exceeds E, 
the electromotive force of the primary current, 
the current strength C, of the secondary, will be 
less than the current strength C, of the primary. 
This is approximately true only, and only in in- 
duction coils possessing a closed magnetic circuit. 
(See Transformer .) 

Fig. 143 shows diagramatically the arrange- 

S/ SI 



Hltllll'llPlllllllllllll 


illvUe. 




CR= 


b 


€ —a 


— - •■ 




Fig. 143. Circuit Connections 0/ Induction Coil. 

ment and connection of the different parts of an 
induction coil. 

The core IF, consists of a bundle of soft iron 
wires, each of which is covered with a thin insu- 
lating layer of varnish or oxide. A primary wire 
P P, consisting of a few turns of comparatively 
thick wire, is wound around the core, and a 
greater length of thin wire S S, is wound upon the 
primary. This is called the secondary. So as 
not to confuse the details of the figure it is repre- 
sented as a few turns. 

The terminals of the battery B, are connected 
to the primary wire, through the automatic inter- 
rupter, in the manner shown. It will be seen that 
the attraction of the core II', for the vibrating 
armature H, will break contact at the point o, and 
cause a continued interruption of the battery 
current. 

The condenser cc', is connected as shown. It 
acts to diminish the sparking at the contact points 
on breaking contact, and thus, by making the 
battery current more sudden, to make its in- 
ductive action greater. 

The reactions which take place when a simple 



Coi.] 



108 



[Coi. 



periodic electromotive force is impressed on the 
primary of an induction coil are substantially 
thus stated by J. A. Fleming : 

(i.) The application of a simple periodic im- 
pressed electromotive force produces a simple 
periodic current, moving under an effective elec- 
tromotive force of self-induction, and brings into 
existence a counter- electromotive force of self- 
induction, which causes the primary current to 
lag behind, by an angle called the angle of lag. 

(2.) The field around the primary, and, there- 
fore, the induction through the secondary, is in 
consonance with the primary current, and the im- 
pressed electromotive force in the secondary is 
in quadrature with the primary current. (See 
Consonance. Quadrature, In.) 

(3.) The secondary-impressed electromotive 
force gives rise to a secondary current moving 
under an effective electromotive force and creat- 
ing a counter electromotive force of self-induc- 
tion. 

(4.) This secondary current reacts in its turn 
on the primary, and creates what is called the 
back -electromotive force, or the reacting-induc- 
tive-electromotive force of the primary circuit. 

(5.) There is then a phase-difference between 
the primary and secondary currents, and also be- 
tween the primary-impressed electromotive force 
and the primary current. 

If, as in Fig. 144, two electric circuits are 




ECONDARY 
CIRCUIT 



Fig. 144. Electric and Magnetic Link. 

linked with a magnetic circuit, and a small 
periodic electromotive force be impressed on the 
primary, the following phenomena occur: 

(1.) A periodic primary current is set up in 
the primary circuit, which, though of the same 
periodic time as the impressed electromotive 
force, differs from it in phase. 

(2.) A wave of counter electromotive force is 
produced in the primary circuit by the inductive 
action, which does not coincide either with the 
impressed electromotive force, nor with the 
primary current. 

(3.) A wave of magnetization is produced in 
the iron core, which lags behind the primary 



current by somewhat less than 90 degrees of 
phase. 

(4.) A wave of impressed electromotive force 
is produced in the secondary circuit, due to and 
measured by the rate of change of magnetic in- 
duction in the core, and lagging 90 degrees, or 
more, behind the magnetization wave. 

'(5.) A wave of secondary current, lagging be- 
hind the secondary electromotive force in phase, 
except where the circuit consists of a few turns of 
conductor, or is connected with an external cir- 
cuit of practically no inductance. — {Fleming.) 

Coil, Induction, Inverted — An 

induction coil in which the primary coil is 
made of a long, thin wire, and the secondary 
coil of a short, thick wire. 

By the use of an inverted coil, a current of high 
electromotive force and comparatively small cur- 
rent strength, i. e., but of few amperes, is con- 
verted or transformed into a current of compar- 
atively small electromotive force and large cur- 
rent strength. For advantages of this conversion 
see Electricity, Distribution of, by Alternating 
Currents. 

Inverted induction coils are called converters or 
transformers. (See Transformer.) 

Coil, Induction, Medical —An 

induction coil used for medical purposes, 

A form of induction coil used for medical pur- 
poses is shown in Fig. 145. 




Fig. 145. Medical Induction Coil. 

Coil, Induction, Microphone An 

induction coil, in which the variations in the 
circuit of the primary are obtained by means 
of microphone contacts. (See Microphone) 

The carbon-button telephone transmitter is a 
microphone in its action, its electric resistance 
varying with the varying pressure caused by the 
sound waves. * The carbon-button is in the prim- 
ary circuit of an induction coil, variations in 



Coi.] 



109 



[Coi, 



primary of which, under the influence of the 
sound waves, produce corresponding variations 
in the currents induced in the secondary. 

Coil, Kicking A term sometimes 

applied to a Choking-Coil. (See Coil, Chok- 
ing) 

The term kicking-coil has arisen from the fact 
that the impedance due to self-induction opposes 
the starting or stopping of the current somewhat 
in the manner of an opposing kick. 



Coil, Mag-net 



— A coil of insulated 



wire surrounding the core of an electro-mag- 
net, and through which the magnetizing cur- 
rent is passed. (See Magnet., Electro) 

Coil, Primary That coil or con- 
ductor of an induction coil or transformer, 
through which the rapidly interrupted or alter- 
nate inducing currents are sent. 

In the Ruhmkorff induction coil the primary 
coil consists of a comparatively short length of 
thick wire, the secondary coil being formed of 
a comparatively great length of fine wire. In 
the transformer or converter, the primary coil 
consists of wire that is longer and thinner than 
that in the secondary coil. In other words, the 
transformer or converter consists of an inverted 
induction coil. (See Coil, Induction. Trans- 
former.) 

Coil, Reaction A magnetizing coil, 

surrounded by a conducting covering or 
sheathing, which opposes the passage of 
rapidly alternating currents less when directly 
over the magnetizing coil than when a short 
distance from it. 

A term often used for choking-coil. (See 
Coil, Choking.) 

Coil, Reaction, Balanced A coil 

employed in a 
system of distri- 
bution by means 
of transformers 
for maintaining 
a constant cur- 
rent in the sec- 
ondary circuit, Fig- 146. Balanced- Reaction Coil. 

despite changes in the load placed therein. 
A balanced-reaction coil is shown in Fig. 146. 




A reaction coil is placed in the circuit of lamps in 
series in a constant potential system. The sheath- 
ing of this coil is maintained in a balanced position 
by the counter weight P, and the spring S. If now 
a lamp is extinguished in the circuit, the increase 
of current, due to decreased resistance, causes the 
sheath to be deflected, and, thus increasing the 
self-induction of the coil, reduces the lamp current 
to its normal value. 

Coil, Resistance A coil of wire 

of known electrical resistance employed for 
measuring resistance. 

In order to avoid self-induction and the mag- 
netizing effects of the coils on the needles of the 
galvanometer used in electric measurements, as 
well as the disturbing effects of self-induction, the 
wire of the resistance coil is doubled on itseli 
before being wound, and its ends connected 
with the brass bars, E, E, Fig. 147. The inser- 




Fig. 147. Connections of Resistance Coils. 

tion of the plug-key cuts the coil out of the cir- 
cuit by short-circuiting. (See Box, Resistance. 
Bridge, Electric. Coil, Resistance, Standard.) 
The coils are made of German silver, or plati 
noid, the resistance of which is not much 
affected by heat. 

Coil, Resistance, Standard A coil 

the resistance of which is that of the stand- 
ard ohm or some multiple or sub-multiple 
thereof. 

The standard ohm, as issued by the Electric 
Standards Committee of England, has the form 
shown in Fig. 148. The coil of wire is formed of 
an alloy of platinum and silver, insulated by silk 
covering and melted paraffine. Its ends are sol- 
dered to thick copper rods, r, r'. for ready con- 
nection with mercury cups. The coil is at B. 
The space above it, at A, is filled with paraffine. 
A hole, at t, runs through the coil for the readv 



CoL] 



110 



[Coi. 



insertion of a thermometer. The lower part of 
the coil, B, is immersed in water up to the shoul- 
der of A, and the water stirred from time to 




Fig. 148. Standard Ohm. 

time. Since the coil is heated by the current, suc- 
cessive observations should be at least ten minutes 
apart. Only mild currents should be passed 
through the coils. 

Coil, Resistance, Standardized 

Resistance coils whose resistances have been 
carefully determined by comparison with a 
standard ohm or other standard coils. 

Coil, Ruhmkorff A term some- 
times applied to any induction coil, the 
secondary of which gives currents of higher 
electromotive force than the primary. (See 
Coil, Induction?) 

Coil, Secondary That coil or con- 
ductor of an induction coil or transformer, 
in which alternating currents are induced by 
the rapidly interrupted or alternating currents 
in the primary coil. (See Coil, Induction. 
Transfor?ner.) 

Coil, Shunt A coil placed in a de- 
rived or shunt circuit, (See Circuit, Shunt?) 

Coil, Spark A coil of insulated wire 

connected with the main circuit in a system 
of electric gas-lighting, the extra spark pro- 




Fig. 14Q. Spark Coil. 

duced on breaking the circuit of which is em- 
ployed for electrically igniting gas jets. 

Spark coils are employed where the number of 



gas jets to be simultaneously lighted is not too 
great. When this number exceeds certain limits, 
the spark from an induction coil is more advan- 
tageously used. 
A spark coil is shown in Fig. 149. 

Coils, Armature, of Dynamo-Electric 

Machine The coils, strips or bars that 

are wound or placed on the armature core. 

To avoid needless resistance the wire, or other 
conductor, of the armature coils, should be as 
short and thick as will enable the desired electro- 
motive force to be obtained without excessive 
speed of rotation. 

The armature coils should enclose as many 
lines of force as possible (i. e., they should have 
as nearly a circular outline as possible). In 
drum-armatures, the breadth of the armature is 
frequently made nearly equal to its length, unless 
other considerations prevent. 

When the armature wire consists of rods or 
bars, it should be laminated or slit in planes 
parallel to the lines of force so as to avoid 
eddy currents. Other things being equal, the 




Fig. ijo. Series Connection of Armature Coils. 

greater the number of coils, the more uniform 
the current generated. The separate coils should 
be symmetrically disposed; otherwise irregular in- 
duction, and consequent sparking at the commu- 
tator results. 

The coils of pole-armatures should be wound near 
the poles rather than on the middle of the cores. 
In order to avoid undue heating, spaces for 
air ventilation are not inadvisable. Various con- 
nections of the armature coils are used. 

In some machines all the coils are connected in 
a closed circuit. In some, the coils are independ- 
ent of one another, and, either for the entire 
revolution, or for part of a revolution, are on an- 
open -circuit. 



Coi.] 



111 



[Col. 



In alternating current dynamos in order to ob- 
tain the rapid reversals or alternations of current, 
which in some machines are as high as 12,000 
per minute, a number of poles of alternate polar- 
ity are employed. The separate coils that are 
used on the armature may be coupled either in 
series or in multiple-arc. 

Where a comparatively low electromotive force 
is sufficient, such as for incandescent lamps in 
multiple-arc, the separate coils are united in 
parallel; but for purposes where a considerable 
electromotive force is necessary, as for example, 
in systems of alternate current distribution, with 
converters at considerable distances from the 
generating dynamo, they are often connected in 
series, as shown in Fig. 150. 

Coils, Binding Coils of wire wound 

on the outside of the armature coils, and at 
right angles thereto, to prevent the loosening 
of the armature wires by the action of cen- 
trifugal force. 

The binding coils are generally made of hard 
brass wire. 

Coils, Compensating- A term some- 
times applied to the series coils placed on a 
shunt-wound dynamo. 

Coils, Conjugate — Two coils so 

placed, as regards each other, that an interrup- 
tion of the current in one produces no induced 
current in the other. 

When two coils are conjugate to each other, the 
lines of force of one do not pass through the other. 
Consequently such coils can produce no induc- 
tion in one another. 

Coils, Henry's A number of sepa- 
rate induction coils so connected that the 
currents induced in the secondary wire of 
the first coil, are caused to induce currents 
in the secondary wire of the second coil, with 
whose primary it is connected in series, and 
so on throughout all the coils. 

A series of three of Henry's coils is shown in 
Fig. 151. An intermittent battery current is sent 

d f 




secondary, d, of the second coil, is connected with 
the primary, e, of the third coil, and the cur- 
rents finally induced in f, are employed for any 
useful purpose, such as the magnetization of a 
bar of iron at g. 

The current in b, is sometimes called a Secon- 
dary Current, or a Current of the Second" Order; 
that induced by this secondary current in d, is 
called a Tertiary Current, or a Current of the 
Third Order ; that in f, a Current of the Fourth 
Order. Henry carried these successive induc- 
tions up to currents of the Seventh Order. 

Henry's coils in reality consist of separate in- 
duction coils, connected, as above explained, in 
series. 

In Fig. 152, the tertiary current induced in 

e 
IV 




Fig. 132. Tertiary Currents of Coils. 
IV, may be employed to give shocks to a person 
grasping the handles, e and f. 

Coils, Proportional Pairs of re- 
sistance coils, generally of 10, 100 and 1,000 
ohms each, forming the proportional arms of 
the balance or bridge, and employed in the box, 
or commercial form of Wheatstone's bridge. 
(See Bridge, Electric, Commercial Form 
of) 

Cold, Production of, Iby Electricity 

— An absorption of energy and consequent 
reduction of temperature at a thermo-electric 
junction by the passage of an electric current 
across such junction in a certain direction. 

When an electric current passes across a thermo- 
electric junction, the junction is either heated or 
cooled. In the case of an antimony-bismuth 
couple, if the current passes from the antimony 




Fig. IJI. Henrys Coils. 
into a, the secondary, b, of which is connected 
with the primary, c, of the second coil. The 



A B 

Fig. 1 J 3. Freezing of Water by Electricity. 

to the bismuth the junction is heated; if it passes 
from the bismuth to the antimony it is cooled 
In the apparatus shown in Fig. 153, the antimony- 
bismuth couple is arranged as shown for the 



Col.] 



112 



[Com. 



freezing of water by means of the electric cur- 
rent. A and B, represent plates of antimony and 
bismuth respectively. A small cavity, at E, serves 
to hold a drop of water. When a current has 
passed in the direction shown by the arrows, a 
drop of water, previously cooled to the tempera- 
ture of melting ice, is solidified by the lowering 
of the temperature at the junction. 

Collecting" Brushes of Dynamo-Electric 
Machine. — (See Brushes, Collecting, of 
Dynaino-Electric Machine?) 

Collectors, Electric Devices em- 
ployed for collecting or taking off electricity 
from a moving electric source. 

Collectors of Electric Frictional Ma- 
chines. — The metallic points that collect the 
charge from the glass plate or cylinder of a 
frictional electric machine. 

Collectors of Dynamo Electric Machines. 
— The brushes that rest on the commutator 
cylinder, and carry off the current generated 
on the rotation of the armature. 

Collectors are properly called commutators 
when they are employed to cause an alternate 
current to become continuous, or to flow in one 
and the same direction. 

Colloids. — One of the two classes into 
which substances are separated by dialysis. 

By dialysis bodies are separated into crystal- 
loids, or bodies capable of crystallizing, and col- 
loids or jelly-like bodies, incapable of crystallizing. 
Colloids possess great cohesion and but slight 
diffusibility. (See Dialysis.") 

ColomMn. — An insulating substance, con- 
sisting of a mixture of sulphate of barium 
and sulphate of calcium, placed between the 
parallel carbons of the Jablochkoff candle. 

Column, Barometric — A column, 

usually of mercury, approximately 30 inches 
in vertical height, sustained in a barometer, 
or other tube, by the pressure of the atmos- 
phere. 

The space above the barometric column con- 
tains a vacuum known as the Torricellian vac 
uum. (See Vacuum, Torricellian.} 

Column, Electric A term formerly 

applied to a voltaic pile. (See Pile, Voltaic?) 
Colza Oil.— (See Oil, Colza.) 



Combination Gas Fixtures. — (See Fix- 
tures, Gas, Combination.) 

Combined Tangent and Sine Galvanom- 
eter. — (See Galvanometer, Combined Tan- 
gent and Sine?) 

Comb Lightning- Arrester. — (See Arrester y 
Lightning, Comb?) 

Comb Protector. — (See Protector, Comb?) 

Commercial Efficiency. — (See Efficiency, 
Com?nercial?) 

Commercial Efficiency of Dynamo.— 
(See Efficiency, Coinmercial, of Dynamo?) 

Commercial Form of Electric Bridge.— 
(See Bridge, Electric, Commercial Form of?) 

Communicator, Electric A term 

formerly employed for a telegraphic key. (See 
Key, Telegraphic?) 

Commutating Transformers, Distribu- 
tion of Electricity by (See Elec- 
tricity, Distribution of, by Conimutating 
Transformers?) 

Commutation. — The act of commuting, as 
of currents. 

Commutation, Diameter of In a 

dynamo-electric machine a diameter on the 
commutator cylinder on one side of which 
the differences of potential, produced by the 
movement of the coils through the magnetic 
field, tend to produce a current in a direction 
opposite to those on the other side. 

That diameter on the commutator cylinder 
of an open-circuited armature that joins the 
points of contact of the collecting brushes. 

Thus in Fig. 154, the directions of the induced 
electromotive forces are indicated by the arrows. 
The diameter of commutation is therefore the line 
n n'. The term neutral line is also sometimes 
given to this line. It lies at right angles to the 
line of maximum magnetization m m. 

In a closed-circuited armature, that is, in an arm- 
ature the coils of which are connected in a closed 
circuit, the collecting brushes rest on the commu- 
tator cylinder at the neutral line, or on the diame- 
ter of commutation. 

In an open -circuited armature, however, where 
the coils are independent of each other, the 
collecting brushes must be set at m m, at right 
angles to the neutral line n n. The term diame- 



Com.] 



113 



[Com. 



ter of commutation is, therefore, often applied to 
this second position. According to this use of the 




Fig. IS 4- Diameter of Commutation. 

term, the diameter of commutation is that diameter 
on the commutator which joins the points of con- 
tact of the collecting brushes. 

The neutral linenn', Fig. 154, it will be noticed 
does not occupy a vertical position, but is dis- 
placed somewhat in the direction of rotation, thus 
necessitating the shifting of the brushes forward 
in the direction of rotation. This necessary shift- 
ing of the brushes is known technically as the 
lead of the brushes. (See Lead, Angle of.) 

It will thus be seen that the term diameter of 
commutation is used in two different senses. 

In reality, the term refers to the position of cer- 
tain points on the commutator as distinguished 
from points on the armature coils. On the com- 
mutator, the diameter of commutation is the line 
drawn through the two commutator bars at which 
the currents from the two sides are opposed to 
each other. 

It is evident that the commutator may be inten- 
tionally twisted with respect to the armature, so 
as to bring its diameter of commutation into any 
desired convenient position. 

Commutation, Dissymmetry of 

A commutation in which the neutral line does 
not coincide with a diameter of the commu- 
tator. (See Commutation, Diameter of.) 

Commutator.— In general, a device for 
changing the direction of an electric current. 

Commutator, Burning 1 at — Arcing 

and consequent destructive action on the 
commutator segments of a dynamo-electric 
machine. 

When the arcing is pronounced, the intense 
heat soon destroys the commutator. 

Commutator Cylinder, Neutral-Line of 

(See Line, Neutral, of Commutator 

Cylinder?) 



Commutator, Dynamo-Electric Machine 

That part of a dynamo-electric ma- 
chine which is designed to cause the alter- 
nating currents produced in the armature to 
flow in one and the same direction in the ex- 
ternal circuit. 

One end of an armature coil is connected witii 
A', Fig. 155, and the 
other with A. The brushes 
are so set that A, and A', 
are in contact with B', 
and B, respectively, as 
long as the current flows 
in the same direction in the 
armature coil connected 
therewith, but enter into 
contact with B, and B', Fig. zjS- Commutator 
when the current changes of Dynamo - Electric 

its direction, and continue Machine. 
in such contact as long as it flows in this direc- 
tion. By the use of a commutator the current 
will therefore flow through any circuit connected 
zvith the brushes in one and the same constant 
direction. 





Two-part Commutator. 



In action, the commutator is subject to wear 
from the friction of the brushes, and the burning 
action of destructive sparks. The commutator 




Fig. IS 7- Two-part 
Commutator. 



Fig. 158. Two-part 
Commutator. 



segments are, therefore, made of comparatively 
thick pieces of metal, insulated from one another, 



Com.] 



114 



[Com. 




and supported on a commutator cylinder usually- 
placed on the shaft of the armature. 

The ends of the armature coils are connected 
to commutator strips or segments. 

The number of metallic pieces or segments, A. 
and A', on the commutator cylinder depends on 
the number, arrangement and connection of the 
armature coils, and on the 
disposition of the magnetic 
field of the machine. 

Figs. 156, 157 and 158 
show the connections of an 
armature coil to the plates of 
a two-part commutator. 

A four-part commutator 

for a ring. armature, and the lg ' '^ Q ' ^ ur 'P ar 

Commutator. 

connections of the coils 

thereto, are shown in Fig. 159. 

The commutator strips may either connect the 
separate coils in a closed-circuited armature, in 
which the coils are all connected with one an- 
other, or, in an open -circuited armature, in which 
the separate coils are independent of one another. 

Commutator, RuhmkoriFs A name 

given by Ruhmkorff to a device placed on his 
induction coil for the purpose of changing or 
reversing the direction of the battery current 
through the primary. t 

This reverser is shown in Fig. 160. (See 
Coil, Ruhmkorff.) 

V 




Fig. ibo. Ruhmkorff J Commutator. 

Two metallic strips, V, V, supported on a 
cylinder of insulating material, are in contact with 
the battery terminals A, and D, through two 
vertical springs that bear on them. On a half 
rotation of the cylinder by the thumb screw L, 



the strips V, V, change places as regards the ver- 
tical springs, and thus reverse the direction of 
the battery current. 

Commuted Currents. — (See Currents, 
Commuted?) 

Commuter, Current — Any appa- 
ratus by means of which electrical currents, 
flowing alternately in different directions, 
may be caused to flow in one and the same 
direction. 

A Commutator. 

Commuting. — Causing to flow in one and 
the same direction. 

Commuting Currents. — (See Currents, 
C o?)i7 fiutzng.) 

Compartment Manhole of Conduit. — (See 
Ma,7ihole, Co77ipart77ie7it, of Co7iduit.) 

Compass, Azimuth — A compass 

used by mariners for measuring - the horizon- 
tal distance of the sun or stars from the mag- 
netic meridian. (See Azimuth, Mag7ietic.) 

A mariner's Compass. 

A single magnetic needle, or several magnetic 
needles, are placed parallel to one another on the 
lower surface of a card, called the compass card. 
This card is divided into the four cardinal points, 
N, S, E and W, and these again subdivided into 
thirty-two points called Rhumbs. 

In the azimuth compass these divisions are sup- 
plemented by a further division into degrees. 

A form of azimuth compass is shown in Fig. 
161. In order to maintain the compass box in a 




Fig. ibi. Azimuth Compass. 

horizontal position, despite the rolling of the ship, 
the box, A\B, is suspended in the larger box, P 
Q, on two concentric metallic circles, C D, and 



Com.] 



lib 



[Com. 



E F, pivoted on two horizontal axes at right angles 
to each other. This kind of support is technic- 
ally termed Gimbals. Sights G, H, are provided 
for measuring the magnetic azimuth of any ob- 
ject. 

Compass, Boxing the —Naming, 

consecutively, all the different points or 
rhumbs of the compass from any one of them. 
(See Compass, Points of.) 

Compass-Card. — (See Card, Compass) 

Compass, Inclination A magnetic 

needle moving freely in a single vertical plane, 
and employed for determining the angle of 
vdip at any place. 

An Inclinometer. (See Inclinometer) 
A dipping circle. (See Circle, Dipping) 
The needle M, Fig. 162, is supported on knife 




Fig. 162 Inclination Compass. 

edges so as to be free to move only in the vertical 
plane of the graduated vertical circle C C. This 
circle is movable over the horizontal graduated 
circle H II. In order to determine the true angle 
of dip, the vertical plane in which the needle is 
free to move must be placed exactly in the plane 
•of the magnetic meridian. 

To ascertain this plane the vertical circle is 
•moved until the needle points vertically down- 
wards. It is then in a plane 90 degrees from the 
magnetic meridian. The vertical circle is then 
moved over the horizontal circle 90 degrees, in 
which position it is in the plane of the magnetic 
meridian, when the true angle of the dip is read off. 

For an explanation of the reason of this see 



Component, Horizontal and Vertical, of the 

Earth'' s Magnetism. 

Compass, Mariner's A name often 

applied to an azimuth compass. (See Com- 
pass, Azi?nuth) 

Compass, Points of The thirty-two 

points into which a compass card is divided. 

Sixteen of these points are shown in Fig. 163. 




Fig. 163. Points of Compass. 

The position of the remaining points will be 
readily seen by an inspection of the figures. 
These points are as follows: 



1. North. 

2. N. by E. 

3. N. N. E. 

4. N. E. by N. 

5. N. E. 

6. TST. E. by E. 

7. E. N. E. 

8. E. by N. 

9. East. 
io. E. by S. 

11. E. S. E. 

12. S. E. by E. 

13. S. E. 

14. S. E. by S 

15. S. S. E. 

16. S. by E. 



17. South. 

18. S. by W. 

19. S. S. w. 

20. S. W. by S. 

21. S. W. 

22. S. W. by W. 

23. W. S. W. 

24. W. by S. 

25. West. 

26. W. by N. 

27. W. N. W. 

28. N. W. by W. 

29. N. W. 

30. N. W. by N. 

31. N. N. W. 

32. N. by W. 



Boxing the Compass consists in naming all 
these points consecutively from any one of them. 

The flirection in which the ship is sailing is de- 
termined by means of a point fixed on the inside of 
the compass box, directly in the line of the ves- 
sel's bow. 

Compass, Ehumbs of The points 

of a mariner's compass. (See Compass, 
Points of) 



Com.] 116 

Compensated Alternator*— (See Alter- 
nator, Compensated!) 

Compensated Excitation of Alternator. 

— (See Alternator, Compensated Excita- 
tion of.) 

Compensating Coils. — (See Coils, Com- 
pensating) 

Compensating Magnet. — (See Magnet, 
Compensating.) 

Complement of Angle.— (See Angle, Com- 
plement of.) 

Completed-Circuit. — (See Circuit, Com- 
pleted.) 

Component. — One of the two or more sep- 
arate forces into which any single force may 
be resolved ; or, conversely, the separate forces 
which together produce any single resulting 
force. 

When two or more forces act simultaneously to 
produce motion in a body, the body will move 



[Com. 




Fig. lb 4. Composition of Forces. 



with a given force in a single direction called the 
resultant. The separate forces, or directions of 
motion, are called the components. 

Two forces acting simultaneously on a body at 
A, Fig. 164, tending to move it in the direction 




Fig 165. Resolution of Ftrces. 

of the arrows, along A B, and A C, with intensi- 
ties proportioned to the lengths of the lines A B, 
and A C, respectively, will move it in the direc- 
tion A D, obtained by drawing B D, and D C, 



parallel to A C, and A B, respectively, and then 
drawing A D, through the point of intersection, 
D. This is called the Composition of Forces. 
A D, is the resultant force, and A B and A C, 
are its components. 

Conversely, a single force, acting in the direc- 
tion of D B, Fig. 165, against a surface, B C, 
may be regarded as the resultant of the two sep- 
arate forces, D E, and D C, one parallel to C B, 
and one perpendicular to it. D E, being parallel 
to C B, produces no pressure, and the absolute 
effect of the force will, therefore, be represented 
by C D. 

This separation of a single force into two or 
more separate forces is called the resolution of 
forces, the force, D B, being resolved into the 
components, D E and D C. 

Component Currents. — {See Currents, 
Component!) 

Component, Horizontal, of Earth's Mag- 
netism That portion of the earth's 

directive force which acts in a horizontal di- 
rection. 

That portion of the earth's magnetic force 
which acts to produce motion in a com- 
pass needle free to move in a horizontal plane 
only. 

Let A B, Fig. 166, represent the direction and. 
magnitude of the earth's magnetic field on a mag- 
netic needle. The magnetic force will lie in the 
plane of the magnetic merid- 
ian, which will be assumed to 
be the plane of the paper C A 
D. The earth's field, A B, can 
be resolved into two compo- 
nents, A D, the horizontal com- 
ponent, and A C, the vertical 
component. 

In the case of a magnetic j 
needle, like the ordinary com- 
pass needle, which is free to 
move in a horizontal plane only, 
the horizontal component alone 
directs the needle. A weight 
is applied to balance the vertical 
component. 

When the needle is free to move in a vertical 
plane, and this plane corresponds with that of 
the magnetic meridian, the entire magnetic force, 
A B, acts to place the needle, supposed to be 
properly balanced, in the direction of the lines of 
force of the earth's magnetic field at that point. 




B 

Fig. ibb. Com- 
ponents of Earth's 
Magnetism. 



Com.] 

Component, Vertical, of Earth's Magnet- 
ism —That portion of the earth's 

directive force which acts in a vertical direc- 
tion. 

In the vertical plane at right angles to the plane 
of the magnetic meridian, the vertical component 
alone acts, and the needle points vertically down- 
wards, in no matter what part of the earth it 
may be. In Fig. 166, A C, is the vertical com- 
ponent of the earth's directive force. 

Composite Balance. — (See Balance, Com- 
posited) 

Composite-Field Dynamo. — (See Dynamo, 
Composite-Field.) 

Composition ot Forces. — (See Forces, 
Composition of.) 

Compound Arc. — (See Arc, Compound) 

Compound, Binary In chemistry, 

a compound formed by the union of two 
different elements. 

Water is a binary compound, being formed by 
the union of two atoms of hydrogen with one 
atom of oxygen. Its composition is expressed in 
chemical symbols, H 2 0, which indicates that two 
atoms of hydrogen are combined, or chemically 
united, with one atom of oxygen. Water is 
therefore a binary compound, because it is formed 
of two different elementary substances. 

Compound, Chatterton's A com- 
pound for cementing together the alternate 
coatings of gutta-percha employed on a cable 
conductor, or for filling up the space between 
the strand conductors. 

The composition of Chatterton's compound is 
as follows: 

Stockholm tar I part by weight. 

Resin I " " 

Gutta-percha 3 " " 

— {Clark &= Sabine.) 

Compound Circuit. — (See Circuit, Com- 
pound^ 

Compound, Clark's A compound 

for the outer casing of the sheathing of sub- 
marine cables. 

The composition of Clark's compound is as fol- 
lows: 



117 [Con. 

Mineral pitch ..... 65 parts by weight. 

Silica 30 " " 

Tar 5 « 

— {Clark &> Sabine.) 

Compound - Horseshoe Magnet. — (See 
Magnet, Compound-Horseshoe?) 

Compound Magnet. — (See Magnet, Com- 
pound) 

Compound Radical. — (See Radical, Com- 
pound) 

Compound-Winding of Dynamo-Electric 
Machines. — (See Winding, Compound, of 
Dynamo-Electric Machine) 

Compound- Wound Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric, 
Compound- Wound) 

Compound- Wound Motor.— (See Motor, 
Compound- Wound.) 

Concentration of Lines of Force.— (See 
Force, Lines of, Concentratio?i of) 

Concentric Carbon Electrodes. — (See 
Electrodes, CoJicentric Carbon) 

Concentric Cylindrical Carbons. — (See 
Carbons, Concentric Cylindrical) 

Condenser.— A device for increasing the 
capacity of an insulated conductor by bring- 
ing it near another insulated earth-connected 
conductor, but separated therefrom by any 
medium that will readily permit induction to 
take place through its mass. 

A variety of electrostatic accumulator. 

If the conductor A, Fig. 167, standing alone 




Fig. 1 6 J. JEpinns Air Condenser. 

and separated from other conductors, be con- 
nected with an electric machine, it will receive 
only a very small charge. 



€on.] 



118 



[Con. 



If, however, it be placed near C, but separated 
from it by a dielectric, such as a plate of glass 
B, and C, be connected with the ground, A, will 
receive a much greater charge. (See Dielectric.') 

Suppose, for example, that A, be connected 
with the positive conductor of a factional electric 
machine, it will by induction establish a negative 
charge on the surface C, nearest it, and repel 
a positive charge to the earth. The presence of 
these two opposite charges on the opposed sur- 
faces of A and C, permits A, to receive a fresh 
charge from the machine. (See Induction, 
Electrostatic.) 

The charge in a condenser in reality resides 
on the opposite surfaces of the glass, or other 
dielectric separating the metallic coatings, as can 
be shown by removing the coatings after charg- 
ing. 

The condenser resulted from the discovery of 
the Leyden jar. (See Jar, Leyden.) 

The capacity of a condenser is measured in 
microfarads. (See Farad.) 

In practice condensers are made of sheets of 
tin foil, connected to A and B, respectively, and 
separated from one another by sheets of oiled 
silk, paraffined paper, or thin plates of mica, as 
shown in Fig. 168. 




Fig. 1 68. Condenser. 

A Leyden jar or condenser does not store elec- 
tricity any more than a storage battery does. 
The same quantity of electricity passes out of the 
opposite coating of the jar that is passed into the 
other coating. The jar, therefore, possesses no 
store of electricity. What it really possesses is a 
store of electrical energy. 

According to Ayrton, if the capacity of a con- 
denser, in farads, be F, and the difference of po- 
tential, with which it is charged, be V, volts, the 
store of electric energy it possesses, or the work it 
can do when discharged, is, 

F X V2 

Work = foot-pounds. 

2.712 ^ 

Condenser, Adjustable — A con- 
denser, the plates of which can be readily 
adjusted so as to obtain the same capacity 
as that of the conductor to be measured. 



In order to obtain a comparatively wide range 
of adjustability, a condenser is composed of say 
four separate sections: consisting of one of 2 
microfarads, one of I microfarad and two of $ 
microfarad, thus making in all 4 microfarads. 

Condenser, iEpinus A name given 

to an early form of condenser. (See Con- 
denser^ 

Condenser, Air — A condenser in 

which layers of air act as the dielectric. 

A form of air condenser is shown in Fig. 169. 




Fig. ibq. Air Condenser. 

It consists essentially of one set of thin plates of 
glass partially coated on both sides with sheets of 
tin foil, so as to leave uncoated a space of about 
one inch around the edge of the glass. The glass 
plates do not act as dielectrics, but merely as sup- 
ports for the tin foil, hence the foil on both sides 
of the plates is connected electrically. 

Another set of plates alternating with the above 
have the tin foil placed over the whole surface of 
the glass. 

These plates are placed, alternately, over one 
another on a stand between guide rods of vulcan- 
ite E, E, E, E, in the manner shown, and are 
separated from one another by fragments of glass 
of the same thickness. The plates with the foil 
over their entire surface are all connected to- 
gether and to the terminal B, to form the outer 
coating, and the plates with the foil over nearly 
all their surfaces are all connected together and 
to the terminal A, to form the inner coating of 
the condenser. 

There is thus formed a condenser in which 
practically two extended conducting surfaces are 



Con.] 



119 



[Con. 



separated from each other by a thin layer of air, 
which acts as the dielectric. 

Condenser, Alternating-Current 

A condenser suitable for use in connection with 
a system for the distribution of electric energy 
by means of alternating currents. 

Alternating-current condensers must have a very 
thin dielectric in order to avoid too great bulk. 
This, of course, introduces a difficulty as regards 
liability of failure of insulation, which must be 
carefully avoided. 

Condenser, Armature of (See Arm- 
ature of a Condenser.) 

Condenser, Capacity of The quan- 
tity of electricity in coulombs a condenser is 
capable of holding before its potential in volts 
is raised a given amount. 

The ratio between the quantity of electric- 
ity in coulombs on one coating and the poten- 
tial difference in volts between the two coat- 
ings. — [Ayr ton.) 

The capacity is directly proportional to the 
charge Q. and inversely proportional to the po- 
tential V, or, 



K = 



or, since Q = K V, the quantity of electricity re- 
quired to charge a condenser to a given potential 
is equal to the capacity of the condenser multi- 
plied by the potential through which it is carried. 

The capacity of a condenser increases in direct 
proportion to the increase in the area of its coat- 
ings. 

When the coatings are plane and parallel to 
«ach other, the capacity of the condenser is in the 
inverse ratio to the distance between the coatings. 

Condenser, Coating of (See Coat- 
ing of Condenser.) 

Condeuser, Plate -A condenser, the 

metallic coatings of which are placed on 
suitably supported plates. 

Condenser, Poles of — - —(See Poles of 
Condenser.) 

Condenser, Time-Constant of 

The time in which the charge of a condenser 

falls to the 1-2.7 1828 part of its original 
value. 

Condensers, Distribution of Electricity 
by Means of ? (See Electricity, Distri- 



bution of. by Alternating Currefits, by means 
of Condensers . Electricity, Distribution of, 
by Continuous Citrrents, by mea?is of Con- 
densers.) 

Conduct. — To pass electricity through con- 
ducting substances. 

To determine the general direction in which 
electricity shall pass through the ether or 
dielectric surrounding the so-called conduct- 
ing substance. (See Conductio?i, Electric.) 

Conductance. — A word sometimes used in 
place of conducting power. 
Conductivity. 

Conductance, Magnetic — A word 

sometimes used instead of magnetic permea- 
bility. (See Permeability Magnetic :) 

The magnetic conductance is equal to the total 
induction through the circuit divided by the 
magnetizing force. 

Conducting Cord.— (See Cord, Conduct- 
ing.) 

Conducting, Electrical Possessing 

the power of passing electricity through any 
conducting substance. 

Possessing the power of determining the 
direction in which electricity shall pass through 
the ether surrounding a substance. (See 
Conductor.) 

Conducting Power. — (See Power Con- 
ducting^) 

Conducting Power for Electricity. — (See 
Power, Conducting, for Electricity.) 

Conducting Power for Lines of Mag- 
netic Force. — (See Force, Magnetic, Lines 
of, Conducting Power of,) 

Conducting Power, Tables of 

(See Power, Conducting, Tables of.) 

Conduction Current. — (See Current, Con- 
duction.) 

Conduction, Disruptive A species 

of conduction in which the resistance of the 
conductor is suddenly overcome. 

Disruptive conduction is seen in the disruptive 
discharge of a condenser, or Leyden jar. 

Conduction, Electric The so- 



Con.] 



120 



[Con. 



called flow or passage of electricity through 
a metallic or other similarly acting substance. 

The ability of a substance to determine the 
direction in which electric energy shall be 
transmitted through the ether surrounding it. 

The ability of a substance to determine the 
direction in which a current of electricity 
passes from one point to another. 

When a conducting wire has its ends connected 
with an electric source, a current of electricity is, 
in common language, said to flow through the wire, 
and this was formerly believed to be a correct 
statement. According to modern views, however, 
the electric energy is believed to pass through the 
ether or other dielectric surrounding the con- 
ductor, the so-called conductor forming merely 
a sink, where the electrical energy dissipates 
itself. Tne conductor simply acts to direct the 
current. 

Since, however the energy practically passes 
by means of, and in the general direction of the 
conductor, there is no objection in speaking of 
the electricity as flowing through the conductor. 

Conduction, Electric, Disruptive 

A conduction of electric energy which ac- 
companies a disruptive discharge. (See 
Discharge, Disruptive^) 

Conduction, Electric, Metallic A 

conducting of electric energy of the same char- 
acter as that which occurs in metallic sub- 
stances. 

Conduction, Electrolytic A term 

sometimes employed to indicate the passage 
of electricity through an electrolyte. 

There is no passage of electricity through an 
electrolyte in the same sense as through an ordi- 
nary conductor. 

When, through electrolysis, an electromotive 
force is brought to bear on a molecule of say 
HC1, it is assumed by some that the liberated 
hydrogen atoms travel on the whole in one di- 
rection, and the liberated chlorine atoms in the 
opposite direction. The atoms thus moving 
through the liquid may by their electric charges 
be assumed to convey electricity, and this fact 
has given rise to the term electrolytic conduc- 
tion. 

In electrolytic conduction the charges are 
necessarily equal, but the speeds of their motion 
are unequal. In a given liquid, each atom has 



its own rate of motion, no matter with what it 
has been combined. Hydrogen travels faster 
than any other kind of atom. The conductivity 
of a liquid depends on the sum of the speeds with 
which the two opposed atoms travel. 

This assumed double stream of oppositely mov 
ing atoms is denied by most physicists. (See 
Hypothesis, Grotthus . ) 



Conductive-Discharg-e.- 

Conductive.) 



(See Discharge, 
The recip- 



Conductivity, Electric — 

rocal of electric resistance. 

Since the conductivity is greater the less the re- 
sistance, the conductivity will be equal to the recip- 
rocal of the resistance, and may be so defined. The 

conductivity is therefore equal to 

Conductivity, Equivalent A con- 
ductivity equal to the sum of several conduc- 
tivities. 

Conductivity per Unit of Mass.— The re- 
ciprocal of the resistance of a substance per 
unit of mass. 

Conductivity per Unit of Volume. — The 
reciprocal of the resistance of a substance 
per cubic centimetre or per cubic inch. 

The resistance is measured from one face of 
the cube to the opposite fa^e. 

Conductivity Resistance. — (See Resist- 
ance, Conductivity.) 

Conductivity, Specific The par- 
ticular conductivity of a substance for elec- 
tricity. 

The specific or particular resistance of a 
given length and unit of cross-section of a 
substance as compared with the same length 
and area of cross-section of some standard 
substance. 

Conductivity, Specific Magnetic 

The specific or particular permeability of a 
substance to lines of magnetic force. 

The specific magnetic conductivity is measured 
by the ratio of the magnetization produced to the 
magnetizing force which produces it. 

The specific magnetic conductivity is the an- 
alogue of specific inductive capacity, or conduc- 
tivity for lines of electrostatic force. It is also the 
analogue for specific conducting power for heat. 



€on.] 



12 i 



[Con. 



Conductor. — A substance which will per- 
mit the so-called passage of an electric current. 

A substance which possesses the ability of 
determining the direction in which electricity 
shall pass through the ether or other dielec- 
tric surrounding it. 

Some electrolytes, such, for example, as vari- 
ous mixtures of sulphuric acid and water, possess 
a true power of conducting electricity, and there- 
fore have a specific resistance. Generally, how- 
ever, the passage of the electrolyzing current is 
regarded as different from that of a current which 
merely heats the conductor. 

The space or region around a conductor 
through which an electric current is passing has 
a magnetic field produced in it. 

The term conductor is opposed to non-conductor, 
or a substance which will not permit the passage 
of an electric current through it after tne manner 
of a conductor. 

The terms conductors and non-conductors are 
only relative. There are no such things as 
either perfect conductors or perfect non con- 
ductors. 

Conductors in general, are distinguished from 
electrolytes, in that the latter do not allow the 
electricity to pass save by undergoing a chemical 
decomposition. 

Conductor, Anisotropic A con- 
ductor which, though homogeneous in struc- 
ture like crystalline bodies, has different 
physical properties in different directions, just 
as crystals have different properties in the 
direction of their different crystalline axes. 

Anisotropic conductors possess different powers 
of electric conduction in different d.rections. 
But in opposite directions along thi same axis their 
conductivity is equal. They differ in this respect 
from isotropic conductors. (See Conductor, Iso- 
tropic. ) 

Conductor, Anti-Induction —A con- 
ductor so constructed as to avoid injurious 
inductive effects from neighboring telegraphic 
or electric light and power circuits. 

Such anti-induction conductors sometimes con- 
sist of a conductor for constant currents and a 
metallic shield surrounding the conductor, and 
designed to prevent induction from taking place 
in the wire itself. 

The anti-induction conductor generally con- 



sists of twin conductors surrounded by ordinary 
insulation and sometimes enclosed by some form 
of metallic shield, in order to prevent the action 
of electrostatic induction. 

When a periodic current is to be transmitted 
through a conductor, the most effective way of 
annulling its inductive effects on neighboring cir- 
cuits is to place the lead of the conductor in the 
axis of another conductor, used as a return. In 
other words, to employ concentric cylinders, in- 
sulated from one another and from the earth. 
Under these conditions, calling the current in one 
direction positive, and in the other direction 
negative, the shielding action will be perfect 
when the algebraic sum of the currents in the 
core and sheath are zero. 

The same effect is obtained in metallic circuits, 
by placing the leads parallel to the return, and 
crossing and recrossing the wires repeatedly. 
(See Connection, Telephonic Cross.) 

Elihu Thomson renders ordinary telephone 
conductors, arranged as single lines with earth 
returns, free from induction by means of the 
counter-electromotive force produced in a coil of 
wire by the disturbing cause. 

In applying this system to the case of an elec- 
tric arc or power line passing alongside a tele- 
phone line, a wire coil, whose turns are pro- 
portioned in number to the induction to be bal- 
anced, is introduced into the electric light line 
and placed near another coil of finer wire inserted 
as a loop in the telephone circuit. The second coil 
is placed parallel to or inclined at an angle to the 
first coil. In practice, the second coil is inclined 
until the counter-induction set up in the tele- 
phone wire is equal to that produced in the main 
line, and silence is thus produced, so far as in- 
duction is concerned, in the telephone. 

Conductor, Armored A conduc- 
tor provided with a covering or sheathing of 
metal placed over the insulating covering for 
protection from abrasion or external wear. 

Armored conductors are used in situations 
where the conductor is exposed to abrasion or 
other external wear. 

Conductor, Branch — A conductor 

placed in a shunt circuit. (See Circuit, 
Shunt.) 

Conductor, Closed-Circuited — A 

conductor connected as a closed or com- 
pleted circuit. 



Con.] 



122 



[Con. 



Conductor, Conjugate In a system 

of linear conductors, any pair of conductors 
that are so placed as regards each other that 
a variation of the resistance or the electro- 
motive force in the one causes no variation in 
the current of the other. 

Conductor, Earth- Circuited —A 

conductor connected to the ground, or to an 
earth-connected circuit. 

Conductor, House-Service A term 

employed in a system of multiple incan- 
descent lamp distribution for that portion of 
the circuit which is included between the ser- 
vice cut-out and the centre or centres of dis- 
tribution, or between this cut-out and one or 
more points on house mains. 

Conductor, Isotropic A conduc- 
tor which possesses the same powers of elec- 
tric conduction in all directions. 

An electrically homogeneous conducting 
medium. 

Conductor, Leakage A conductor 

placed on a telegraph circuit for the purpose 
of preventing the disturbing effects of leakage 
into a neighboring line by providing a direct 
path for such leakage to the earth. 

The leakage conductor, as devised by Varley 
consists of a thick wire attached to the telegraph 
pole. The lower end of the conductor is grounded, 
and its upper end projects above the top of the 
pole. 

There exists some doubt in the minds of expe- 
rienced telegraph engineers whether it is well to 
apply leakage conductors to telegraphic or tele- 
phonic lines of over 12 or 15 miles in length, 
since such conductors greatly increase the electro- 
static capacity of the line, and thus cause serious 
retardation. 

Conductor, Lightning- — A term 

sometimes used for a lightning rod. (See 
Rod, Lightning.) 

Conductor, Open-Circuited — A con- 
ductor arranged as an open or broken circuit. 

Conductor, Potential of —The rela- 
tion existing between the quantity of elec- 
tricity in a conductor and its capacity. 

A given quantity of electricity will raise the 



potential of a conductor higher in proportion as 
the capacity of the conductor becomes less. 

Conductor, Potential of, Methods of 
"Varying The potential of a conductor 

may be varied in the following ways ' 

(I.) By varying its electric charge. 

(2.) By varying its size or shape without alter- 
ing its charge. 

(3.) By varying its position as regards neigh- 
boring bodies. 

This resembles the case of a gas whose tension 
or pressure may be varied as follows, viz.: 

(1.) By varying the quantity of gas. 

(2.) By varying the size of the gas holder in 
which it is kept, and 

(3.) By varying the temperature. 

Difference of potential, therefore, corresponds — 

(1.) With difference of level in liquids. 

(2. ) With difference of pressure in gases. 

(3.) With difference of temperature in heat. 

— {Ayr ton.) 

Conductor, Prime —The positive 

conductor of a frictional electric or electro- 
static machine. (See Machine, Frictional 
Electric.) 

Conductor, To Short-Circuit a 

To shunt a conductor with a circuit of com- 
paratively small resistance^ 

Conductor, Underground An elec- 
tric conductor placed underground by actual 
burial or by passing it through underground 
conduits or subways. 

Underground conductors, though less unsightly 
than the ordinary aerial conductors, require to 
be laid with unusual care to render them equally 
safe, since, when contacts do occur, all the wires 
in the same conduit are apt to be simultaneously 
affected, thus spreading the danger in many dif- 
ferent directions. They are, however, less liable to 
dangers arising from occasional accidental crosses 
or contacts. 

Conductors, Service — Conductors 

employed in systems of incandescent lighting 
connected to the street mains and to the 
electric apparatus placed in the separate 
buildings or areas to be lighted. 

Conduit, Cement-Lined — A cable 

conduit, the separate ducts of which are sur- 
rounded by any suitable cement. 



Con.] 



123 



[Con. 



Conduit, Handhole of (See Hand- 

hole of Conduit?) 

Conduit, Manhole of (See Man- 
hole of Conduit) 

Conduit, Multiple —A conduit 

formed of concrete or other insulating mate- 
rial, and furnished with a number of separate 
ducts. 

Conduit, Open-Box ■ —A conduit 

consisting of an open box of wood placed in 
a trench and closed with a wooden cover 
after the introduction of the cable. 

Cables or wires may be drawn through such 
conduits in the usual manner. 



-Introducing a 



Conduit, Rodding a — 

wire cr rope into the duct of a closed conduit 
preparatory to drawing the cable through. 

Various methods are in use for rodding a con- 
duit. One much followed consists in using sec- 
tions of gas pipe, the ends of which are furnished 
with screw threads. 

The sections are about four feet in length. One 
section is pushed into the duct at one manhole 
and the successive sections are introduced into 
the duct and screwed onto the section in the duct 
and pushed through until a sufficient length is 
obtained to reach the next manhole, a rope or 
cable is then pulled through from one manhole to 
the next. 

Conduit, Underground Electric 

An underground passageway or space for 
the reception of electric wires or cables. (See 
Subway, Electric) 

Congelation. — The act of freezing, or the 
change of a liquid into a solid on loss of heat, 
or change of pressure. 

Conjugate Coils.— (See Coils, Conjugate) 

Connect. — To place or bring into electric 
contact. 

Connecting. — Placing or bringing into elec- 
tric contact. 

Connection for Intensity. — Connection in 
series. (See Connection, Series) 

This term is now nearly obsolete. 

Connection for Quantity.— Connection in 
multiple. (See Connection, Multiple) 

This term is now nearly obsolete. 



Connection, Mercurial — A form 

of readily adjustable connection obtained by 
providing the poles of one piece of electric 
apparatus with cups or cavities filled with 
mercury, into which the terminals of another 
piece of apparatus are dipped in order to 
place the two in circuit with each other. 

This form of connection is used particularly 
when a very perfect contact or one free from 
friction is desired. 

Connection, Multiple Such a con- 
nection of a number of separate electric 
sources, or electro-receptive devices, or circuits, 
that all the positive terminals are connected 
to one main or positive conductor, and all the 
negative terminals are connected to one main 
or negative conductor. 

In the multiple connection of a number of 
electro-receptive devices, when the devices are 
connected as above described to positive and 
negative leads that are maintained at a constant 
difference of potential, the current passes through 
the devices from one lead to the other by branch- 
ing and flowing through as many separate cir- 
cuits as there are separate receptive devices, 
and the opening or closing of one of these cir- 
cuits does not affect the others. (See Circuits, 
Varieties of. ) 

Connection, Multiple-Series Such 

a connection of a number of separate electric 
sources, or separate electro-receptive de- 
vices, or circuits, that the sources or devices 
are connected in a number of separate groups 
in series, and each of these groups connected 
to main positive and negative conductors or 
leads in multiple arc. (See Circuits, Varie- 
ties of) 

Connection of Battery for Quantity. — 
(See Battery, Connection of , for Quantity) 

Connection of Electric Sources in Cas- 
cade. — (See Cascade, Connection of Electric 
Sources in) 

Connection of Voltaic Cells for Inten- 
sity. — (See Intensity, Connection of Voltaic 
Cells for) 

Connection, Series The connec- 
tion of a number of separate electric 
sources, or electro-receptive devices, or cir- 



Con.] 



124 



[Con, 



cuits, so that the current passes successively 
from the first to the last in the circuit. (See 
Circuits, Varieties of) 

Connection, Series-Multiple Such 

a connection of a number of separate electro- 
receptive devices, that the devices are placed 
in multiple groups or circuits, and these 
separate groups connected with one another 
in series. 

Connection, Telephonic Cross — 

A device employed in systems of telephonic 
communication for the purpose of lessening 
the bad effects of induction, in which equal 
lengths of adjacent parallel wires are alter- 
nately crossed so as to alternately occupy the 
opposite sides of the circuit. 

Connector. — A device for readily con- 
necting or joining the ends of two or more 
wires. (See Post, Binding) 

Connector, Double 
A form of bind- 
ing screw suitable for 
readily connecting two 
wires together. 

A form of double con- 
nector is shown in Fig. 
170. 

Conning 1 Tower. — 
(See Tower, Conning) 

Consequent Points. — (See Points, Conse- 
quent) 

Consequent Poles. — (See Poles, Conse- 
quent.) 

Conservation of Energy. — (See Energy, 
Conservation of) 

Consonance, 'In Consonance." — A term 
employed to express the fact that one simple 
periodic quantity, /. e., 2l wave or vibration, 
agrees in phase with another. 

Constant. — That which remains invariable. 

Constant-Current. — (See Current, Con- 
stant) 

Constant-Current Circuit. — (See Circuit, 
Constant Current) 

Constant-Current, Distribution of Elec- 
tricity by (See Electricity, Distri- 
bution of, by Constant Currents) 



Constant, Dielectric 



-A term some- 




Fig. 1 "jo. Double 
Connector. 



times employed in place of specific inductive 
capacity. (See Capacity, Specific Inductive) 

Constant, Galvanometer — The 

numerical factor connecting the current pass- 
ing through a galvanometer with the deflec- 
tion produced by such current. 

Sometimes a distinction is made between the 
galvanometer constant and the reduction factor, 
the former being used to indicate the relation 
between the current and the geometrical constant 
of the galvanometer, while the latter is used in 
the sense just defined of galvanometer constant. 

Constant Inductance. — (See Inductance, 
Constant) 

Constant Potential. — (See Potential, 
Constant) 

Constant-Potential Circuit. — (See Cir- 
cuit, Constant-Potential) 

Constant, Time, of Electro-Magnet 

— The time required for the magnetizing 



current to rise to the 



of its final value. 



Contact-Breaker, Automatic A 

device for causing an electric current to 
rapidly make and break its own circuit. 

The spring c, Fig. 171, carries an armature of 
soft iron, B, and is 
placed in a circuit in 
such a manner that 
the circuit is closed 
when platinum con- 
tacts placed on the 
ends of D and B, 
touch each other. In 
this case .the arma- 
ture, B, is attracted to 
the core A, of the 
electro- magnet, thus 
breaking the circuit 
and causing the magnet to lose its magnetism. 
The elasticity of the spring C, causes it to fly back 
and again close the contacts, thus again energiz- 
ing the electro-magnet and again attracting B, 
and breaking the circuit. The makes and breaks 
usually follow each other so rapidly as to produce 
a musical note. (See Alarm, Electric.) 

Contact, Dotting An electric con- 




BATTEJ1Y 

Fig. 171. Automatic 
Contact Breaker. 



Con.] 



Ub 



[Con. 



tact obtained by the approach of one con- 
tact point towards another. 

The term dotting contact is used in contradis- 
tinction to a rubbing contact. The rubbing 
contact is generally to be preferred, since it tends 
automatically to remove dust and keep the con- 
tact surfaces polished and free from oxides. 

Contact Dynamo. — (See Dynamo, Con- 
tact^ 

Contact Electricity. — (See Electricity, 
Contact?) 

Contact, Fire-Alarm A contact so 

arranged that an alarm is given when any 
predetermined temperature is reached. 

Fire-alarm contacts are generally operated by 
the expansion of a metal or of a conducting fluid, 
such as mercury. (See Thermostat.) 

Contact Force. — (See Force, Contact?) 

Contact, Full-Metallic A contact, 

which from its small resistance establishes a 
good or complete connection. (See Contact, 
Metallic?) 

Contact, Intermittent The occa- 
sional contact of a telegraphic or other line 
with other wires or conductors by swing- 
ing, or by alternate contraction or expansion 
under changes of temperature. 

Contact, Metallic A contact of 

a metallic conductor produced by its coming 
into firm connection with another metallic 
conductor. 

Contact, Partial A contact of a 

telegraphic, or other line, arising from defect- 
ive insulation, bad earths, or connection with 
an imperfect conductor. 

Contact, Rolling A contact con- 
nected with one part of an electric circuit, 
that completes the circuit by being rolled over 
a conductor connected with and forming 
another part of the circuit. 

Rolling contacts are employed on electric rail- 
roads. (See Railroad, Electric.) 

Contact, Rubbing —A contact 

effected by means of a rubbing motion. 

Contact Series.— (See Series, Contact^ 

Contact, Sliding A contact con- 
nected with one part of a circuit that closes 



or completes an electric circuit by being slid 
over a conductor connected with another 
part of the circuit. 

Sliding contacts are employed in electric rail- 
roads, in rheostats, switches, and a variety of other 
apparatus. (See Railroad, Electric. Rheostat. 
Key, Discharge.) 

Contact, Spring — A spring-sup- 
ported contact connected with one part of a 
circuit that completes said circuit by being 
moved so as to touch another contact con- 
nected with the other part of the circuit. 

The movement required to bring the two con- 
tacts together may be non-automatic, as in the case 
of a push-button, or automatic, as in the case of 
a thermostat. (See Button, Push. Thermostat.) 

Contact Theory of Toltaic Cell.— (See 
Cell, Voltaic, Co?itact Theory of ?) 

Contact, Vibrating A spring con- 
tact, connected with one part of a circuit and 
so supported as to be able to vibrate towards 
and from another contact connected with 
another part of the circuit, thus automatically 
closing and opening said circuit. 

A vibrating contact is used in the automatic 
contact-breaker in which the movement of an 
armature towards an electro-magnet is caused to 
break the circuit of the coils of the electro-magnet, 
and, on its movement away from the magnet, to 
close another contact which again completes the 
circuit of the electro-magnet. (See Contact 
Breaker, Automatic.) 

Contact, Wiping —A contact ob- 
tained by a wiping movement of one con- 
ductor against another. 

The spark for electrically igniting a gas jet is 
obtained by means of a wiping contact of a spring 
moved by the motion of the pendant. (See 
Burner, Plain-Pendant Electric. ) 

Contacts. — A variety of faults occasioned 
by the accidental contact of a circuit with any 
conducting body. 

The word contacts as employed above is in the 
sense of accidental contacts as distinguished from 
predetermined contacts. 

Contacts of an accidental character are of the 
following varieties, viz.: 

(i.) Full, or metallic, as when the circuit is 



Con. 



126 



[Con. 



accidentally placed in firm connection with an. 
other metallic circuit. 

(2.) Partial, as by imperfect conductors being 
placed across wires, or bad earths, or defective 
insulation. 

(3.) Intermittent, as by occasional contacts of 
swinging wires, etc. 

Contacts, Burglar • Alarm Con- 
tacts fitted to windows, doors, tills, steps, 
floors, etc., so that a movement of the parts 
from their natural position gives an alarm by 
sounding a conveniently located bell. 

Contacts, Lamp Metallic plates or 

rings connected with the terminals of an incan- 
descent lamp tor ready connection with the line. 

Contacts, Mercurial Electric con- 
tacts that are opened or closed by the ex- 
pansion or contraction of a mercury column. 

In the commonest forms of mercurial con- 
tacts, on the expansion of the mercury by heat it 
reaches a contact point placed in the tube, and 
thus completes the circuit through it own mass. 

Or, on contraction it breaks a contact, and thus 
disturbing an electric balance, sounds an alarm. 

Continental Code Telegraphic Alphabet. 

— (See Alphabet, Telegraphic, International 
Code) 

Continuity of Current. — (See Current, 
Continuous) 

Continuous Current. — (See Current, Con- 
tinuous) 

Continuous Current, Distribution of 
Electricity by (See Electricity, Dis- 
tribution of, by Constant Currents) 

Continuous Current, Dynamo-Electric 
Machine (See Machine, Dynamo- 
Electric, Continuous Current) 

Continuous-Sounding Electric Bell. — 
(See Bell, Continuous-Sounding Electric) 

Continuous Wires or Conductors. — (See 
Wires or Conductors, Continuous) 

Contraction, Anodic Closure — The 

muscular contraction observed on the closing 
of a voltaic circuit, the anode of which is placed 
over a nerve, and the kathode at some other 
part of the body. 

This term is generally written A. C. C. 



Contraction, Anodic Duration 

The length of time the muscle continues in 
contraction on the opening or closing of a 
circuit, the anode of which is placed over the 
part contracted. 

This term is generally written A. D. C. 

Contraction, Anodic Opening 

The muscular contraction observed on the 
opening of a voltaic circuit, the anode of which 
is placed over a nerve, and the kathode at 
some other part of the body. 

This term is generally written A. O. C. 

When the anode is placed over a nerve and a 
weak current is employed, if the circuit be kept 
closed tor a few minutes, it will be noticed that, 
on opening the circuit the contraction will be 
much greater than if it had been opened after 
being closed for only a few seconds. The effect 
of the A. O. C. therefore depends not only on the- 
current strength, but also on the time during 
which the current has passed through the nerve. 

Contraction of Lines of Magnetic Force. 

— (See Force, Magnetic, Contraction of 
Lines of) 

Contractures. — In electro-therapeutics, 
prolonged muscular spasms, or tetanus, caused 
by the passage of electric currents. 

Contraplex Telegraphy. — (See Telegra- 
phy, Contraplex) 

Controlled Clock.— (See Clock, Electric) 

Controller. — A magnet, in the Thomson- 
Houston system of automatic regulation,, 
whose coils are traversed by the main cur- 
rent, and by means of which the regulator 
magnet is automatically thrown into or out of 
the main circuit on changes in the strength 
of the current passing. (See Regulation, 
Automatic) 

Controlling Clock. — (See Clock, Electric) 

Controlling Magnet. — (See Magnet, Con- 
trolling) 

Convection Currents.— (See Currents,Con- 
vection) 

Convection, Electric The air par- 
ticles, or air streams, which are thrown off 
from the pointed ends of a charged, insulated 
conductor. 



Con.] 



127 



[Cop. 



Convection streams, like currents flowing 
through conductors, act magnetically, and are 
themselves acted on by magnets*. The same thing 
is true of the brush discharge, of the voltaic arc, 
and of convective discharges in vacuum tubes. 

Convection, Electrolytic A term 

proposed by Helmholtz to explain the appa- 
rent conduction of electricity by an electro- 
lyte, without consequent decomposition. 

Helmholtz assumes that the atoms of oxygen or 
hydrogen, adhering to the electrodes during elec- 
trolysis, are mechanically dislodged and diffused 
through the liquid, thus carrying off the elec- 
tricity by the charges received while in contact 
with the electrodes. 

ConYection of Heat, Electric (See 

Heat, Electric Convection of.) 

Convection Streams. — (See Streams, Con- 
vection.) 

Conyective Discharge. — (See Discharge, 
Convective) 

Conversion, Efficiency of, of Dynamo 

— The total electric energy developed by a 
dynamo, divided by the total mechanical 
energy required to drive the dynamo. (See 
Co-efficient, Economic, of a Dynamo-Electric 
Machine) 

The efficiency of conversion 

W + w _ W-f w 

= M W + w + m, 

where W, equals the useful or available electrical 
energy, M, the total mechanical energy, w, the 
electrical energy absorbed by the machine, and 
m, the stray power, or the power lost in friction, 
eddy currents, air friction, etc. 

Converted Currents. — (See Currents, 
Converted) 

Converter. — The inverted induction coil 
employed in systems of distribution by means 
of alternating currents. 

A term sometimes used instead of trans- 
former. (See Transformer) 

Converter, Closed-Iron Circuit 

A closed-iron circuit transformer. (See 
Transformer, Closed-Iron Circuit) 

Converter, Constant-Current — 

A constant-current transformer. (See Trans- 
former, Co?istant-Current) 



Converter, Efficiency of The effi- 
ciency of a transformer. (See Transformer, 
Efficiency of) 

Converter Fuse. — (See Fuse, Converter) 

Converter, Hedgehog* A form of 

transformer. (See Transformer, Hedgehog) 

Converter, Multiple — A multiple 

transformer. (See Transformer, Multiple) 

Converter, Open-Iron-Circuit An 

open-iron-circuit transformer. (See Trans- 
for?ner, Op en- Iron-Circuit) 

Converter, Series A series trans- 
former. (See Transformer, Series) 

Converter, Step-down A step-down 

transformer. (See Transformer, Step-down) 

Converter, Step-up —A step-up 

transformer. (See Transfomier, Step-up) 

Converter, Welding — A welding 

transformer. (See Transformer, Welding) 

Converting Currents.— (See Currents, 
Converting) 

Cooling Box of Hydro-Electric Machine. 
— (See Box, Cooling, of Hydro-Electric 
Machine) 

Co-ordinates, Axes of The axes of 

abscissas and ordinates. 

The two straight lines, usually perpendicular 
to each other, to which distances representing" 
values are referred for the graphic represen- 
tation of such values. (See Abscissas, Axes of) 

Copper Bath.— (See Bath, Copper) 
Copper Plating. — (See Plating, Copper) 
Copper Ribbon. — A variety of strap cop- 
per. (See Copper, Strap) 

Copper, Strap Copper conductors 

in the form of straps or flat bars. 

Strap copper is used on the armatures of some 
dynamos. Heavy copper conductors for such 
purposes are divided into strap copper so as to 
avoid eddy currents. The straps are placed 
alongside one another and insulated by a coating 
of varnish. 

Copper Wire, Hard-Drawn (See 

Wire, Copper, Hard-Drawn) 

Copper Wire, Soft-Drawn — (See 

Wire, Copper, Soft-Drawn) 



Cop.] 



128 



[Cor. 



Copper Voltameter.— (See Voltameter, 
'Copper.) 

Coppered Plumbago— (See Plumbago, 
Coppered?) 

Coppering, Electro Electro-plating 

with copper. (See Plating, Electro) 

Cord- Adjuster. — (See Adjuster, Cord?) 

Cord, Conducting" A small flexible 

cable, usually containing several conductors 
separated from one another by insulating ma- 
terial. 

Cord, Electric A flexible, insulated 

electric conductor, generally containing at least 
two parallel wires. 

Electric cords are named from the purposes for 
which they are employed, battery cords, dental 
cords, lamp cords, motor cords, switch cords, etc. 




Fig. 172. Flexible Cord. 

A two-conductor flexible cord, in which each 
cord is composed of a number of bare copper wires 
placed parallel to and in contact with one another, 
is shown in Fig. 172. The several separate wires 
give flexibility to the cord. 

Cord, Pendant A flexible conductor 

provided for conveying the current to a hang- 
ing electric lamp supported by it. 

Cords, Telephone Flexible con- 
ductors for use in connection with a tele- 
phone. 




Fig. 173. Telephone Cords. 

Telephone cords, attached to an articulating 
telephone, are shown in Fig. 173. 



Core, Armature, Filamentous 

An armature core, the iron of which consists 
of wire. 

Core, Armature, H An armature 

core in the shape of the letter H, generally 
known as the shuttle armature, and some- 
times as the girder armature. 

This form is also called an I armature. 

The H armature core was the form originally 
given to the Siemens armature. In this form a 
single coil of wire was secured on the cross-bar 
of the H armature core, so as to fill up the entire 
space inside the letter, and the ends of the wire 
connected to a two-part commutator, 

Core, Armature, Lamination of 

The subdivision of the core of the armature 
of a dynamo-electric machine into separate 
insulated plates or strips for the purpose of 
avoiding eddy or Foucault currents. 

This lamination must always be perpendicular 
to the direction of the eddy currents that would 
otherwise be produced. (See Currents, Eddy.) 

Core, Armature, of Dynamo-Electric 

Machine The iron core, on, or around 

which, the armature coils of a dynamo-electric 
machine are wound or placed. 

The armature core is laminated for the pur- 
pose of avoiding the formation of eddy or Fou- 
cault currents. 

In drum, and in ring-armatures, the laminae 
should be m the form of thin insulated discs or 
plates of soft iron ; in pole-armatures they should 
be in the form of bundles of insulated wires. 

The iron in the cores should be of such an area 
of cross-section, as not to be readily oversaturated. 

Core, Armature, Radially-Laminated 

An armature core, the iron of which 

consists of thin iron washers. 

Core, Armature, Ribbed A cylin- 
drical armature core provided with longi- 
tudinal projections or ribs that serve as 
spaced channels or grooves for the reception 
of the armature coils. 

Core, Armature, Tangentially-Laminated 

— An armature core, the iron of which 

consists of a coiled ribbon. 

Core, Armature, Ventilation of 

Means for passing air through the armature 



Cor.] 



129 



[Con. 



cores of dynamo-electric machines in order to 
prevent undue accumulation of heat. 

A properly proportioned dynamo-armature 
may need no ventilation, since in such the 
amount of heat generated is small as compared 
with the extent of the radiating surface. 

Since, however, in practice all armatures tend 
to heat at full load, especially in certain installa- 
tions in heated situations, ventilation of the ar- 
mature is desirable. 

Core, Closed-Magnetic — A mag- 
netic core so shaped as to provide a complete 
iron path or circuit for the lines of magnetic 
force of its field. 

Core, Laminated A core of iron 

which -has been divided or laminated, in order 
to avoid the injurious production of Foucault 
or eddy currents. 



Core, Lamination of 



— Structural 



subdivisions of the cores of magnets, arma- 
tures, and pole-pieces of dynamo-electric 
machines, electric motors, or similar appa- 
ratus, in order to prevent heating and subse- 
quent loss of energy from the production of 
local, eddy or Foucault currents. 

These laminations are obtained by forming the 
cores of sheets, rods, plates, or wires of iron in- 
sulated from one another. 

The cores of dynamo-electric machine arma- 
tures should be subdivided in planes at right 
angles to the armature coils; or in planes parallel 
to the direction of the lines of force and to the 
motion of the armature; cr, in general, in planes 
perpendicular to the currents that would otherwise 
be generated in them. 

Pole pieces should be divided in planes per- 
pendicular to the direction of the currents in the 
armature wires. 

Magnet cores should be divided in planes at 
right angles to the magnetizing current. 

Core of Cal)le.— The conducting wires of 
an electric cable. (See Cable, Electric^ 

Core, Open-Magnetic Any mag- 
netic core so shaped that the lines of magnetic 
force of its field complete their circuit partly 
through iron and partly through air. 

Core Ratio of Cal)le.— (See Cable, Core 
Ratio of.) 



Core, Ring A hollow, cylindrical 

core of short length. 

Core, Ring-, Elongated A hollow, 

cylindrical core of comparatively great length. 

Core, Solenoid A core so arranged 

as to be drawn into a solenoid on the passage 
of the current through its coils, and to be 
withdrawn therefrom, on the stopping of the 
current by the action of a spring or weight. 
(See Solenoid.) 

Core, Stranded, of Cable The 

conducting wire or core of a cable formed of 
a number of separate conductors or wires in- 
stead of a single conductor of the same weight 
per foot as the combined conductors. 

Core Transformer. — (See Transformer, 
Core. ) 

Cored Carbons. — (See Carbons, Cored.) 

Cored Electrodes. — (See Electrodes, 
Cored.) 

Corona?, Auroral A crown-shaped 

appearance, sometimes assumed by the auro- 
ral light. (See Atirora Borealis.) 

Corposant. — A name sometimes given by 
sailors to a St. Elmo's Fire. (See Fire, St. 
Elmo's.) 

Correlation of Energy. — (See Energy, 
Correlation of.) 

Corresponding Points. — (See Points, Cor- 
responding.) 

Cosine. — One of the trigonometrical func- 
tions. (See Trigonometry.) 

Cotangent. — One of the trigonometrical 
functions. (See Trigonometry.) 

Coulomb. — The unit of electrical quantity. 

A definite quantity or amount of the thing 
or effect called electricity. 

Such a quantity of electricity as would pass 
in one second in a circuit whose resistance is 
one ohm, under an electromotive force of 
one volt. 

The quantity of electricity contained in a 
condenser of one farad capacity, when sub- 
jected to an electromotive force of one volt. 

The quantity of electricity that flows per 
second past a cross-section of a conductor 



Coil] 



130 



[Cou. 



conveying an ampere.— {Ayrton.) (See Am- 
pere. Farad. Volt.) 

Coulomb's Torsion Balance. — (See Bal- 
ance, CoulojnVs Torsion) 

Coulomb-Volt. — A Joule, or .7373 foot- 
pound. 

The term is generally written volt-coulomb. 
(See Volt -Coulomb.) 

Counter, Electric A device for 

counting and registering such quantities as 
the number of fares collected, gallons of water 
pumped, sheets of paper printed, revolutions 
of an engine per second, votes polled, etc. 

Various electric devices are employed for this 
purpose. They are generally electro-magnetic 
in character. 

Counter-Electromotive Force. — (See 
Force, Electromotive, Counter I) 

Counter Electromotive Force Lightning 1 
Arrester. — (See Arrester, Lightning, Coun- 
ter-Electromotive Force) 

Counter-Electromotive Force of Convec- 
tive Discharge. — (See Force, Electro?notive, 
Counter, of Convective Discharge) 

Counter-Electromotive Force of Mutual 
Induction. — (See Force, Electromotive, 
Counter, of Mutual Induction) 

Counter-Electromotive Force of Self-in- 
duction. — (See Force, Electromotive, Coun- 
ter, of Self-induction) 

Counter-Electromotive Force of Self-in- 
duction of the Primary. — (See Force, 
Electromotive, Counter, of Self-induction of 
the Primary) 

Counter-Electromotive Force of Self-In- 
duction of the Secondary. — (See Force, 
Electromotive, Counter, of Self-induction of 
the Secondary) 

Counter-Electromotive Force of the 
Primary. — (See Force, Electromotive , 
Counter, of the Primary) 

Counter Inductive Effect— (See Effect, 
Counter Inductive) 

Couple. — In mechanics, two equal parallel 
forces acting in opposite directions but not in 
the same line, and tending to cause rotation. 

The moment, or effective power of a couple, is 



equal to the intensity of one of the forces multiplied 
by the perpendicular distance between the direc- 
tions of the two forces. 

Couple, Astatic — Two magnets of 

exactly equal strength so placed one over the 
other in the same vertical plane as to com- 
pletely neutralize each other. 

An astatic couple has no directive tendency. A 
pair of magnets combined as an astatic couple is 
called an astatic needle. (See Needle, Astatic.) 

Couple, Magnetic The couple which 

tends to turn a magnetic needle, placed in the 
earth's field, into the plane of the magnetic 
meridian. 

If a magnetic needle is in any other position 
than in the magnetic meridian, there will be two 
parallel and equal forces acting at A and B, Fig. 
174, in the directions shown by the arrows. 
Their effect will be to ro- 
tate the needle until it 
comes to rest in the mag- 
netic meridian N S. 

The total force acting 
on either pole of a needle 
free to move in any direc- 
tion, is equal to the 
strength of that pole mul- 
tiplied by the total inten- 
sity of the earth's field at 
that place ; or, if free to move in a horizontal 
direction only, is equal to the intensity of the 
earth's horizontal component of magnetism at 
that place, multiplied by the strength of that pole. 

The effective power or moment of a magnetic 
couple is equal to the force exerted on one of the 
poles multiplied by the perpendicular distance, 
P Q, between their directions. 

Couple, Moment of The effective 

power or force of a couple. 

The moment of a couple is equal to the inten- 
sity of one of the forces multiplied by the perpen- 
dicular distance between the direction of the 
forces. 

Couple, Thermo-Electric Two dis- 
similar metals which, when connected at their 
ends only, so as to form a completed electric 
circuit, will produce a difference of potential, 
and hence an electric current, when one of the 
ends is heated more than the other. 

Thus if a bar of bismuth be soldered to a bar 




Fig. 174. Magnetic 
Couple. 



•Cou.] 



131 



[Cre. 



of antimony the combination will form a thermo- 
electric couple, and the circuit so formed will 
have a current passing through it when one junc- 
tion is hotter or colder than the other. 

There is, according to Lodge, a true contact 
force, at a thermo-electric junction, asis shown by 
the reversible heat effects produced when an 
electric current is passed across such junction; for, 
in one direction more heat is produced, and in the 
opposite direction less heat. This, as is well 
known, differs from the irreversible heat produced 
by a current through a homogeneous metallic 
conductor. The reversible heat effects, or as they 
are called the Peltier effects, may overpower and 
conceal the heating effects. But, in addition to 
these effects, since a difference of potential, calh d 
;a Thomson effect, exists in a substance unequally 
heated, currents are so produced, and these are 
also influential in causing the difference of poten- 
tial of a thermo-electric couple. 

" There are then/' says Lodge, "in a simple 
circuit of two metals with their junctions at differ- 
ent temperatures, altogether four E. M. Fs., one 
in each metal, from hot to cold, or vice versa, and 
one at each junction, and the current which flows 
. around such a circuit is propelled by the resultant 
of these four." * * * "These four forces, 
two Thomson forces in the metals, and two Peltier 
forces at their junctions, may some of them help 
and some hinder the current." * * * "When- 
ever they help, the locality is to that extent cooled ; 
whenever they hinder, it is to that extent 
warmed." 

The action of a thermo-electric couple in pro- 
ducing a difference of potential is therefore a 
complicated one, and depends on Peltier and 
Thomson effects, as well as on the thermo-electric 
effect. (See Effect, Peltier. Effect, Thomson. 
Effect, Thermo-Electric.) 

Conple, Yoltaic Two materials, 

usually two dissimilar metals, capable of 
acting as an electric source when dipped in 
an electrolyte, or capable of producing a 
difference of electric potential by mere con- 
tact. 

Liquids and gases are capable of acting as 
voltaic couples. 

All voltaic cells have two metals, or a metal and 
a metalloid, or two gaseous or liquid substances 
which are of such a character that, when dipped 
into the exciting fluid one only is chemically 
acted on. 



Each one of these two substances is called an 
ele??ient of the cell, and the two taken collectively 
form a voltaic couple. 

The elements of a voltaic couple may consist of 
two gases or two liquids. (See Battery, Gas.) 

Coupled Cells.— (See Cells, Coupled) 

Coupler, Yoltaic Any device by 

means of which voltaic cells may be readily 
coupled or connected in different forms of 
circuits. (See Circuits, Varieties of) 

Coupling" of Yoltaic Cells or Other 
Electric Sources. — A term indicating the 
manner in which a number of separate 
electric sources may be connected so as to 
form a single source. (See Circuits, Varie- 
ties of) 

Cramp, Telegrapher's An affec- 
tion of the hand of a telegrapher due to im- 
moderate and excessive use of the same 
muscles, somewhat similar to the disease 
known as writer's cramp. 

Telegrapher's cramp, like writer's cramp, may 
be defined as a professional neurosis of co-ordina- 
tion. It appears not only in certain groups of 
muscles, but is limited to such groups, only when 
they are performing certain complicated opera- 
tions. For example, telegrapher's cramp is 
practically a paralysis of certain muscles of the 
hand and wrist of the operator. These muscles, 
when called on to perform the somewhat delicate 
movements required in sending a telegraphic dis- 
patch, are incapable of performing their proper 
functions, but when calle 1 on to perform in part 
other similar actions, provided all these actions 
are not required to be used, appear to be un- 
affected. 

The ability of the operator to send with either 
hand would lessen the liability to this disease. 

Crater in Positive Carbon. — A depression 
at the end of the positive carbon of an arc 
lamp which appears when a voltaic arc is 
formed. (See Arc, Voltaic) 

Creep, Diffusion The .flow of an 

electric current in portions of a conducting 
substance, outside the parts that lie in the 
direct lines between the points where the 
terminals of the same are applied to the con- 
ducting substance. 



Cre.] 



132 



[Cro. 



Creeping, Electric A term some- 
times applied to the creeping of a current. 
(See Current, Creeping of) 

Creeping' in Voltaic Cell. — (See Cell, Vol- 
taic, Creeping in.) 

Creeping of Current. — (See Current, 
Creeping of, Electric) 

Creeping-, Saline The formation 

of salts by efflorescence on the walls of a solid 
immersed in a solution of a salt. 

Creosoting. — A process employed for the 
preservation of wood, as, for example, tele- 
graph poles, by injecting creosote into the 
pores of the wood. (See Pole, Telegraphic) 

Critli. — A term proposed by A. W. Hoff- 
man, as a unit of weight, or the weight of 
one litre, or cubic decimetre, of hydrogen at 
O C. and 760 mm. barometric pressure. 

Critical Current. — (See Current, Crit- 
ical) 

Critical Current of a Dynamo. — (See 
Current, Critical, of a Dynamo) 

Critical Distance of Lateral Discharge 
through Alternative Path. — (See Distance, 
Critical, of Lateral Discharge through 
an Alternative Path) 

Critical Speed of Compound-Wound Dy- 
namo. — (See Speed, Critical, of Compound- 
Wound Dynamo) 

Crookes' Dark Space. — (See Space, Dark, 
Crookes') 

Crookes' Electric Radiometer. — (See Ra- 
diometer, Electric, Crookes '.) 

Cross Arm. — (See Arm, Cross) 

Cross-Connecting Board. — (See Board, 
Cross- Con 11 ecting) 

Cross, Electric A connection, gen- 
erally metallic, accidentally established be- 
tween two conducting lines. 

A defect in a telegraph, telephone or other 
circuit caused by two wires coming into 
contact by crossing each other. 

A swinging or intermittent cross is caused by 
wires, which are too slack, being occasionaly 
blown into contact by the wind. 



A weather cross arises from defective action oi 
the insulators in wet weather. 

Cross, Swinging or Intermittent 

An accidental contact, generally metallic, 
caused by wires being brought into occasional- 
contact with one another, or with some other 
conductor, by the intermittent action of the: 
wind. 

Cross, Weather A contact or leak 

occurring in a telegraphic or other line dur- 
ing wet weather, from the defective action of 
the insulators. 

Crossing Cleat— (See Cleat, Crossing) 

Crossing, Live-Trolley A device 

whereby a trolley moving over a line that 
crosses a second line at an angle is enabled 
to maintain its electrical connection with the 
line while crossing. 

A live-trolley crossing is necessitated where one- 
line of electric railway crosses another. The 
upper line must, of course, provide a space or 
opening for crossing the lower line at the points; 
of intersection. This is effected in the Bagnall 
live-trolley crossing, shown in Fig. 175, by attach- 



Fig. 175. Live- Trolley Crossing. 

ing to the upper trolley wire a bridge piece of 
light lathe casting, provided at its centre with a. 
gap through which the trolley wire passes. This- 
bridge piece is insulated from the trolley wire by 
means of a disc of insulating material at the cen- 
tre of the bridge, which is provided with a hinged 
curved lever, that in its normal position rests un- 
der the influence of gravity in the position shown 
in the figure. The passage of the trolley wheel 
along the wire carries the line under it and thus- 
bridges the gap, as shown by the position of the 
dotted lines. 

Crossing Wires. — (See Wires, Crossing) 

Cross-Over Block.— (See Block, Cross- 
Over) 

Cross-Over, Trolley A device by 

means of which a trolley is enabled to pass 
over the points where different lines cross one 
another without serious interruption. 



Cro.] 133 

A trolley cross-over, for trolley lines, is shown 
in Fig. 176. 



[Cur. 




Fig. 1/6. Trolley Cross Over. 

Crow-foot Zinc. — (See Zinc, Crow-foot?) 

Crucible, Electric A crucible in 

which the heat of the voltaic arc, or of elec 
trie incandescence, is employed either to per- 
form difficult fusions ; or for the purpose of 
effecting the reduction of metals from their 
ores or the formation of alloys. (See Fur- 
nace, Electric?) 

Crystal —A solid body bounded by sym- 
metrically disposed plane surfaces 

A definite form or shape is as characteristic of 
an inorganic crystalline substance as it is of an 
animal or plant. Each substance has a form in 
which it generally occurs. There are, however, 
certain modifications of the typical forms which 
cause plane surfaces to appear curved, and the 
Symmetrical arrangement of the face^ to disap 
pear. These modifications often render it ex 
tremely difficult to recognize the true typical 
form 

For the different fundamental crystalline forms. 
or systems of crystals, see any standard work on 
chemistry. 

Crystal, Hemihedral —A crystal 

whose shape or form has been modified by 
the replacement of half its edges or solid 
angles, 

A hemihedral crystal possesses different forms 
at the ends or extremities of its axes. Hemi- 
hedral crystals, when unequally heated, develop 
electrical charges. 

Electricity produced in this way was formerly 
called pyro-electricity. (See Electricity, Pyro.) 

Crystal, Holohedral —A crystal 

whose shape or form has been modified by 
the replacement of all its edges or solid 
angles. 

Crystalline Electro-Metallurgical De- 
posit.— (See Deposit. Crystalline, Electro- 
Met a llurgical.) 

Crystallization.— Solidification from a state 
of solution or fusion in a definite crystalline 
form. 



The crystallization of a dissolved solid is fa- 
vored by any cause that gives increased freedom 
of movement to its molecules, such for example as 
solution, fusion, sublimation, or precipitation 

Crystallization by Electrolytical Decom- 
position. — The crystalline deposition of vari- 
ous metals by the passage of an electric cur- 
rent through solutions of their salts under 
certain conditions. 

A strip of zinc immersed in a solution of sugar 
of lead (acetate of lead) soon becomes covered 
with bright metallic plates of lead, that are elec- 
trolytically deposited by the weak currents due to 
minute voltaic couples formed with the zinc by 
particles of iron, carbon, or other impurities in 
the zinc. The deposit assumes at times a tree- 
like growth, and is therefore called a lead tree. 
(See Couple, Voltaic.) 

Crystallization, Electro Crystalli- 
zation effected during electrolytic deposition. 

Crystallize. — To separate from a liquid 
or vapor, in the form of a crystalline solid. 

Crystalloid. — Those portions of a mixed 
substance subjected to dialysis, that are capa- 
ble of crystallization. (See Dialysis?) 

Cube, Faraday's —An insulated 

room cubic in shape, covered on the inside 
with tin foil, which, when charged on the 
outside gives no indications to an observer on 
the inside, though furnished with delicate in- 
struments, 

Faraday's cube illustrates the fact that an elec- 
trostatic charge resides on the outside of an insu- 
lated conductor. (See Net, Faraday s.) 

Cup, Mercury A cup or cavity 

filled with mercury and connected with the 
pole of an electric apparatus for the ready 
placing of the same in circuit with other elec- 
tric apparatus. 

To connect apparatus it is only necessary to 
insert the free terminal of one apparatus in the 
mercury cup of the other. 

Cup. Porous A porous cell. (See 

Cell, Porous?) 

Curb, Double A device for in- 
creasing the speed of signaling, by means of 
which the line is rid of its charge before the 
next signal is sent, by sending an opposite 
charge, then another in the same direction,. 



Cur.] 



134 



LCur. 



then finally another in the same direction 
before connecting with the ground. 

The effect of the third charge is to reduce the 
potential of the line more nearly to zero at the 
end of the signal. 

Curb, Single — A device for in- 
creasing the speed of signaling telegraphic- 
ally by ridding the line of its previous charge 
by sending a reversed current through it be- 
fore connecting with the ground. 

In single-curb signaling the operator in dis- 
charging the line before sending another signal 
through it, before putting the line to earth, re- 
verses the battery, and then connects to earth. 

Current, Absolute Unit of A cur- 
rent of 10 amperes. (See Ampere. Units, 
Practical.) 

A current of such a strength that when 
passed through a circuit of a centimetre in 
length bent in the form of an arc of a circle 
one centimetre in radius, will act with the 
force of a dyne on a magnetic pole of unit 
strength, placed at the centre of the arc. 

The ampere, the practical unit of current, is 
but -jL the value of the absolute unit of current. 

Current, Action of, on a Magnetic Pole 

An attraction or repulsion depend- 



ents in a certain direction, are indicated by 
values above a horizontal line, and negative elec 
tromotive forces, by values below the line. 

The curves ABC, and C D E, Fig. 177, are 



ent on the name of the pole and the direction 
of the current. 

Two currents of electricity attract or repel each 
other according to the direction in which they 
are flowing, and the mutual positions of their 
circuits. A current and a magnetic pole exert an 
action on each other which, strictly speaking, is 
neither attraction nor repulsion, but which is ro- 
tation, that may, however, be regarded as being 
produced by the combined action of attraction 
and repulsion. 

Current, Alternating- A current 

which flows alternately in opposite directions. 

A current whose direction is rapidly re- 
versed. 

The non-commuted currents generated by the 
differences of potential in the armature of a 
dynamo-electric machine are alternating or 
simple-periodic-currents. 

In a characteristic curve of the electromotive 
forces of alternating currents, positive electro- 
motive forces, or those that would produce cur- 



ill! 

\\ i i 


!ri!!\ 




A 


c\lj 


!iii!|i E 

J i i W 



Fig, 177. Curve of Electromotive Forces of Alternating 
Currents. 

often called phases, and represent the alternate 
phases of the current. 

Current, Alternative —A voltaic 

alternative. (See Alternatives, Voltaic^) 
Current, Assumed Direction of Flow 

of The direction the current is as- 
sumed to take, i. e., from the positive pole of 
the source through the circuit to the negative 
pole of the source. 

The electricity is assumed to come out of the 
source at its positive pole, and to return or flow 
back into the source at its negative pole. This 
convention as to the direction of the electric cur- 
rent is in accordance with the assumption of the 
direction of flow of lines of magnetic forces. 

The oldidea'of a dual or double current flowing 
in opposite directions is still maintained by some, 
(See Force, Lines of, Direction of.) 

Current, Axial — In electro-thera- 
peutics a current flowing in a nerve in the 
opposite direction to the normal impulse in 
the nerve. 

Current. Break-Induced The cur- 
rent induced by a current in its own, or in 
another circuit, on breaking or opening the 
same. 

The current induced in the secondary on 
the breaking of the primary circuit. 

The break-induced current set up by a current 
in its own circuit is sometimes called the direct- 
induced current. 

Lord Rayleigh has shown that within, certain 
limits the break-induced current has a greater 
effect in magnetizing steel needles, the smaller 
the number of turns of wire in the secondary. In 



Cur.l 



135 



[Cur. 



the case of a galvanometer, it is well known that 
the opposite is true. The deflection of the gal- 
vanometer needle depends on the strength of the 
whole current. The magnetizing power depends, 
for the greater part, on the strength of the cur- 
rent at the beginning of its formation 

Current Closed-Circular A cur- 
rent flowing in a circular circuit. 

A small closed -circular current may be replaced 
magnetically by a thin disc of steel, magnetized in 
a direction perpendicular to its iace, and the edge 
of which corresponds to the edge of the circular 
conductor. 

Current-Conimiiter. — (See Commuter, 
Current?) 

Current. Conduction —The current 

that passes through a metallic or other con- 
ducting substance as contradistinguished 
from a current produced in a non-conductor 
or dielectric. (See Current, Displacement^ 

Current, Constant A current that 

continues to flow in the same direction for 
some time without varying in strength. 

This term is sometimes used to mean a con 
tinuous or direct current in coiftradistmction to 
an alternating current, but it ought to be applied 
only to unvarying currents, such, for example as 
a constant current of 10 amperes. 

Current, Continuous — An electric 

current which flows in one and the same 
direction 

Although the term continuous current is used 
as synonymous with constant current, it is not 
entirely so; a continuous current flows constantly 
in the same direction A constant current not 
only flows continuously in the same direction, but 
maintains an approximately constant current 
strength 

This term continuous current is used in the 
opposite sense to alternating current, and in the 
same sense as a direct current. 

Current, Creeping of Electric 

A change in the direction of path of a current 
from the direct line between the points of 
connection with the source. 

When the terminals of any electric source are 
placed in contact with any two points of a metallic 
sheet of conducting material, the flow of the cur- 
rent is not confined to the direct line between the 




points of contact, but creeps or diffuses into por- 
tions of the conducting plate surrounding this 
direct line. (See Current, Diffusion of.) 

In a somewhat similar manner, the current 
is said to creep, or to establish a partial short- 
circuit around the poles of a poorly insulated 
voltaic battery, or other electric source. 

Current, Critical 

— The current at which a 
certain result is reached. 

Current, Critical, of a 

Dynamo That value 

of the current at which the 
characteristic curve begins 
to depart from a nearly 
straight line. — [Silvanus Fig 178 Critical 
P, Thompson) Curve of Dynamo 

Current 

In Fig. 178 the critical 

current is shown in three different cases, as oc- 
curring where the dotted vertical line cuts the 
characteristic curves. 

The speed at which a series dynamo excites 
itself is often called the critical speed. 

Current, Demarcation —A term 

sometimes applied to an electric current ob- 
tained from an injured muscle, 

" Every injury of a muscle or nerve causes at 
the point of injury a dying surface, which behaves 
negatively to the positive intact substance." — 
(LanJois &° Stirling.) 

Current Density.— The current of elec- 
tricity which passes in any part of a circuit as 
compared with the area of cross-section of 
that part of the circuit. 

In a dynamo- electric machine the current den- 
sity in the armature wire should not, according to 
Silvanus P. Thompson, exceed 2.500 amperes 
per square inch of area of transverse section of 
conductor. 

The current density in a dynamo wire, of 
necessity depends on the sectional area of the 
coils. If, for example, a current of 50 amperes 
be safe in an armature section of eight turns it 
may be safely increased to 100 amperes if the 
conductors are cross- sectioned so as to make but 
four turns. — {Urqiiliart.) 

In electro- plating, for every definite current 
strength that passes through the bath, or in other 
words, for a definite number of coulombs, a 
definite weight of metal is deposited, the charac- 



Cur.] 136 [Cur. 1 

ter of which depends on the current density. The stant in direction, as distinguished from an 

character of an electrolytic deposit will therefore alternating current, 

depend on the current density at that part of the A conti n UOU s current, 
circuit where the deposit occurs. 

The following table from Urquhart gives the Current, Direct-lilted The cur- 
practical working value for the current density rent induced in a circuit by induction on it- 
for electro-metallurgical deposits : sel f> or self-induction, on breaking or openb.g 

the circuit. (See Currents, Extra) 

Current Density (or Amperes on This is called, the direct-induced current because 

CATHODE). -j. s dj rec ti on j s j n {i ie same direction as the induc- 
Amperes 

Solution of per square foot. ing current. 

Copper, acid bath 5.0 to 10. Current, Direction of The direc- 

Copper cyanide bath 3.0 « 5.0 i[oR ^ ^^ current ^ assumed to take 

Silver, double cyanide 2.0 ' ( 5.0 , , . , ,. 1 .i_ 

„.,'.,/ ., J out from one pole of any source through the 

Gold, chloride in cyanide 1.0 " 2.0 . . r . . , . . « , 

tvt- i i j ui 1 v. l £ o circuit and its translating devices back to the 

Nickel, double sulphate 6.0 " 8.0 & 

Brass, cyanide 2.0" 3.0 source through its other pole. 

Tin ... Conventionally, the current is assumed to come 

_. . _, ,., , , out from the positive pole cf the source and to go 

Current, Diacritical —Such a , , . ., _ .z. ,. , 

' back to the source at the negative pole. 

strength of the magnetizing current as pro- _ _. , _. 

, & .. ' £ ■ , Current, Displacement The rate 

duces a magnetization of an iron core equal , , ' , 

, ir of change of electric displacement. 

to half-saturation. » , . , , , . 

A brief conduction current produced m a 

The diacritical current is the current which, ,. , , , , . ,. , . /c 

.,,.., , dielectric by an electric displacement, (bee 

flowing through the diacritical number of ampere- _ . , ■_ , _, , . . 

.„ ,? ,, , , . Displacement, Electric A 

turns, will bring up the magnetism produced to * J 

half- saturation. This is called a displacement current in order 

The diacritical number of ampere-turns is such to distinguish it from a conduction current in any 

a number of ampere-turns as would reduce the conductor. 

magnetic permeability to half its full value. The displacement current continues while the 

displacement of electricity is going on. Dis- 

Current, Diffusion of A term em- placeme nt currents have all the properties of con- 

ployed to designate the difference in the duction currents, and, like the latter, produce a 

density of current in different portions of a magnetic field; in fact, they resemble extremely 

conductor. (See Current. Creeping of, Elec- brief conduction currents. 

trie) The difference between conducting substances 

*t ± „,„ . n t,, , ™ and dielectrics, lies in the fact that the conducting 

Current. Diffusion of Electro-Therapeu- , , , , , ,. , 

r substances do not possess an elastic force, en- 

tlc The difference in the density of abUng them to resist e]ectnc dlsplaceme nt. In 

current in different portions of the human other wor ^ Sj conducting substances possess no 

body between the electro-therapeutic elec- electric elasticity, and can have no true displace- 

trodes. ment current established in them. (See Elasti- 

When the electrodes are placed at any two city, Electric) 
given points of the human body, the current A displacement current, like a conduction cur- 
branches through various paths, extending in a rent, possesses a magnetic field, or is encircled by 
general direction from one electrode to the other, lines of magnetic force. (See Field, Magnetic, of 
according to the law of branched or derived cir- an Electric Current.) 

cuits, and flowing in greater amount, or with Current, Electric The quantity of 

greater density of current, through the relatively electricity which passes per second through 

better conducting paths. (See Current Density.) any con d U ctor or circuit. 

This is sometimes called the creeping of the The rate at whkh a definite quantity of elec _. 

current. (See Current, Creeping of) ^^ passes Qr flowg thrQugh & conductor or 

Current, Direct — A current con- circuit. 



€ur.] 



137 



[Cur. 



The ratio existing between the electro- 
motive force, causing the current, and the 
resistance which may, for convenience, be 
regarded as opposing it, expressed in terms 
of quantity of electricity per second. 

The unit of current, or the ampere, is equal to 
one coulomb per second. (See Ampere. Coulomb. ) 

The word current must not be confounded 
with the mere act of flowing; electric current 
signifies rate of flow, and always supposes an 
electromotive force to produce the current, and a 
resistance to oppose it. 

The electric current is assumed to flow out 
from the positive terminal of a source, through 
the circuit and back into the source at the nega- 
tive terminal. It is assumed to flow into the 
positive terminal of an electro-receptive device 
such as a lamp, motor, or storage battery, and 
out of its negative terminal; or, in other words, 
the positive pole of the source is always con- 
nected to the positive terminal of the electro-re- 
ceptive device. 

Professor Lodge draws the following com- 
parison between the motions of ordinary mat- 
ter, heat and electricity: "Consider the modes 
in which water may be made to move from place 
to place; there are only two. It may be pumped 
along pipes, or it may be carried about in jugs. 
In other words, it may travel through matter, or, 
it may travel with matter. Just so it is with heat, 
also. Heat can travel in two ways: it can flow 
through matter, by what is called ' conduction, ' 
or, it can travel with matter, by what is called 
'convection.' There is no other mode of con- 
veyance of heat." * # * "For electricity 
the same is true. Electricity can travel with 
matter, or it can travel through matter, by con- 
vection, or by conduction, and by no other way." 

In the above, the radiation of heat is apparently 
lost sight of. 

In the opinion of some, an electric current con- 
sists of two distinct currents, one of positive and 
the other of negative electricity, flowing in oppo- 
site directions. Each of these currents is supposed 
to be equal in amount to the other. 

The e'.ectric currentis now regarded as passing 
through the dielectric surrounding the conductor, 
rather than through the conductor itself. (See 
Current, Electric, Method of Propagation of, 
Through a Circuit.') 

The current that flows or passes in any circuit 
is, in the case of a constant current, equal to the 



electromotive force, or difference of potential, 
divided by the resistance, as — 

(See Law of Ohm.) 

Current, Electric, Method of Propagation 

of, Through a Circuit When an 

electric current is propagated through a wire 
or other conductor, it is not sent or pushed 
through the conductor, like a fluid through 
a pipe or other conductor, but is, so to speak, 
rained down on the surface of the conductor 
from the medium or dielectric surrounding it. 

Poynting, who has carefully studied this mat- 
ter, remarks as follows, viz.: "A space contain- 
ing electrical currents may be regarded as the 
field where energy is transformed at certain points 
into the electric or magnetic kind, by means of 
batteries, dynamos, thermopiles, etc., and in 
other parts of the field this energy is being again 
transformed into heat, work done by the electro- 
magnetic forces, or any other form yielded by 
currents. 

' ' Formerly the current was regarded as some- 
thing traveling in the conductor, and the energy 
which appeared at any part of the circuit was 
supposed to be conveyed thither through the 
conductor by the current. Bat the existence of in- 
duced currents and electro-magnetic actions have 
led us to look on the medium surrounding the 
conductor as playing a very important part in the 
development of the phenomena. If we believe in 
the continuity of the motion of energy, we are 
forced to conclude that the surrounding medium 
is capable of containing energy, and that it is 
capable of being transferred from point to point. 
We are thus led to consider the problem, how 
does the energy about an electric current pass 
from point to point; by what paths does it travel, 
and according to what laws ? Let us take a spe- 
cific case. Suppose a dynamo at one spot gen- 
erates an electric current, which is made to operate 
an electric motor at a distant place. We have 
here, in the first place, an absorption of energy 
from the prime motor into the dynamo. We find 
the whole space between and around the conduct- 
ing wires magnetized and the seat of electro- 
magnetic energy. We have further a retrans- 
formation of energy in the motor. The question 
which presents itself for solution is to decide how 
the energy taken up by the dynamo is trans- 
mitted to the motor, by what path it travels 



Cur.] 



138 



[Cur. 



and according to what laws ? Briefly stated, the 
tendency of recent views is that this energy is 
conveyed through the electro-magnetic medium 
or ether, and that the function of the wire is to 
localize the direction or to concentrate the flow in 
a particular path, and thus provide a sink or place 
in which the energy can be dissipated. * * * " 

Taking again, for instance, the case of the dis- 
charge of a condenser by a conductor. He says: 
"Before the discharge we know that the energy 
resides in the dielectric, between the conducting 
plates. If these plates are connected by a wire, 
according to these views, the energy is transferred 
outwards along the electrostatic, equipotential sur- 
faces, and moves on to the wire and is there con - 
verted into heat. According to this view we 
must suppose the lines of electrostatic induction, 
running from plate to plate, to move outwards, as 
the dielectric strain lessens, and while still keep- 
ing their ends on the plates, to finally converge 
in on the wire and be there broken up and their 
energy dissipated as heat." 

In other words, some of the energy of the ex- 
panding lines of induction is changed into mag- 
netic energy; this energy is contained in ring- 
shaped tubes of force, which expand outwards 
from between the plates and then contract on 
some other part of the conductor. 

The time of the discharge, then, consists of the 
following steps, viz. : 

(I.) The time during which the energy of the 
charge is nearly all electrostatic and is repre- 
sented by the energy contained in the lines or 
tubes of electrostatic induction, running from 
plate to plate of the condenser. 

(2.) The time during which the discharge is at 
its maximum and the energy consists of two parts, 
viz.: energy associated with the outward ex- 
panding lines of electrostatic induction, and energy 
associated with the closed lines or tubes of mag- 
netic force, which at first are expanding and after- 
wards contracting. 

(3.) The time when the energy has been ab- 
sorbed, or the period in which the energy in the 
wire or the conductor has either been dissipated 
in the form of non-luminous radiation or obscure 
heat. 

(4.) The time during which this non-luminous 
heat gives up its energy again to the surrounding 
medium in the shape of heat waves. 

Current, Electro-Therapeutic Polarizing- 

The current which produces the 



phenomena of electrotonus. (See Electro- 
tonus.) 

Current, Element of — A term 

employed in mathematical discussions to in- 
dicate a very small part of a current for ease 
in considering its action on a magnetic needle 
or other similar body. 

Current, Faradic In electro- 
therapeutics, the current produced by an in- 
duction coil, or by a magneto-electric machine. 

A rapidly alternating current, as distin- 
guished from a uniform voltaic current. 

A voltaic current that is rapidly alternated by 
means of any suitable key or switch is sometimes 
called a voltaic alternative. The discharge from 
a Holtz machine is sometimes called a Franklinic 
Current. (See Alternatives \ Voltaic. Current y 
Franklinic.) 

Current - Filaments. — (See Filament y 
Current?) 

Current, Franklinic A term some- 
times used in electro-therapeutics for a cur- 
rent produced by the action of a frictionaL 
electric machine. 

The term, Franklinic current, is used in con- 
tradistinction to Faradic current, or that produced 
by induction coils, or, in contradistinction to a 
galvanic or voltaic current, or that produced by 
a voltaic battery. 

Current, Generation of, by Dynamo-Elec- 
tric Machine ■ --The difference of 

potential developed in the armature coils 
by the cutting of the lines of magnetic 
force of the field by the coils, during the rota- 
tion of the armature. 

If a loop of wire whose ends are connected to 
the two-part commutator, shown in Fig. 179, be 

A 




Fig. 17 Q. Induction in Armature Looj>. 

rotated in the magnetic field between the magnet 
poles N and S, in the direction of the large arrow, 
differences of potential will be generated which 




Car.] 139 [Cur. 

will cause currents to flow in the direction indi- tation as being near, or at right angles to the di- 

cated by the small arrows during its motion past ameter of greatest average magnetic density, 

the north pole from the top to the bottom, but in the (See Lead, Angle of. Lag, Angle of. ) 

opposite direction-during its motion past the south Current-Governor.— (See Governor, Cur- 

pole — from the bottom to the top. If, now, col- ren f\ 

lecting brushes rest on the commutator in the ClUTen t, "Homogeneous Distribution of 

positions shown in the Fig. 180. the vertical line ci.j-i.-Ui.- c ^l. i 

v & Such a distribution of a current through 

180° 

~d^?BHHHHI an y conductor in which there is an equal 

l^^llvi^v^H density of current at all portions of any 

, £^--~(2mIs- - ^-"hB cross-section of the conductor. 
f90 ? r ~ --fH - - - -27(« 

When the flow of a constant current is estab- 

-J>'—--Wk lished in a solid conducting wire, there is a 

~P- _~I^Hl homogeneous distribution of current in that con- 

0° a- 4. 

Fig. 180. Action of Commutator. aUCtOr. 

of the gap between the poles corresponding with Current, Induced The current 

the vertical gap between the commutator seg- produced in a conductor by cutting lines of 

ments, the currents generated in the loop will be force. 

caused to flow in one and the same direction, and The induced current results from differences of 

B', will become the positive brush, since the end potential produced by electro-dynamic induction. 

of the loop is connected with it only so long as it (See Induction, Electro- Dynamic.) 

is positive. As soon as it becomes negative, from Current - Induction. — (See Induction,. 

the current in the loop flowing in the opposite Curreiit ) 

direction, the other end, which is then positive, _, _ . 

. , lU i, ... u i. Current, Intensity of — An old 

is connected with the positive brush. . ' J 

A similar series of changes occur at the nega- term sometimes employed to indicate the 

tive brush B. current which resulted from a considerable 

Theoretically, the neutral points, where the difference of potential, or a great electromotive 

brushes rest, would be in the vertical line coincid- force. 

ing with that of the gap between the poles. An This term was also formerly used as synony- 

inspection of the figure shows that the neutral m ous with strength of current. 

line, or the diameter of commutation, is dis- This use of the term is now abandoned, 

placed in the direction of rotation. (See Commit- Voltaic batteries, connected in series so as to 

tation, Diameter of.) The displacement of the glve a considerable difference of potential, were 

brushes, so necessitated, is called the lead. spoken of as being connected for intensity. 

The cause of the lead is the reaction that occurs This term has also been used for the quantity 

between the magnetic poles of the field magnets f electricity conveyed per second across a unit 

area of cross -section. 

Intensity of current is more properly called 

/ '"^^t^B density of current. (See Current Density, ) 

' V r "> t b't)fr- ^hKH Current, Intermittent A current 

J fl/A '^' HUH t * iat c ^ oes not ^ ow contmua ^y» but which flows 

fa i'f/if JBSjt and ceases to flow at intervals, so that elec- 

^n rf TO r^™ tricky is practically alternately present and 

PQII^P^ absent from the circuit. 

Fig x8z Cause of Lead of Brushes. Current, Inverse-Secondary The 

i., M .., , ,, . x . .. , . make-induced current. (See Current, Make- 

and those of the armature, the result of which is v 

to displace the field magnet poles, and to cause a Induced) 

change in the density in the field. This is shown Current, Jacobi's Unit of Such 

in Fig, i8i, where the density of the lines offeree a current that when passed through a volta- 

mdicates the position of the diameter of commu- meter will liberate a cubic centimetre of 




Cur.J 



140 



[Cur. 



oxygen and hydrogen at O degrees C. and 
760 mm. barometric pressure. 

One Tacobi's unit of current equals 

10.32 
ampere. (Obsolete.) 

Current, Make-Induced —The 

current induced by a current in its own circuit 
on making or closing the same. 

The current produced in the secondary of 
an induction coil on the making or com- 
pletion of the circuit of the primary. 

The make-induced current is also called the 
inverse-secondary current, because its direction 
is opposite to that of the inducing current. 

Current, Make or Break Induced, Dura- 

tion of The time during which the 

induced inverse or direct-secondary currents 
continue. 

Blaserna made a number of experiments, which 
he claims shows : 

(1.) The greater the distance apart of the pri- 
mary and the secondary, that is, the less their 
mutual-induction, the less the maximum .value of 
the secondary current, and the greater the delay 
in establishing that maximum. 

(2.) The delay in establishing the maximum of 
the break or direct -secondary current is not as 
great as in the case of the make, or inverse-sec- 
ondary current. 

(3.) When the coils are near together, the in- 
duced currents at starting are established by a 
series of electric oscillations, 

(4.) The primary current establishes itself by a 
series of electrical oscillations. 

(5,) That the interposition of dielectric sub- 
stances, such as glass between 'he coils, 'educes 
the time between tht making or breaking of the 
primary current and the beginning of the sec- 
ondary current. This last conclusion was nega- 
tived by some experiments of Bernstein. 

Blaserna determined in the ca<=e of certain ex- 
periments the following value for the durations of 
the secondary currents : 

Inverse -secondary current lasts 000485 second. 

Direct -secondary current lasts .000275 second, 

Helmholtz contradicts the results of Blaserna, 
and asserts : 

(1.) That no perceptible difference in the zero 
points of the currents is produced by varying 
the distance between the primary and secondary. 

(2 ) That the sparks produced by the breaking 



of the primary last for an appreciable time, some- 
thing like T ^ ff to ^^ of a second. 

(3.) The duration of the break-spark is never 
constant, but depends in great part on the amount 
of platinum given off from the contacts at each 
spark. 

Current-Meter.— A form of galvanometer, 
(See Galvanometer,) 

Current, Momentary —A current 

that continues to flow but for a short time. 

Current, Multi-Phase A rotating 

current, (See Current, Rotating.) 

Current, Muscle In electro-thera- 
peutics, the current flowing through a muscle. 

Muscle currents are produced either by stimu- 
lation, or during activity of a muscle. According 
to L. Hermann, uninjured muscles, or perfectly 
dead muscles, yield no currents, but such cur- 
rents result only from an injury, (See Current, 
Demarcation , ) 

Current, Non Homogeneous Distribution 

of —Such a distribution of current pass- 
ing through a conductor in which there is an 
unequal density of current at all portions of 
any cross-section of the conductor. 

When a rapidly alternating current is passed 
through any solid conductor, the current density 
is greater at the surface and less towards the 
centre. The current distribution in such a con 
ductor is non homogeneous, and the want of uni • 
formity of current density is greater as the rapid- 
ity of alternation or periodicity is greater. 

Current, Outgoing —The current 

sent out over the line from a station provided 
with a duple < or quadruplex transmission, as 
distinguished from the received current. (See 
Current, Received.) 

Current, Periodic —A simple 

periodic current. (See Currents, Simple 
Periodic?) 

Current, Periodic, Power of An 

amount of work, per second, equal to the 
product of the electromotive force taken at 
successive moments of time during a com- 
plete cycle, multiplied by the current strength 
taken at the corresponding moments during 
the cycle, 

Since the electromotive force and current in 



Car.] 



141 



[Cur. 



a periodic circuit may be represented by two 
simple harmonic functions, the mean value of 
the two, when of different amplitude and phase, 
is equal to the product of their maximum value 
by the cosine of their difference of phase divided 
by two. 

Current, Polarization In electro- 
therapeutics, the constant current which when 
passed through a nerve produces in it the 
electrotonic state. (See Electrotomcs.) 

Current. Pulsating" A pulsatory 

current. (See Current, Pitlsatory.) 

Current, Pulsatory A current, the 

strength of which changes suddenly. 

The pulsatory current usually consists of sudden 
and distinct impulses, or rushes of current, in 
contradistinction to an undulatory or harmonically 
varying current. 

Current, Received The current 

received from the distant end of the line at a 
station provided with a duplex or quadruplex 
transmission as distinguished from the out- 
going current. 

A term sometimes used in telegraphy to 
distinguish between currents that come in over 
the line from a distant station, and those 
that are sent out to a distant station. 

Current. Rectilinear — A current 

flowing through straight or rectilinear por- 
tions of a circuit. 

In studying the effects of the attractions or repul- 
sions produced by electric currents the name ex- 
pressing the peculiarity of shape of any part of 
the circuit is often applied to the current flowing 
through that part of the circuit. Thus we speak 
of a rectilinear current, a sinuous current. 

Current, Reverse-Induced — The 

current induced by a current in its own cir- 
cuit at the moment of making or closing the 
circuit. 

The current induced in the secondary on 
closing or making the circuit of the primary. 

This is called the reverse-induced current, be- 
cause its direction is opposite to that of the current 
in the inducing circuit. 

Current, Reversed A current whose 

direction is changed at intervals. (See Cur- 
rent, Altertiating.) 



Current Reverser. — (See Reverser, Cur- 
rent.) 

Current, Reversing a Changing the 

direction of an electric current. 

Current, Rotating A term applied 

to the current which results by combin- 
ing a number of alternating currents, whose 
phases are displaced with respect to one an- 
other. 

A rotating current is sometimes called a poly- 
phase or ?nultiple-phase current, particularly if 
there are three or more currents combined. 

The rotating current is employed by Tesla, 
Dobrowolsky and others in a system of distribu- 
tion by transformers in place of the ordinary 
alternating current. In practice, three alternating 
current are combined. The currents and their 
combination are obtained by means of a specially 
constructed alternator. When three currents are 
combined the displa;ement between each set of 
phases is 1 20 degrees. A rotating current, unlike 
an alternating current, possesses, in a certain 
sense, a definite direction of flow. Its effect on a 
magnetic needle is to cause rotation. Hence 
motors constructed on the principle of rotating 
currents will start with a load. 

Current, R atatory • Phase • Alternating 

A term sometimes employed for a 

rotating electric current (See Current, Ro- 
tating.) 

Current, Secretion In electro- 
therapeutics, a current following stimulation 
of the secretory nerves. 

Current, Simple-Harmonic A term 

sometimes usrd instead of simple-periodic 
current. (See Currents, Simple Periodic?) 

Current, Sinuous A term some- 
times applied to currents flowing through a 
sinuous conductor. 

Sinuous currents exert the same effects of attrac- 
tion or repulsion on magnets, or on neighboring 
circuits, as would a rectilinear current whose 
length is that of the axis of such sinuous current. 

This can be shown by approaching the circuit 
A' B', Fig. 182, consisting of the sinuous con- 
ductor A', and rectilinear conductor B', to the 
movable conductor ABC, on which it produces 
no effect. The current A', therefore, neutral- 



Cur.] 



142 



[Cuiv 



izes the effects of the current B' ; or, it is equal to 
it in effect. 




Fig. 182. Rectilinear Equivalent of Sinuous Current. 

In calculating the effects of sinuous currents it 
is convenient to consider them as consisting of a 




Fig. 183. Sinuous Currents. 
succession of short, straight portions at right an- 
gles to one another, as shown in Fig. 183. 

Current, Steady A current whose 

strength does not vary from time to time. 

In a steady current the quantity of electricity 
flowing through each unit of area of the equi- 
potential surface of the conductor is the same for 
each succeeding interval of time. Such a current 
is sometimes called a uniformly distributed cur- 
rent. 

Current Streamlets. — (See Streamlets, 
Current?) 

Current Strength. — The product obtained 
by dividing the electromotive force by the 
resistance. 

The current strength for a constant current 
according to Ohm's law is — 



Current strength is proportional to the amount 
of the magnetic or chemical (electrolytic) effects 
it is capable of producing. 

For a simple-periodic current, the current 
strength necessarily varies from time to time. 

The average current strength of a simple- 
periodic current is equal to the average impressed 
electromotive force divided by the impedance. 
(See Impedance. ) 

The maximum current strength is equal to the 
maximum impressed electromotive force divided 
by the impedance. 

Current, to Transform a To 

change the electromotive force of a current 
by its passage through a converter or trans- 
former. 

To convert a current. 

Current, Transforming- a Chang- 
ing the electromotive force of a current by its 
passage through a converter or transformer. 

Current, Undulating An undu- 

latory current. (See Currents, Undulatory?). 

Current, Uniformly-Distributed - 



A term sometimes employed in the same 
sense as steady current. (See Current, 
Steady?) 

Current, Unit Strength of Such 

a strength of current that when passed 
through a circuit one centimetre in length, 
arranged in an arc one centimetre in radius,- 
will exert a force of one dyne on a unit mag- 
net pole placed at the centre. 

This absolute unit is equal to ten amperes or" 
practical units of current. (See At?ipere.) 

Current, Variable Period of 

The period which exists while an electric 
current is being increased or decreased in 
strength, or while it is being reversed. 

Currents, Action Physiological cur- 
rents obtained during the activity of a muscle 
or nerve. 

Currents, After In electro-thera- 
peutics, currents produced in nervous or' 
muscular tissue when a constant current, 
which has been flowing through the same, 
has been stopped. 

After currents are due to internal polarization. 

Currents, Alternating-Primary 

The currents employed in the primary of a 



Cur.] 



143 



[Cur. 



transformer to induce alternating currents in 
the secondary. (See Transformer?) 

Currents, Alternating-Secondary — 

The currents induced in the secondary of a 
transformer by the alternating currents in the 
primary. (See Transformer?) 

Currents, Alternating, Shifting of Phase 

of (See Phase, Shifting of, of Alter- 
nating Currents?) 

Currents, Amperian The electric 

currents that are assumed in the amperian 
theory of magnetism to flow around the mole- 
cules of a magnet. (See Magnetism, Ampere s 
Theory of.) 

The amperian currents are to be distinguished 
from the eddy, Foutault, or parasitical currents. 
since, unlike them, they are directed so as to pro 
duce useful effects. (See Currents, Eddy ) 

It is not believed that the amperian currents 
are produced in magnetizable substances by the 
act of magnetization. The atoms or molecules 
were magnetic originally. All the magnetizing 
force does is to arrange the molecules or atoms, 
or to set them in one and the same direction. 

Currents, Angular Currents flow- 
ing through circuits that cross or are inclined 
to one another at any angle. (See Dynaimcs, 
Electro) 

Currents. Atomic A term some- 
times used instead of molecular or amperian 
currents. (See Currents Amperian) 

Currents, Attractions and Repulsions 

of The mutual attractions or repul- 
sions exerted by currents on one another 
through the interaction of their magnetic 
fields. (See Dynamics, Electro?) 

Currents, Commuted Electric cur- 
rents that have been caused to flow in one 
and the same direction. (See Commutator?) 

Currents, Commuting — Causing 

several currents to flow in one and the same 
direction. 

Currents, Component The two or 

more currents into which it may be conceived 
that a single current can be divided, so as 
to produce the same effects of attraction or 
repulsion that the single current would do. 



The idea of component currents is based on the 
similar idea of the components of any single 
force. 

Currents, Continuity of — The 

freedom from variation in current strength or 
current direction. 

Currents, Convection — Currents 

produced by the bodily carrying forward of 
static charges in convection streams. (See 
Streams, Convectioii?) 

In a convection current, the static charge is 
bodily carried forward. 

Rowland has shown experimentally that a 
moving electric charge is the equivalent of an 
electric current. He rotated a gilded ebonite 
disc between two gilt glass discs, near which 
were placed a number of delicate magnetic 
needles. When certain rapidity of rotation was 
obtained, the discs were found to affect the mag- 
netic needles the same as would a current of elec- 
tricity flowing in a circular conductor, whose 
form coincided with the periphery of the disc. 

Currents, Converted Electric cur- 
rents changed either in their electromotive 
force or in their strength, by passage through 
a converter or transformer. (See Trans- 
for?ner?) 

Currents, Converting Changing 

the electromotive force of currents by their 
passage through a converter or transformer. 
(See Transformer?) 

Currents. Diaphragm Electric cur- 
rents produced by forcing a liquid through 
the capillary pores of a diaphragm. (See 
Osmose, Electric?) 

Currents, Earth Electric currents 

flowing through the earth, caused by a differ- 
ence of potential at different parts. 

The causes of these diffe-ences of potential are 
various and are not well understood. 

Currents, EHy ■ —Useless currents 

produced in the pole pieces, armatures, field- 
magnet cores of dynamo-electric machines or 
motors, or other metallic masses, either by 
their motion through magnetic fields, or by 
variations in the strength of electric currents 
flowing near them. 

Sensible eddy currents are producd in the mass 



Cur.l 



141 



lur. 



of the conducting wire on the armature of a 
dynamo-electric machine when the wire is com- 
paratively heavy. 

Such currents are called eddy currents, local 
currents, Foucault currents, or parasitical cur- 
i ents. They form closed -circuits of comparatively 
low resistance, and tend to cause undue heating of 
armatures or pole pieces. They not only cause a 




Fig. 184. Foucault Currents in Pole Pieces. 

useless expenditure of energy, but interfere with 
the proper operation of the device. 

To reduce them as far as practicable, the pole 
pieces, armature cores or armature wires, are 
laminated. (See Core, Lamination of.) 

These local currents are perhaps preferably 
called Foucault currents when they take place 
in magnetic cores, pole pieces or armature 
cores, and eddy currents when they occur in the 
armature wire or conductor. When the armature 
conductor is made up of copper bars, for exam- 
ple, the eddy currents in the latter are usually 
considerable 

Since Foucault currents in dynamo-electric ma- 
chine cores are due to variations in the magnetic 




Fig. 185. Foucault Currents in Pole Pieces. 

strength of the field magnets, or of the arma- 
ture, they will be of greatest intensity when the 
changes in the magnetic strength are the greatest 
and most sudden. 

These changes are most marked, and conse- 
quently the Foucault currents are strongest at those 
corners of the pole pieces of a dynamo from which 
the armature is moved in its rotation, as will be 
seen from an inspection of Fig. 184. 

Fig. 185, shows Foucault currents generated in 
pole pieces. 



Currents, Eddy-Conduction —A 

term employed for ordinary eddy currents in 
conductors, in order to distinguish them from 
eddy-disp'acement currents. (See Currents, 
Eddy-Displacement '.) 

Currents, Eddy Deep Seated Eddy 

currents set up in the mass of a conductor sub- 
jected to electro-dynamic induction in con- 
tradistinction to superficially seated eddy cur- 
rents. (See CurreJtts, Eddy, Superficial) 

Currents, Eddy-Displacement — 

Eddy currents produced in the mass of a 
dielectric or insulator, when lines of magnetic 
or electrostatic force pass through the di- 
electric or insulator. 

Eddy-displacement currents are produced in 
a dielectric or non-conductor, when it is moved 
across a magnetic field, so as to cut the lines of 
magnetic force. 

Eddy displacement currents would also occur 
if a dielectric is subjected to varying electrostatic 
induction. 



Currents, Eddy, Superficial 



-Eddy 



currents produced in conducting substances 
that are limited to the outer layers thereof. 

The eddy currents produced by alternating 
currents are superficial if the alternating currents 
are sufficiently rapid. The oscillatory currents pro- 
duced during the discharge of a Leyden jar are 
more superficial in proportion as the discharge 
takes place rapidly. When currents are pro- 
duced in a magnetizable body by the discharge 
of a Leyden jar, they are more and mo- e super- 
ficial, as the discharge of the jar is more and more 
rapid. The reason a slow discharge of a jar or 
condenser produces a greater magnetizing effect 
is, because of the checking or screening action 
the superficial eddy currents exert on the interior 
of the mass of the magnetizable substance when 
the discharge is very rapid. 

Currents, Electrotonic In electro- 
therapeutics, currents due to internal polariza- 
tion in the nerve fibre between the conduct- 
ing core of the nerves and the enclosing 
sheaths. 

Currents, Extra Currents pro- 
duced in a circuit by the induction of the 
current on itself on the ooeninor or closing of 



Cur.] 



145 



LCur. 



the circuit (See Cttrrents, Extra. Indite- 
Hon, Self.) 

The extra current induced on breaking, flows 
in the same direction'as the original current and 
acts to strengthen and prolong it. 

The extra current induced on making or com- 
pleting a circuit flows in the opposite direction 
to the original current and tends to oppose or re ■ 
tard the current. 

Both of these currents are called induced or 
extra currents. The former is called the direct- 
induced current, and the latter the reversed-in- 
duced current. (See Current, Direct-Induced. 
Current, Reversed- Induced. ,) 

In order to distinguish this induction from that 
produced in a neighboring conductor by the pas- 
sage of the electric current, it is called selj -induc- 
tion. (See Induction, Self. Induction, Mutual.) 

The effect on a telegraphic line of the self-in- 
duced or extra currents is to decrease the speed ot 
signaling by retarding the beginning of a signal, 
and prolonging its cessation, 

The greater the number of turns of wire in a 
circuit, or magnet, and the greater the mass ot 
iron in its core, the greater the strength ot the 
extra currents. 

Currents, Foucault — A name some- 
times applied to eddy currents, especially in 
armature cores. (See Currents, Eddy) 

Currents, Heating Effects of The 

heat produced by the passage of an electric 
current through any circuit. (See Heat, Elec- 
tric) 

Currents, Imbibition —Currents 

produced in tissues by the imbibition or ab- 
sorption of a fluid. 

Imbibition currents are a species of diaphragm 
currents. The absorption of a fluid at the 
demarcation surface of an injured nerve or 
muscle, or at the contracted portion of muscles, 
produces imbibition currents. 

Such currents are also produced in plants by 
the movement of fluids produced by bending the 
stalk or leaves, or by active movements of certain 
sensitive plants. 

Currents, Induced-3Iolecular or Atomic 

Currents induced in the atoms or 

molecules of a magnetizable substance on its 
being brought into a magnetic field. 

These currents are called induced -molecular, 
or induced -atomic currents in order to distin- 



guish them from the molecular, atomic or amperian 
currents, or the currents which are assumed to be 
always present. It is by the presence of these 
assumed induced-molecular currents that the 
pheno nena of diamagnetism are explained by 
Weber. (See Diamagnetism, Weber's Theory 
of.) 

Currents, Local A name sometimes 

applied to eddy currents. (See Currents, 
Eddy.) 

Currents, Molecular or Atomic — - — 

A term sometimes employed for amperian 
currents. (See Currents, Amperian.) 

Currents, Natural — A term some- 
times applied to earth currents. (See Cur-> 
rents Earth.) 



Currents, Negative 



-A term em- 



ployed in single-needle telegraphy for cur- 
rents sent over a line in a negative direction 
by depressing a key that connects the line 
with the negative pole of a battery and so 
deflects the needle to the left. (See Teleg- 
raphy, Single-Needle) 

Currents, Network of — A term 

sometimes applied to a number of shunt or 
derived circuits. (See Circuit, Shunt. Cir- 
cuit, Derived. Laws, Kirchhojf's.) 

Currents of Motion. — A term sometimes 
employed in electro-therapeutics for the cur- 
rents of electricity that traverse healthy 
muscle or nerve tissue during the sudden con- 
traction or relaxation thereof. 

The existence of these currents is denied by 
some, 

Currents of Rest.— A term sometimes em- 
ployed in electro-therapeutics for the cur- 
rents of electricity that traverse healthy 
muscle or nerve tissue while the muscles are 
passive. 

The existence of these currents is denied by 
some. 

Currents, Orders of —Induced elec- 
tric currents named from the order in which 
they are induced, as currents of the first, 
second, third, fourth, etc., orders. 

An induced current can be caused to induce an. 
other current in a neighboring circuit, and this a 
third current, and so on. Such currents are dis- 



Cur.] 



146 



[Cur. 



tinguished by the term, currents of the second, 
third, fourth, etc., order. (See Coils, Henry's.) 



Currents, Parasitical 



name 
(See 



sometimes applied to eddy currents 
Currents, Eddy?) 

Currents, Positive A term em- 
ployed in single-needle telegraphy for currents 
sent over the line in a positive direction by de- 
pressing a key that connects the line with 
the positive pole of a battery and so deflects 
the needle to the right. (See Telegraphy, 
Single-Needle .) 

Currents, Reversed A name some- 
times applied to alternating currents. (See 
Current, Alternating?) 

Currents, Secondary The currents 

produced by secondary batteries in contra- 
distinction to the currents produced by 
primary batteries. 

The currents produced by the secondary 
conductor of an induction coil, as distinguished 
from the currents sent into the primaries, 

This second use of the term secondary current 
is more usual. 

Currents, Self-Induced A current 

produced by self-induction. 

An extra current. (See Induction, Self. 
Currents, Extra?) 

Currents, Simple Periodic —Cur- 
rents, the flow of which is variable, both in 
strength and duration, and in which the flow 
of electricity, passing any section of the con- 
ductor, may be represented by a simple peri- 
odic curve. 

A current of such a nature that the con- 
tinuous variation of the flow of electricity 
past any area of cross-section of the con- 
ductor, or the variations in the electromotive 
force of which can be expressed by a simple- 
periodic or harmonic curve. (See Curve, 
Simple-Harmonic?) 

Alternate currents are simple-periodic currents. 

The average current strength of simple-periodic 
currents is equal to the average impressed electro- 
motive force divided by the impedance. 

The transmission of rapidly varying or sim- 
ple-periodic currents through conductors differs 
ve-y greatly from the transmission of steady cur- 



rents. With a steady current, the current density 
is the same for all areas of cross-section of the 
conductor. For a rapidly intermittent current, 
the current density is greater near the surface, 
and when the rate of intermission is sufficiently 
great, the current is entirely absent at the centre 
of the conductor. 

Lord Rayleigh has shown that when the rate of 
intermission is 1,050 per second, the effective re- 
sistance of a wire 160 mm. in length, and 30 mm. 
in diameter, is 1 .84 times its resistance to steady 
currents. He found that the increase of resist- 
ance is greater in the case of conductors of great 
diameter than in those of small diameter, 

As regards the character of conductor best 
suited for transmitting rapidly alternating cur- 
rents, it can be shown : 

(1.) That for transmitting alternate currents of 
moderate frequency, say of about i,ooo per sec- 
ond, copper conductors should be used in prefer- 
ence to rods of iron. 

(2.) That the conductor should be in the form 
of thin strips, or if tubular, of thin walls. 

(3.) That the mere stranding of the conductor, 
i. e., forming it of separate insulated conductors 
connected in parallel, will be of no effect in pre- 
venting the current from acting on the outside of 
the conductor, unless the conductor be arranged 
in the form of a cable, in which one part forms a 
lead, and another part the return. 

Stephan draws the following analogy between 
the flow of alternating currents in a conductor 
and the flow of heat in a hot wire : 

' ' Suppose a wire or conductor, uniformly heated 
from centre to circumference, be suddenly taken 
into a space where the temperature is high, the 
outer portions of the wire first rise in temperature, 
and afterwards the inner portions. In the case of 
a conductor of circular cross-section, the heat 
penetrates successive concentric layers. The same 
phenomena occur when an electromotive force is 
suddenly set up between the ends of a cylindrical 
conductor. The current gradually penetrates the 
conductor from the outside to the centre. 

' ' Now suppose the heated wire is carried into a 
cooler space, the heat waves pass out radially 
from the centre towards the circumference. The 
cooling wire corresponds to the case of a con- 
ductor in which the external electromotive force 
is suddenly removed." 

According to this conception, the heat conduct- 
ing power of any substance corresponds to its 
electrical conducting power. 



Cur. 



147 



[Cur. 



According to Stephan, in the case of a con- 
ductor of iron of 4 mm. in diameter, traversed by 
an alternating current of 250 alternations per 
second, the current density on the surface is about 
twenty-five times as great as that at its axis. 

Where the conductor is of non- magnetic mate- 
rial, the difference in the current density is not bo 
marked. 

Rapidly intermittent currents produce a real 
increase in the resistance of the conductor, which 
must not be confused with the fact that the impe- 
dance is greater than the ohmic resistance, but 
rather as an actual increase in the rate at which 
energy is dissipated per unit of current. 

Since current density is greatest at the outside 
portions of a conductor, and the central portions 
are nearly, if not entirely, deserted by the cur- 
rent, we may regard the conductor as having 
the ohmic resistance of a hollow cylinder of the 
same diameter as the conductor, with a cor- 
respondingly smaller area of cross-section, and 
therefore, of greater ohmic resistance per unk of 
length. 

The condition of affairs in the case of a con- 
ductor in which a current of electricity is begin- 
ning to flow, is now very generally regarded 
somewhat as follows, viz.: 

The current begins at the surface of the con- 
ductor, and more or less slowly soaks through 
towards the centre. If the current is constant, the 
current soon reaches the deepest layers; but, if it 
is rapidly intermittent, before it can soak very far 
into the conductor towards its axis, it is turned 
back towards the surface, and so becomes con- 
fined to layers which will be more and more super- 
ficial, as the rapidity of reversal increases. 

Therefore, for convenience, we may regard a 
solid conductor, through which a rapidly inter 
mittent current of electricity is flowing, as being 
practically converted into a hollow cylinder of 
the same diameter as the solid conductor, the 
area of cross-section of which hollow cylinder 
becomes smaller and smaller, as the rapidity of 
alternation is increased. 

Another, and perhaps the more correct concep 
tion of the condition of affairs in a solid conductor 
traversed by a rapidly alternating current of elec- 
tricity, has been pointed out by Maxwell, and after- 
wards by Heavyside, Rayleigh and Hughes. This 
conception is to regard the central portions of the 
conductor as possessing a counter electromotive 
force greater than the outer portions. The entire 
current flowing across any section of a conductor 



may be regarded as made up of little current 
streamlets, parallel to one another. 

The central streamlets, or filaments, from their 
mutual induction on one another, experience a 
greater resistance in 'reaching their full strength 
than the surface filaments do. Taken in this 
sense, we may state generally that the transmis- 
sion of rapidly alternating currents through con- 
ductors depends on the inductance, rather than 
on the resistance; but for steady currents, it de- 
pends more on the resistance than on the induct- 
ance. 

In periodic or oscillatory currents, as those 
produced by the discharge of a Ley den jar, or 
condenser, the surface streamlets have a current 
density far greater than the central streamlets. 

The true or ohmic resistance of the circuit is a 
minimum when the current is uniformly distrib- 
uted through all parts of the cross- section of the 
conductor, and the dissipation of energy through 
the generation of heat is less than for any other 
distribution. 

The conception of a periodic current flowing 
through a conductor, starting from the surface 
and gradually soaking in towards the centre, 
regards the energy of an electric current — not as 
being pushed through the conductor, as water 
through a pipe, but as actually being absorbed at 
its surface, from the surrounding dit-lectric, or as 
being, so to speak, rained down on the conductor 
from the space outside of it. 

Currents, Swelling" In electro- 
therapeutics, currents that begin weak and are 
gradually made stronger and then weaker. 

Currents, STvelling-Faradic —A 

term employed in electro-therapeutics for fara- 
die currents that are caused to gradually in- 
crease in strength and then to gradually de- 
crease to zero strength. 

Currents, Transient Currents that 

are but of momentary duration. 

Currents, Undulatory Currents the 

strength and direction of whose flow gradually 
change. 

The term undulatory currents is used in con- 
tradistinction to pulsatory currents, in which the 
strength changes suddenly. In actual practice, 
such currents differ from undulatory currents 
more in degree than in kind, since, when sent 
into a line, the effects of retardation tend to 
obliterate, to a greater or less extent, the sudden 



Cur.] 



148 



[Cur. 



differences in intensity on which their pulsatory 
character depends. 

The currents produced in the coils of the Sie- 
mens magneto- electric key, in which the me- 
chanical to-and-fro motion of the key sends elec- 
trical impulses into the line, are, in point of fact, 
undulatory in character, when they follow one an- 
other rapidly. 

The currents in most dynamo-electric machines, 
the number of whose armature coils is compara- 
tively great, are, so far as the variations in their 
intensity or strength are concerned, undulatory 
in character even when non-commuted. 

The currents on all telephone lines that trans- 
mit articulate speech are undulatory. This is 
true, whether the transmitter employed merely 
varies the resistance by variations of pressure, or 
actually employs makes-and-breaks that rapidly 
follow one another. — (See Current, Pulsatory. 
Current, Intermittent.) 

Curtain, Auroral — A sheet of 

auroral light having the shape of a curtain. 
(See Aurora Borealzs.) 



The ballistic curve has a smaller vertical height 
than the parabola. The projectile also has a- 



Curve, Asymptote of 



-A straight 




line which continually approaches a curved 
line, but meets or becomes tangent to such 
curved line only at an infinite distance. 

In Fig. 1 86, the curve C D, continually ap- 
proach tli,' asymptote y z, but never meets it. 

It is at first difficult to un- 
derstand how one line can 
continually approach an- 
other and yet never meet it. 
But it will be readily under- 
stood if it is remembered & 
that in all cases of asymp- Fi S- i 8 *>- Asymptote 
totic approach each advance °f Curve - 

becomes smaller and smaller. 

This mathematical conception is like a value 
which, although constantly reduced to one-half 
of its former value, is nevertheless never reduced 
to zero or no value. 

Curve, Ballistic The curve ac- 
tually described by a projectile thrown in 
any other than a vertical direction through 
the air. 

The path of a projectile in a vacuum is a para- 
bola—that is, the path A E B, Fig. 187. In air, 
the effects of fluid resistances cause the projectile 
to take the path A C D, called a ballistic curve. 




>1 F 
Fig. 187. Ballistic Curve. 

smaller vertical range. Instead of reaching the 
point B, it continually approaches the perpen- 
dicular E F. 



Curve, Characteristic 



-A diagram: 



in which a curve is employed to represent 
the ratio of certain varying values. 

The electromotive force generated in the arma- 
ture coils of a dynamo-electric machine, when the 
magnetic field is of a constant intensity, is theo- 
retically proportional to the speed of rotation. In 
practice this is modified by a number of circum- 
stances. 

The relation existing between the speed 
and electromotive force may be graphically rep - 
resented by referring the values to two straight 
lines, one horizontal and the other vertical, called 
respectively the axes of abscissas and ordinates. 
(See Abscissas, Axis of.) If, in a given case, the- 
number of revolutions 
is marked off along 
the horizontal line 
from the point o, Fig. 
188, in distances from 
o, proportional to the 
number of revolu- 
tions, and the corre- 
sponding electromo- 
tive forces are marked 
off along the vertical line in distances from o, 
proportional to the electromotive forces, the 
points where the=e lines intersect will form the 
characteristic curve as shown in Fig. 188. 

Curve, Characteristic, of Parallel Trans- 
former — A curve so drawn that its 

ordinate and abscissa at any point represent 
the secondary electromotive force and the sec- 
ondary current of a multiple connected trans- 
former, when the resistance of the secondary 
circuit has a certain definite value. 

With a constant electromotive force in the pri- 




Fie 



J 500 100 

Revolutions. 

188. Characteristic 
Curve. 



Car.] 



149 



[Cuiv 



mary circuit, i. e., with the transformers in parallel, 
the characteristic curve is a straight line parallel 
to the axis of the current. This curve, as shown 
in Fig. 189, is practically a straight line. The par- 
allel transformer will be 
practically self regulating 
under a constant primary 
electromotive force. 

According to Forbes, if ' a X 

a transformer has its lamp Fig% jgg. Character- 
load in parallel with the istic of Parallel Trans- 
secondary circuit, the ex- former. 
tinction of its lamps will decrease the efficiency 
of the transformer. The efficiency is therefore 
less for light loads than for heavy loads of parallel 
lamps up to a certain point. 

Curve, Characteristic, of Series Trans- 
former A curve so drawn that its 

ordinate and abscissa at any point represent 
the secondary electromotive force and second- 
ary current of a series-connected transformer, 
when the resistance of the secondary current 
has a certain definite value. 

Fig. 190 shows characteristic curve of a series 




Fig. iqo. Characteristic of Series Transformer. 

transformer. O a, is drawn perpendicular to the 
line representing the secondary current, and a b, 
perpendicular to O a, represents the correspond- 
ing secondary electromotive force. The various 
positions of b, as different values are given to O a, 
produce the elliptic curve which is the character- 
istic curve of the series cransformer. 

"A series transformer," says Fleming, "with 
a core sufficiently large to avoid saturation, can 
never be self- regulating if so used. It can only 
be made self-regulating with a non- saturated core, 
when working near the extremities of its charac- 
teristic, either with a small secondary current 
or a low electromotive force. Both of these con- 
ditions are uncommercial." 

Curve, Life, of Incandescent Lamp 



— A curve in which the life of an electric 
lamp is represented by means of abscissas and 
ordinates proportional to the life in hours and 
the candle-power or the volts respectively. 

Curve, Logarithmic A curve in 

which the rate of increase or decrease of the 
ordinate is proportional to the ordinate itself. 

On the line O X, Fig. 191, mark off the time 

Y— _-,_ 9 




rithmic Curve, 



in lengths, reckoned from O. Represent the 
current strength by lines drawn vertically to the 

E 

time-line. Let O Y, equal C = ^p 

Applying the electromotive force, the current 
grows in the wire as represented by the graphic 
curve. 

According to Fleming, the growth of this cur- 
rent takes place according to the following law, 
viz.: "The current strength at any instant, 
added to the rate of growth of the current strength 
at that instant multiplied by the time-constant, is 
equal to the current which would exist if indu:- 
tion were zero. ' ' 



Curre, Permeability 



— A curve repre- 
senting the magnetic permeability of a mag- 
netic substance. 

There is a certain temperature for every para- 
magnetic substance, at which its permeability is 
no greater than that of air. This temperature 
for iron is reached at about 750 degrees C; for 
nickel, at about 400 degrees C. 

Curve, Simple-Harmonic —The 

curve which results when a simple-harmonic 
motion in one line is compounded with a uni- 
form motion in a straight line, at right angles 
thereto. 

A harmonic curve is sometimes called a curve 
of sines, because the abscissas of the curve are 
proportional to the times, while the ordinates are 
proportional to the sines of the angles, which are 
themselves proportional to the times. 



Cur.] 



150 



[Cut. 



Curves, Isochasiuen Curves drawn 

on the earth's surface between zones having 
equal frequency of auroral discharges. 

The isochasmen curves are nearly at right 
angles to the magnetic meridian. 

Curves, Magnetic — Curved lines 

showing the direction of the lines of mag- 
netic force in any field, formed by sprinkling 
iron filings on a sheet of paper or glass held 
in the field of a magnet, and gently tapping 
the support so as to permit the filings- to prop- 
erly arrange themselves. (See Figures, 
Magnetic?) 

Cut-In, To To introduce an electro- 
receptive device into the circuit of an electric 
source by completing or making the circuit 
through it. 

Cut-Off, Automatic Gas A device 

for automatically cutting out the battery 
from an electric gas-lighting circuit on the 
accidental grounding of the circuit. 

Unless the battery is disconnected from the cir- 
cuit on the establishing of a ground, the battery 
will polarize and soon become useless. 

Cut-Out, A A device by means of 

which an electro-receptive device or loop may 
be thrown out of the circuit of an electric 
source. 

In any system of light or power distribution, a 
cut out is generally placed outside a building 
into which a loop or branch of the main circuit 
runs, so as to permit that loop or branch to be 
readily disconnected therefrom. In the same way 
cut-out keys or switches are generally placed in 
the circuit of the loop and each electro-receptive 
device. 

Cut-Out, Air-Space — A modified 

form of paper cut-out, in which the disc of 
paper or mica is replaced by the resistance of 
an air-space. 

Although the resistance of an air-space is so 
high as to be practically immeasurable, yet it is 
overcome or broken by a much lower differ- 
ence of potential than an equal thickness of 
paper or mica. (See Path, Alternative. Cut- 
Out, Film.) 



Cut-Out, Automatic Any device 

that will automatically cut-out, or remove, a 
translating device, or an electric source, from 
an electric circuit, whenever any predeter- 
mined effect is produced. 

Cut-Out, Automatic, for Multiple-Con- 
nected Electro-Receptive Devices 

A device for automatically cutting an electro- 
receptive device, such as a lamp, out of the 
circuit of the leads. 

Automatic cut-outs for incandescent lamps, 
when connected to the leads in multiple-arc, con- 
sist of strips of readily melted metal called safety 
fuses, which on the passage of an excessive cur- 
rent fuse, and thus automatically break the cir- 




Fig. IQ2, Ceiling Cut-Out. 

cuit in that particular branch. (See Catch, 
Safety.) 

A form of ceiling cut-out, made of porcelain, is 
shown in Fig. 192, with the two halves separated 




Ceiling Cut- Out, 



to show interior details, and in Fig. 193, with the 
two halves placed together. 



Cut.] 



151 



[Cyc 



Cut-Out, Automatic, for Series-Connected 

Electro-Receptive Devices A device 

whereby an electro-receptive device, such 
as an electric arc lamp, is, to all intents and 
purposes, automatically cut out, or removed 
from the circuit, by means of a shunt of low 
resistance, which permits the greater part of 
the current to flow past the lamp. 

It will be observed that the lamp, though still in 
the circuit, is to all practical intents cut out from 
the same, since the proportion of the current 
that now passes through it is too small to oper- 
ate it. 

In most series arc lamps, cut-outs are oper- 
ated by means of an electro -magnet placed in a 
shunt circuit of high resistance around the car- 
bons. If the carbons fail to properly feed, the 
arc increases in length and consequently in resist- 
ance. More current passes through the shunt 
magnet, until finally, when a certain predeter- 
mined limit is reached, the armature of the elec- 
tro-magnet is attracted to the magnet pole and 
mechanically completes the short circuit past the 
lamp. 

In some automatic cut-outs the fusion of a 
readily fused wire, placed in a shunt circuit 
around the carbons, permits a spring to complete 
the short circuit. 

The automatic cut-out prevents the accidental 
extinguishing of any single lamp in a series cir- 
cuit from extinguishing the remaining lamps on 
that circuit. 

Cut-Out, Automatic Time — A 

device arranged so as to automatically cut out 
a translating device, or an electric source, from 
a circuit, at the end of a certain predetermined 
time. 

Cut-Out, Duplex A cut-out so 

arranged that when one bar or strip is fused 
or melted by an abnormal current another can 
be immediately substituted for it. 

Cut-Out, Film A cut-out in which 

a film, or sheet of paper or mica, is interposed 
between a line plate and an earth plate, which, 
when punctured by a spark, short circuits the 
instruments on the line. 

Cut-Out, Main-Line — An auto- 
matic cut-out placed on the main line. (See 
Cut-Out, Automatic?) 



A form of main-line cut-QUt is shown in Fig. 




Fig. iQ4. Main-Line Cut-Out. 

194. The fuses are shown as attached to the fuse- 
block. 

Cut-Out, Paper A term sometimes 

employed instead of film cut-out. (See Cut- 
Out, FiZm.~) 

Cut-Out, Rosette — — —A rosette for an 
electrolier, containing a cut-out. (See Ro- 
sette?) 

Cut-Out, Spring-Jack A device 

similar in general construction to a spring- 
jack, but employed to cut out a circuit 

An insulated plug is thrust between spring 
contacts, thus breaking the circuit by forcing 
them apart. 

Cut Out, To To remove an elec- 
tro-receptive device from the circuit of an 
electric source by disconnecting or diverting 
the circuit from it. 

Cutting 1 Lines of Force. — (See Force, 
Lines of. Cutting) 

Cycle. — A period of time within which a 
certain series of phenomena regularly recur, 
in the same order. 

Cycle, Magnetic — - — A single round 
of magnetic changes to which a magnetizable 



Cyc] 



152 



[Dam. 



substance, such as a piece of iron, is subjected 
when it is magnetized from zero to a cer- 
tain maximum magnetization, then decreased 
to zero, reversed and carried to a negative 
maximum, and then decreased again to zero. 

Cyclical Magnetic Yariation. — (See Va- 
riation, Cyclical Magnetic?) 

Cyclotrope. — A name proposed in place 
of transformer or converter. (See Trans- 
former?) 

Cylinder, Yortex A number of 

vortex stream-lines grouped parallel to one 
another about a straight line which forms the 
axis or core of the vortex. 

Cylindrical Armature. — (See Armature, 
Cylindrical?) 

Cylindrical Carbon Electrodes. — (See 
Electrodes, Cylindrical Carbon?) 

Cylindrical Electro-Magnet. — (See Mag- 
net, Electro, Cylindrical?) 



Cylindrical Magnet. — (See Magnet, Cyl- 
indrical?) 

Cylindrical Ring Armature. — (See Arm- 
ature, Cylindrical Ring?) 

Cymogene. — An extremely volatile liquid 
which is given off from crude coal oil during 
the early parts of its distillation. 

The two liquids which are obtained from the 
condensation of the vapors given off during the 
first parts of the distillation of coal oil are called 
cymogene, and rhigolene. These liquids are em- 
ployed on account of their extreme volatility for 
the artificial production of cold. 

Rhigolene is employed by some for the treat- 
ment or flashing of the carbons used in incan- 
descent lamps. (See Carbons, Flashing Process 
for.) 

Cystoscopy, Electric A name given 

to Hitze's method of ocular examination 
of the human bladder by electric illumina- 
tion. 



Damped Magnetic Needle. — (See Needle, 
Magnetic, Damped?) 

Damper. — A metallic cylinder provided in 
an induction coil so as to partially or com- 
pletely surround the iron core, for the purpose 
of varying the intensity of the currents induced 
in the secondary. 

The metallic cylinder acts as a screen or shield 
for the rapidly alternating currents traversing the 
field of the primary. (See Screening, Magnetic.) 
As the damper is pulled out, a greater length of 
the core is exposed to the induction. 

Damper. — A term sometimes applied to a 
dash-pot or other similar apparatus provided 
for the purpose of preventing the too sudden 
movement of a lever or other part of a device. 
(See Dask-Pot) 

Some form of damper or dash-pot is used on 
most electric arc lamps, the upper carbon, of 
which is fed by a direct fall. 

The double use of this word is unfortunate. 

Damping. — The act of stopping vibratory 
motion such as bringing a swinging mag- 



netic needle quickly to rest, so as to deter- 
mine the amount of its deflection, without 
waiting until it comes to rest after repeated 
swingings to and fro. 

Damping devices are such as offer resistance 
to quick motion, or high velocities. T hose gen- 
erally employed in electrical apparatus are either 
air or fluid friction, obtained by placing vanes 
on the axis of rotation, or by checking the move- 
ments of the needle by means of the currents it 
sets up, during its motion, in the mass of any con- 
ducting metal placed near it. These currents, as 
Lenz has shown, always tend to produce motion 
in a direction opposed to that of the motion caus- 
ing them. Pell-shaped magnets are especially- 
suitable for this kind of damping. (See Magnet^ 
Bell Shaded.) 

The needle of a galvanometer is dead-beat when 
its moment of inertia is so small that its oscillations 
in an intense field are very quick, and the mirrcr, 
acting as a vane, causes the movements to die out 
very rapidly, and the needle therefore moves 
sharply over the scale from point to point and 
comes quickly to a dead, stop. When the needle 
or swinging coil is heavy and moves in an intense 



Dam, 



153 



[Dea. 



field, as in the Deprez-d'Arsonval galvanometer, 
the movements are dead-beat. 

Damping by means of pieces of india rubber is 
often applied to telephone diaphragms to prevent 
their excessive or continued vibration. 

Damping-, Electric — 



•(See Galva~ 



— A term some- 
times employed to express a decrease in 
the intensity of the electric oscillations pro- 
duced in a conductor by electric resonance, 
under circumstances where higher overtones 
are set up in the conductor. 

Daniell's Voltaic Cell.— (See Cell, Vol- 
taic, Daniell's.) 

Dark-Space, Crookes' (See Space, 

Dark, Crookes' .) 

Dark-Space, Faraday's (See Space, 

Dark, Faraday's.) 

Dash-Pot. — A mechanical device to prevent 
too sudden motion in a movable part of any 
apparatus. 

The dash-pot of an automatic regulator, or of 
an arc -lamp, is provided to prevent too sudden 
movements of the collecting brushes on the com- 
mutator cylinder, or the too sudden fall of the 
upper carbon. Such devices consist essentially of 
a loose fitting piston that moves through air or 
glycerine. 

Dash-pots are species of damping devices, and, 
like the damping arrangements on galvanometers 
or magnet needles, prevent a too free movement 
of the parts with which they are connected. (See 
Damper. Damping.) 

Day, Normal Magnetic A day dur- 
ing which the value of the earth's magnetic 
elements does not vary greatly from their 
mean value. (See Elements, Magnetic, of a 
Place.) 

Day of Disturbance, Magnetic — 

A day during which the mean departure of 
the readings of a declinometer at any place, 
from the normal monthly value at that place, 
is once and a half the average. — [Lloyd) 

Dead-Beat. — Such a motion of a galvanom- 
eter needle in which the needle moves sharply 
over the scale from point to point and comes 
quickly to rest. (See Damping.) 

Dead-Beat Discharge.— (See Discharge, 
Dead-Beat) 



Dead-Beat Galvanometer.- 

no7neter, Dead-Beat.) 

Dead Dipping. — (See Dipping, Dead.) 
Dead Earth. — (See Earth, Dead or Total.) 

Dead Turns of Armature Wire, or Dead 
Wire. — (See Turns, Dead, of Armature 
Wire) 

Death, Electric — Death resulting 

from the passage of an electric current 
through the human body. 

The exact manner in which an electric current 
causes death is not known. When the current is 
sufficiently powerful, as in a lightning flash, or a 
powerful dynamo current, insensibility is prac- 
tically instantaneous. 

Death may be occasioned: 

(i.) As the direct result of physiological shock. 

(2.) From the action of the current on the res- 
piratory centres. 

(3.) From the actual inability of the nerves or 
muscles, or both, to perform their functions. 

(4.) From an actual electrolytic decomposition 
of the blood or tissues of the body. 

(5.) From the polarization of those parts of the 
body through which the current passes. 

(6.) From an actual rupture of parts by a dis- 
ruptive discharge. 

TI12 current required to cause death will de- 
pend on a variety of circumstances, among 
which are: 

(1.) The particular path the current takes 
through the body, with reference to the vital 
organs that may lie in this path. 

(2.) The freedom or absence of sudden varia- 
tions of electromotive force. 

(3. ) The time the current continues to pass 
through the body. 

In some fatal cases, it is probably the extra- 
current, or the induced-direct current on break- 
ing, that causes death, since, as is well known, 
its electromotive force may be many times 
greater than that ot the original current. 

A comparatively low-potential continuous-cur- 
rent, cannot, therefore, be properly regarded 
as entirely harmless, simply because its electro- 
motive force is necessarily small. In the case of 
alternating currents the danger increases after a 
certain point with the number of alternations per 
second. When, however, the number of alter- 
nations per second reaches a given number, the 
danger decreases as the frequency of alternations 



Dec] 



154 



LDeg. 



increases. This was conclusively shown by the 
independent investigations of Tatum and Tesla. 

Decalescence. — A term proposed by Prof. 
Elihu Thomson for an absorption of sensible 
heat, which occurs at a certain time during 
the heating of a bar of steel. 

Decalescence will thus be observed to be the 
reverse of recalescence, which is the phenome- 
non of the emission of sensible heat at a certain 
time during the cooling of a heated bar of 
steel. (See Recalescence.) 

Deci (as a prefix). — The one-tenth. 

Deci-Ampere. — One-tenth of an ampere. 

Deci-Ampere Balance. — (See Balance, 
Deci- A mpere) 

Deci-Lux. — The one-tenth of a lux. (See 
Lux.) 

Declination. — The variation of a mag- 
netic needle from the true geographical north. 

The magnetic declination is east or west. (See 
Needle, Magnetic, Declination of.) 

Declination, Angle of The angle 

which measures the deviation of the mag- 
netic needle to the east 
or west of the true geo- 
graphical north. 

The angle of variation 
of a magnetic needle. 

In Fig. 195, ifNS, rep- 
resents the true north and 
south line, the angle of de- 
clination is N O A, and 
the sign of the variation is 
east, because the deviation of the needle is to- 
ward the east. (See Needle, Magnetic, Declina- 
tion of.) 

Declinometer. — A magnetic needle suit- 
ably arranged for the measurement of the 
value of the magnetic declination or varia- 
tion at any place. 

Decomposition. — In chemistry the separa- 
tion of a molecule into its constituent atoms 
or groups of atoms. (See Molecule. Alom.) 

Decomposition, Electric — Chem- 
ical decomposition by means of an electric dis- 
charge or current. 

This decomposition may result from an increase 




Fig 195. Declination 
of Needle. 



of temperature produced by the electric discharge, 
or from the passage of the current. In the latter 
case it is more properly called electrolytic decom- 
position. 

Decomposition, Electric, Crystallization 
"by (See Crystallization by Electro- 
lytic al Decomposition.) 

Decomposition, Electrolytic — 



- —The 

separation of a molecule into its constituent 
atoms or groups of atoms by the action of 
the electric current. 

These atoms or groups of atoms are either 
electro-positive or electro-negative in character. 
(See Electrolysis. Anion. Kathion.) 

De-energize. — To deprive an electro-recep- 
tive device of its operating current. 

De-energizing. — Depriving an electro- 
receptive device of its operating current. 

Deep-Seated Eddy Currents. — (See Cur- 
rents, Eddy, Deep-Seated) 

Deep-Water Submarine Cable. — (See 
Cable, Submarine, Deep-Sea) 

Deflagration, Electrical The fusion 

and volatilization of metallic substances by the 
electric current. 

Deflagrator. — The name given to a voltaic 
battery, of small internal resistance, employed 
by Hare in the electric deflagration of metal- 
lic substances. 

Deflection Method.— (See Method, Deflec- 
tion) 

Deflection of Magnetic Needle. — (See 
Needle, Magnetic, Deflection of) 

Degeneration. — Such a degeneration of the 
muscular or cellular structure of any cell or 
organ that incapacitates it from performing its 
functions. 

Degeneration of Energy. — (See Energy, 
Degeneration of) 

Degeneration, Partial, Reaction of 

— That form of alteration to electric stimula- 
tion, in which the nerves show no abnormal 
reaction to electric stimulation, while the 
muscles, when directly stimulated by the con- 
stant current, exhibit the reaction of degen- 
eration. (See DegeneratioJi, Reaction of)> 



Deg.] 



155 



[Dep. 



Degeneration, Reaction of — A 

qualitative and quantitative alteration of 
nerves and muscles to electric stimulation. 

According to Landois and Stirling the following 
conditions characterize essentially the reaction of 
degeneration: "The excitability of the muscles 
is diminished or abolished for the faradic cur- 
rent, while it is increased for the galvanic current 
from the third to the fifty-eighth day ; it again 
diminishes, however, with variations, from the 
. seventy -second to eightieth day ; the anodic clos- 
ing contraction is stronger than the kathodic 
closing contraction." * * * "The diminu- 
tion of the excitability of the nerves is similar for 
the galvanic and faradic currents." 

Deka (as a prefix). — Ten times. 

Deka-Ainpere. — Ten amperes. 

Deka-Ampere Balance. — (See Balance, 
Deka-Ampere) 

De la Rue's Standard Voltaic Cell. — (See 
Cell, Voltaic, Standard, De la Rue's.) 

Deliquescence. — The solution of a crystal- 
line solid arising - from its absorption of vapor 
of water from the atmosphere. 

Deinagnetizable. — Capable of being de- 
prived of magnetism. 

Demagnetization. — A process, generally di- 
rectly opposite to that for producing a magnet, 
by means of which the magnet may be de- 
prived of its magnetism. 

A magnet may be deprived of its magnetism, 
or be demagnetized — 

(i.) By heating it to redness. 

(2. ) By touching to its poles magnet poles of the 
same name as its own. 

(3.) By reversing the directions of the motions 
by which its magnetism was originally imparted, 
if magnetized by touch, by stroking it with a 
magnet in the opposite direction from that which 
would have to be given in order to produce the 
magnetization which is to be removed from it. 

(4.) By exposing it in a helix to the influence of 
currents which will impart magnetism opposite to 
that which it originally possessed. 

Avria claims that a smaller magnetizing force is 
required to demagnetize a needle than is required 
to magnetize it. 

Demagnetization of Watches.— (See 

Watches, Demagnetization of.) 



Demagnetize. — To deprive of magnetism. 

Demagnetizing. — Depriving of magnetiza- 
tion. 

Demarcation Current. — (See Current, De- 
marcation^) 

Demarcation Surface.— (See Surface,De- 

marcation.) 

Density, Electric The quantity of 

free electricity on any unit of area of surface. 

The density is said to be positive or negative 
according as to whether the charge is positive or 
negative. (See Charge, Density of. Plane, 
Magnetic Proof.) 

Density, Magnetic The strength 

of magnetism as measured by the number of 
lines of magnetic force that pass through a 
unit area of cross-section of the magnet, /. e., 
a section taken at right angles to the lines of 
force. (See Field, Magnetic.) 

Density of Charge. — (See Charge, Den- 
sity of) 

Density of Current. — (See Current 
Density) 
Density of Field.— (See Field, Density of) 

Density, Surface A phrase used 

by Coulomb to mean the quantity of elec- 
tricity per unit of area at any point on a sur- 
face. (See Charge Density. Density, 
Electric) 

Dental-Mallet, Electro-Magnetic — 

A mallet for filling teeth, the blows of which 
are struck by means of electrically-driven 
mechanism. 

Electro-magnetism was first employed for this 
purpose by Bonwill, of Philadelphia. 

Dentiphone. — An audiphone. (See Audi- 
phone) 

Depolarization. — The act of reducing or 
removing the polarization of a voltaic cell 
or battery. (See Cell, Voltaic, Polarization 
of) 

Depolarize. — To deprive of polarization. 

Depolarizing. — Depriving of polarization. 

Depolarizing Fluid. — (See Fluid, De- 
polarizing) 



Dep.] 



156 



LDev. 



Deposit, Black, Electro-Metallurgical 

— A crystalline variety of electro - 

metallurgical deposit. (See Deposit, Electro- 
Metallurgical^) 

Deposit, Crystalline, Electro-Metallurgi- 
cal A non-adherent, non-coherent 

film of electrolytically deposited metal. (See 
Deposit, Electro-Metallurgical) 

Deposit, Electro-Metallurgical 

The deposit of metal obtained by any electro- 
metallurgical process. 

To obtain a good metallic deposit the density 
of the current must be regulated according to the 
strength of the metallic solution employed. 

Electro -metallurgical deposits are either — 

(i.) Reguline, or flexible, adherent and strongly 
coherent metallic films, deposited when neither 
the current nor the solution is too strong; or, 

(2.) Crystalline/ or non-adherent and non-co- 
herent deposits. 

The crystalline deposit may either be of a loose, 
sandy character, which is thrown down when too 
feeble a current is used with too strong a metallic 
solution, or it may consist of a bl ick deposit, which 
is thrown down when the current is too strong as 
compared with the strength of the solution. This 
latter character of deposit is sometimes technically 
called burning, and takes place most frequently 
at sharp corners and edges, where the current 
density is greatest. (See Current Density.') 

Deposit, Electro-Metallurgical Nodular 

A coherent, irregular electro-metal- 
lurgical deposit which occurs whenever the 
current density falls below its normal value. 
Deposit, Electro-Metallurgical, Reguliue 

A flexible, adherent and strongly 

coherent film of metal electrolytically de- 
posited. (See Deposit, Electro-Metallur- 
gical)) 

Deposit, Electro-Metallurgical, Sandy 

A non-coherent electro-metallurgical 

deposit which occurs whenever the current 
density exceeds its normal value. 
Depositing Cell. — (See Cell, Depositing) 
Depositing Tat.— (See Vat, Depositijig) 
Deposition, Electric The deposit- 
ing of a substance, generally a metal, by 
the action of electrolysis. (See Electrolysis) 



The electric deposition of a metal on any con» 
ducting surface is sometimes called an electro- 
metallurgical deposition. (See Metallurgy, 
Electro. ) 

Deprez-d' Arson val Galvanometer. —(See 

Galvanometer ; Deprez-d 'Arsonval.) 

Derivative Circuit— (See Circuit, De- 
rivative) 

Derived Circuit.— (See Circuit, Derived) 
Derived Units.— (See Units, Derived) 
Destructive Distillation.— (See Distilla- 
tion, Destructive) 

Detector Galvanometer. — (See Galva- 
nometer, Detector) 

Detector, Ground In a system 

of incandescent lamp distribution, a device 
placed in the central station, for showing by 
the candle-power of a lamp the approximate 
location of a ground on the system. 

Fig. 196, shows a form of ground -detector, in 




Fig, tq6. Ground- Detector ■, 

which a small transformer is placed on a board in 
connection with a lamp and a two-way switch. 
One terminal of the primary of the transformer is 
put to ground, while the other can be connected 
by means of the switch to one or the other of the 
two primary mains of the distribution circuit. 
Should an earth exist on either main, then when 
the testing transformer has its pole connected to 
the other main, the lamp in its secondary circuit 
will light up, providing the leak is of sufficient 
magnitude to permit a sufficiently great current 
to pass through the primary circuit. 

Detorsion Bar. — (See Bar, Detorsion.) 

Device, Electro-Receptive Various 



Dev.] 



157 



[Dey. 



devices placed in an electric circuit, and 
energized by the passage through them of the 
electric current. 

A translating device. 

The following are among the more important 
electro -receptive devices, viz. : 

(I.) Electro magnets. 

(2.) Electric motors. 

(3.) Electro-magnetic signal apparatus. 

(4.) Telegraphic or telephonic apparatus. 

{5.) An arc or incandescent lamp. 

(6.) An electric heater. 

{7.) A plating bath or voltameter. 

(8.) An uncharged storage cell. 

1(9.) A converter or transformer. 

Electro-Receptive Devices. 
Motion Reproduced. 
{!.) Electric motor. 
(2.) Telpherage system. 
(3.) Telephone receiver. 
{4.) Telegraphic apparatus. 
(5.) Telephote receiver. 

Radiant Energy Produced, 
(6.) Arc or incandescent electric lamp. 
(7.) Electric heater. 
(8.) Electric welder. 
(9.) Leyden jar or battery. 

Chemical Decomposition Effected. 
(10.) Electrolytic bath. 
(II.) Uncharged storage battery. 

Electro -Magnetism Produced. 
^12.) Electro-magnet. 
Device, Feeding, of an Arc Lamp . — 



A device for maintaining the carbon electrodes 
of an arc lamp at a constant distance apart 
during their consumption. (See Lamp, 
Electric Arc.) 

Device, Magneto-Receptive —Any 

device that is capable of being energized 
when placed in a magnetic field. 

The term magneto-receptive device is used in 
contradistinction to electro-receptive device. (See 
Device, Electro- Receptive.) 

Device or Arrangement, Electromotive 

A term sometimes employed instead 

of an electric source. (See Source, Electric. 
Arrangement or Device, Electromotive.) 



Device, Safety, for Arc Lamps, or Series 
Circuits Any mechanism which auto- 
matically provides a path for the current 
around a lamp, or other faulty electro-recep- 
tive device in a series circuit, and thus pre- 
vents the opening of the entire circuit on the 
failure of such device to operate. (See Lamp, 
Electric Arc.) 

Device, Safety, for Multiple Circuits 

— A wire, bar, plate or strip of readily 
fusible metal, capable of conducting, without 
fusing, the current ordinarily employed on the 
circuit, but which fuses and thus breaks the 
circuit on the passage of an abnormally great 
current. 

The terms safety-catch, safety-plug, safety- 
strip and safety -fuse are also used for this safety 
device. (See Fuse, Safety.) 

Device, Translating — A term em- 
bracing electro-receptive and magneto-recep- 
tive devices. (See Device, Electro-Recep- 
tive.) 

Translating devices are placed in an electric 
circuit, and when traversed by the current effect 
a change, or translation in the form of the electric 
energy whereby useful work is accomplished. 

Translating devices depend for their operation 
on the luminous, heating, magnetic, or chemical 
effects of the current. 

Devices, Electro-Receptive, Multiple- 
Connected — A connection of electro- 
receptive devices, in which the positive poles 
of a number of separate devices are all con- 
nected with a single positive lead or conduc- 
tor, and the negative poles all connected with 
a single negative lead or conductor. 

The multiple-arc-connection of electro-receptive 
devices is suitable for constant potential circuits^ or 
those in which the electromotive force is main- 
tained approximately constant In such circuits 
the energy absorbed by each device will increase 
as its resistance decreases, since the energy ab- 
sorbed is proportional to the current passing. 
(See Circuits, Varieties of.) 

Multiple-arc-connected electro-receptive devices 
are employed m incandescent lamp distribution. 
Each device added reduces the resistance of the 
entire circuit. 



Dev.] 



158 



[Dia. 



Devices, Electro-Receptire,Multiple- Arc- 
Connected ■ — A term used in place of 

multiple-connected electro-receptive devices. 
(See Devices, Electro-Receptive, Multiple- 
Connected.) 

Devices, Electro-Receptive, Multiple- 

Series-Connected A connection of 

electro-receptive devices in which a number of 
separate electro-receptive devices are con- 
nected in groups in series, and each of these 
separate groups afterwards connected in mul- 
tiple-arc. 

The multiple-series connection permits electro- 
receptive devices to be placed on mains whose 
electromotive force would be too high to permit 
a single service to be connected directly to them. 
It is of great value in the distribution of incandes- 
cent lamps by constant currents, since by per- 
mitting a higher electromotive force to be em- 
ployed on the main conductors, it reduces the 
dimmsions of the conductors required for the 
economical distribution of the current. (See 
Circuits, Varieties of.) 

Devices, Electro-Receptive, Series-Con- 
nected The connection of electro- 
receptive devices in which the devices are 
placed consecutively in the circuit, so that the 
current passes successively through all of 
them from the first to the last. 

The series-connection of electro-receptive de- 
vices is suited to constant -current circuits. The 
work done in the device is developed by the fall 
of potential in each device. This kind of con- 
nection is used in most systems of arc light and 
telegraphic lines. (See Circuits, Varieties of.) 

Devices, Electro-Receptive, Series-Mul- 

tiple-Connected — A connection of 

electro-receptive devices in which a number 
of separate electro-receptive devices are joined 
in separate multiple groups, and each of these 
groups subsequently connected with one an- 
other in series. 

The effect of series-multiple connections is to 
split up the current into a number of separa.e 
currents of smaller strength, but of the same 
electromotive force. It is applicable to such cases 
as the combination of arc and incandescent lamps 
in the same circuit. (S?e Circuits, Varieties of ) 

Devices, Translating, Multiple-Con- 



nected A term sometimes used for 

multiple-connected electro-receptive devices. 
(See Devices, Electro-Receptive, Multiple' 
Connected') 

Devices, Translating, Multiple-Arc-Con- 
nected — A term used in place of 

multiple-connected electro-receptive devices. 
(See Devices, Electro-Receptive, Multiple- 
Connected) 

Devices, Translating-, Multiple-Series- 
Connected — A term sometimes used 

instead of multiple-series-connected electro- 
receptive devices. (See Devices, Electro- 
Receptive, Multiple-Series-Connected) 

Devices, Translating, Series-Connected 
A term sometimes used for series- 
connected electro-receptive devices. (See 
Devices, Electro - Receptive, Series - Con- 
nected) 

Devices, Translating, Series-Multiple* 

Connected A term sometimes used 

for series-multiple-connected electro-recep- 
tive devices. (See Devices, Electro-Recep- 
tive, Series-Multiple- Connected) 

Dextrorsal Helix. — (See Helix, Dex- 
trorsal) 

Dextrorsal Solenoid. — (See Solenoid, Dex- 
trorsal) 

Diacritical Current. — (See Current, Dia- 
critical) 

Diacritical Number. — (See Number, Dia- 
critical) 

Diacritical Point of Magnetic Satura- 
tion. — (See Saturation, Magnetic, Diacrit- 
ical Point of) 

Diagnosis, Electro. — Diagnosis by means 
of the exaggeration or diminution of the re- 
action of the excitable tissues of the body 
when subjected to the varying influences of 
electric currents. 

The electric current has also been applied in 
order to distinguish between forms of paralysis, 
and as a final test of death. 

Diagnostic, Electro Pertaining to 

electro-diagnosis. (See Diagnosis, Electro) 

Diagometer, Rousseau's An ap- 
paratus in which an attempt is made to 



Dia.] 



15 l J 



[Dia. 



determine the chemical composition and con- 
sequent purity of certain substances by their 
electrical conducting powers. 

The arrangement of the apparatus is shown in 
Fig 197. A dry pile. A, has its negative, or — 




Fig. IQ7 Rousseau's Diagometer. 

terminal, m', grounded. Its positive, or -f- ter- 
minal is connected to a delicately supported, and 
slightly magnetized needle, M, terminated by a 
conducting plate, L. Opposite L, and at the same 
height, is a fixed plate of slightly larger size. The 
needle M, when at rest in the plane of the magnetic 
meridian, is in contact at L, with the fixed plate. 
If, therefore, the upper plate of the pile is con- 
nected with the needle M, both plates arc, similarly 
charged and repulsion takes place, the needle 
coming to rest at a certain distance from the fixed 
plate. 

The substance whose purity is to be determined 
is placed in the cup G, which is connected, 
through L, with the fixed plate, A branch wire 
from the -J- terminal of the pile is then dipped into 
the substance in G, and its purity determined 
from the length of time required for the two plates 
at L, to be discharged through the material in G, 

It is claimed that the instrument will detect the 
difference between pure coffee and chicory . Its 
practical application, however, is very doubtful. 

Diagram, Thermo Electric —A 

diagram in which the thermo-electric power 
between different metals is designated for 
different temperatures. 

The differences of potential, produced by the 
mere contact of two metals, varies, not only with 
the kind of metals, and the physical state of each 
metal, but also with their temperature. This 
difference of potential, maintained in conse- 
quence of the difference of temperature between 
the junctions of a thermo-electric couple, is ap- 
proximately proportional to the differences of 
temperature of these junctions, if these differences 
are not great, and is equal to the product of such 





























Lead 






A 








B 


-Copper. 


~^fr 














V9^ 








B' 










A 












^-^ 



















differences of temperature and a number depend ent 
on the metals in the couple. This number is 
called the thermo-electric power. (See Couple, 
Thermo-Electric. Thermo-Electric Power.) 
In Fig. 198 (after Tait), the thermo-electric 

0°e 60°£ 100°<; YM°c 200"c 250°c 3<X)°c 350°c 400°c 450°c 



1500 
1734 

Fig. ig&. Thermo-Electric Diagram. 
power is shown between lead and iron, and lead 
and copper. The numbers at the top of the table 
represent degrees of the centigrade thermometer. 
Those at the sides represent the differences of 
potential in micro -volts. 

The thermo-electric power of the copper-iron 
couple decreases from the freezing point of water, 
O degrees C, to a temperature of 274.5 degrees 
C, when it becomes zero. Beyond that temper- 
ature the thermo-electric power increases, but in 
the opposite direction. The point at which this 
occurs is called the neutral point. 

Dial Telegraph. — (See Telegraphy, Dial.) 

Dialysis. — The act of separating a mixture 
of crystalloids and colloids by diffusion 
through a membrane. 

If, for example, the contents of a stomach, in a 
case of suspected poisoning, be placed in a vessel, 
the bottom of which is formed of a sheet of 
parchment paper and floated in water, the 
crystalloid or substances capable of crystalliz- 
ing, will pass into the water and the colloid, an 
uncrystallized jelly-like substance, will remain in 
the vessel. This process has been used to detect 
the presence of poison in the stomach in post- 
mortem cases. 

Diamaguetic. — The property possessed by 
substances like bismuth, phosphorus, anti- 
mony, zinc and numerous others, of being 
apparently repelled when placed between the 
poles of powerful magnets 

When diamagnetic substances in the form of 
rods or bars are placed, as in Fig. 199, between 
the poles of a powerful electro-magnet, they 
place themselves at right angles to the poles, or 
are apparently repelled. 

Paramagnetic substances like iron or steel, on 
the contrary, come to rest under similar circum- 



Dia.] 



160 



[Dia. 



stances in a straight line joining the poles, at 
right angles to the position shown in Fig. 199. 

Paramagnetic substances are sometimes called 
ferro-magnetic, or substances magnetic after the 
manner of iron. This word is unnecessary and 
ill-advised. The term sidero -magnetic, which has 
also been proposed in place of paramagnetic, is 
also unnecessary. 

Paramagnetic substances appear to concentrate 
the lines of magnetic force on them ; that is, their 
magnetic resistance is 
smaller than that of the 
air or other medium in 
which the magnet is 
placed. They, there- 
fore, come to rest with 
their greatest dimen - 
sions in the direction of 
the lines of magnetic 
force. 

Diamagnetic sub- 
stances appear to have 
a greater magnetic re- 
sistance than that of 
the air around them. 
They, therefore, come 
to rest with their least 
dimensions in the direction of the lines of mag- 
netic force. 

The difference between paramagnetic and dia- 
magnetic substances is generally believed to be 
due to the varying resistance these substances 
thus offer to lines of magnetic force as compared 
with that offered by air or by a vacuum. 

Tyndall comes to the conclusion as the result of 
extended experimentation: * 4 That the diamag 
netic force is a polar force, the polarity of dia- 
magnetic bodies being opposed to that of para- 
magnetic ones under the same conditions of 
excitement." 

This view, however, is not generally accepted 
by scientists. 

Diamagnetism is also possessed by certain liquid 
and gaseous substances. 




Fig. iqq Effect of Para- 
magnetism , 



Diamagnetic 

Diamagnetic^) 



Polarity. — (See Polarity, 



Diainagnetically. — In a diamagnetic man- 
ner, 

Diamagnetism. — A term applied to the 
magnetism of diamagnetic bodies. (See Dia- 
magnetic^) 



Diamagnetism, Weber's Theory of ■ 

—A theory to account for the phenomena 
of diamagnetism. 

Weber's theory of diamagnetism, like Ampere's 
theory of magnetism, supposes that magnetic 
substances consist of originally magnetized mole- 
cules or atoms, and that the act of magnetization 
consists of polarizing these atoms or molecules, 
or turning them in one and the same direction. 
That the original condition of the molecules or 
atoms is probably due to the passage of electricity, 
which continually circulates through their mass, 
the atoms being supposed to possess perfect con- 
ductivity. 

Suppose the substance through whose mole- 
cules or atoms these currents are flowing be 
immersed in a magnetic field. All of the mole- 
cules or atoms which can turn so as to look along 
lines of force in the right direction will have the 
current flowing in them thereby weakened so long 
as they remain in the field. When drawn out of 
it, however, these currents will regain their nor- 
mal strength. 

Suppose now the case of a substance, in which 
the currents are normal but weak, immersed in a 
strong magnetic field. There may thereby be 
effected a complete reversal of the direction of 
these currents, and others may be produced 
which flow in the opposite direction, and which 
will continue so to flow as long as the substance 
remains in the field. Such currents would then 
be sufficient to explain the phenomena of diamag- 
netic action. 

An electric current produced in a circuit near 
which a momentary current of electricity is sud - 
denly brought has now the opposite direction to 
that which produces it, and this momentary cur- 
rent would tend to produce repulsion. When, 




Fig 200, Weber's Theory of Diamagnetism. 
too, the circuit is drawn out of the neighborhood 
in which another current is flowing, another mo- 



Dia.] 



161 



[Die. 



mentary current is produced in the same direc- 
tion. This produces attraction. 

Now, regarding the same phenomena from the 
standpoint of lines of magnetic force, when a 
conductor through which a current is passing is 
placed in a magnetic field, any increase in the 
number of lines of magnetic force passing through 
it tends to move the conductor out of the magnetic 
field, while any decrease in the number of lines 
of force tends to move the conductor into the 
field. To experimentally show the attractions 
and repulsions produced by magnetization or 
demagnetization, the following apparatus may be 
employed: 

A stout disc of copper, Fig. 200, is supported 
on a horizontal arm in the position shown in front 
of the pole of a powerful electro- magnet. When 
the curre it is sent through the electro-magnet the 
disc of copper is repelled from the magnetic pole. 
When the magnetism is being destroyed by the 
opening of the circuit and by the weakening of 
the current, the copper disc is attracted. 

Diamagnetometer. — An apparatus de- 
signed for studying diamagnetism. (See Dia- 
magnetism. ) 

The apparatus for the study of paramagnetism 
generally receives simply the name of magnet- 
ometer. 

Diamagnets. — Diamagnetic substances 
subjected to magnetic induction and formerly 
called diamagnets in contradistinction to or- 
dinary magnets. 

Diamagnets are supposed by some to possess a 
polarity the same as that of the inducing pole, 
instead of the opposite polarity, as in paramagnetic 
substances. (See Diamagnetism.) 

Diaphragm. — A sheet of some solid sub- 
stance, generally elastic in character and cir- 
cular in shape, securely fixed at its edges and 
capable of being set into vibration. 

The receiving diaphragm of a telephone is 
generally a thin plate or disc of iron, fixed at its 
edges, placed near a magnet pole and set into 
vibration by variations in the magnetic strength 
of the pole, due to variations in the current that 
is passed over the line. 

The transmitting diaphragm of the telephone 
or of a phonograph, consists of a plate fixed at its 
edges and set into vibration by the sound waves 
striking it. 



Diaphragm. — A term sometimes employed 
for a plate form of porous cell. 

Diaphragm Currents.— (See Currents, 
Diaphragm. Cell, Porous) 

Diaphragm of Yoltaic Cell. — A term 
sometimes used for the porous cell of a 
double fluid voltaic cell when in the form of 
a plate. 

Dice-Box Insulator. — (See Insulator, 
Dice-Box) 

Dielectric. — A substance which permits 
induction to take place through its mass. 

This word is sometimes, but improperly, writ- 
ten Di- Electric. 

The substance which separates the opposite 
coatings of a condenser is called the dielectric. 
All dielectrics are non-conductors. 

All non-conductors or insulators are dielectrics, 
but their dielectric power is not exactly propor- 
tional to their non-conducting power. 

Substances differ greatly in the degree or ex- 
tent to which they permit induction to take place 
through or across them. Thus, a certain amount 
of inductive action takes place between the insu- 
lated metal plates of a condenser across the layer 
of air between them. 

A dielectric may be regarded as pervious to 
rapidly reversed periodic currents, but opaque to 
continuous currents. There is, however, some 
conduction of continuous currents. 

According to Swinburne, there are three species 
of conduction that may take place in < lelectrics, 
all of which produce a heating of the dielectric, 
viz.: 

(i.) Metallic Conduction, i. e., such a conduc- 
tion as takes place in a metal. This kind of con- 
duction arises from the presence of metallic par- 
ticles embedded in the dielectric. 

(2.) Disruptive Conduction, or a momentary 
current accompanying a disruptive discharge. 

(3.) Electrolytic Conduction, or that kind of 
conduction which accompanies the electrolysis 
of a conductor. This kind of conduction may 
take place in some kinds of glass. 

Faraday regarded the dielectric as the true seat 
of electric phenomena. Conducting substances 
he considered as mere breaks in the continuity of 
the dielectric. This is the view now generally 
held. 

Dielectric Capacity.— (See Capacity, Di- 
electric) 



Die. 



162 



[Dim, 



Dielectric Constant. — (See Constant t 
Dielectric) 
Dielectric Density of a Gas. — (See Gas, 

Dielectric Density of) 
Dielectric, Polarization of — A 

molecular strain produced in the dielectric of a 
Leyden jar or other condenser, by the attrac- 
tion of the electric charges on its opposite 
faces, or by the electrostatic stress. (See 
Strain, Dielectric) 

A term formerly employed in place of 
electric displacement. 

Faraday, in his study of the action of induction, 
in denying the possibility of action at a distance, 
thought that the dielectric through which induc- 
tion takes place was polarized, and that in this 
way the induction was transmitted across the 
intervening space between the inducing and the 
induced body, by the action of the contiguous 
particles of the dielectric. 

The polarization of the glass of a Leyden jar, 
and the accompanying strain, are seen by the 
frequent piercing of the glass, and by the 
residual charge of the jar. (See Charge, Resid- 
ual.} 

Dielectric Resistance.— (See Resistance.. 
Dielectric.) 

Dielectric Strain. — (See Strain, Dielec- 
tric) 

Dielectric Strength of a Gas.— (See Gas, 
Dielectric Strength of) 

Dielectric Stress. — (See Stress, Dielec- 
tric) 

Difference of Potential.— (See Potential, 
Difference of) 

Differential Electric Bell.— (See Bell, 
Differential Electric) 

Differential Galvanometer. — (See Gal- 
vanometer, Differential) 

Differential Inductometer.— (See Tnduc- 
tometer, Differential) 

Differential Method of Duplex Teleg- 
raphy. — (See Telegraphy, Duplex, Differ- 
ential Method of) 

Differential Relay. — (See Relay, Differ- 
ential) 

Differential Thermo-Pile.— (See Pile, 
Thermo, Differential) 



Differential Voltameter.— (See Voltam- 
eter, Siemens' Differential) 

Differentially Wound Motor. — (See 

Motor Differentially Wound.) 

Diffusion, Anodal A term applied 

to the introduction of any drug into the human 
body by electricity. 

The cataphoretic introduction of drugs 
into the body. (See Cataphoresis) 

A sponge or other similar electrode, saturated 
with a solution of the drug, is connected with 
the anode of a source and placed over the part 
to be treated and its kathode connected to 
another part of the body in a nearly direct line 
with the anode and the current parsed, 

Diffusion Creep. — (See Creep Diffusion) 

Diffusion of Electric Current. — (See 
Current, Diffusion of) 

Diffusion of Lines of Force.— (See Force, 
Lines of Diffusion of) 

Dimensions of Acceleration.— (See Ac* 
celeration, Dimensions of.) 

Dimensions of Units — (See Units, Dimen* 
sions of) 

Diminished Electric Irritability. — (See 
Irritability , Electric, Diminished.) 

Dimmer A choking coil, employed 

in a system of distribution by converters or 
transformers, for regulating the potential of 
the feeders. 

The dimmer consists essentially of a choking 
coil wound around a laminated ring of soft iron, 




Fig. 20 T. Reaction Coil Dimmer. 

and provided with an envelope of heavy copper. 
The copper ring, by its position as regards the 
choking coil, adjusts or regulates the self-induc- 
tion of the coil, and consequently regulates the 
potential of the feeders. The dimmer is used in 
theatres or similar situations to turn the lights up 
or aown. 



Die] 



163 



[Dip. 



The reaction coil or dimmer is shown in Fig. 
201. The choking coil is wound on a ring of 
iron. The copper sheath is furnished with a 
handle to permit its position to be readily- 
changed with respect to the coil of insulated wire. 
A laminated iron drum is supported on bearings 
inside the ring. When the sheath is over the 
coil, the coil offers but a small resistance to the 
passage of the current. When away from it the 
self-induction of the coil is increased. 

Dioptre. — A unit of refracting power. 

A lens of one dioptre has a focal length of 
one metre. One of two dioptres has a focal 
length of 50 centimetres; one of four dioptres 
25 centimetres. This is also spelled dioptry. 

Dioptric. — Relating to dioptrics. 
Dioptrics. — The science which treats of 
the refraction of light. 

Dioptry. — A word sometimes used for di- 
optre. (See Dioptre?) 

Dip, Magnetic The deviation of a 

magnetic needle from a true horizontal posi- 
tion. 

The inclination of the magnetic needle to- 
wards the earth. 

The magnetic needle shown in Fig. 202, though 




20 2. Angle 0/ Dip. 



supported at its centre of gravity, will not retain 
a horizontal position in all places on the earth's 
surface. 



In the northern hemisphere its north-seeking 
end will dip or incline at an angle B O C, called 
the angle of dip. In the southern hemisphere 
its south seeking end will dip. 

The cause of the dip is the unequal distance of 
the magnetic poles of the earth from the poles of 
the needle. 

The magnetic equator is a circle passing 
around the earth midway (in intensity) between 
the earth's magnetic poles. There is no dip at 
the magnetic equator. At either magnetic pole 
the angle of dip is 90 degrees. 

Dip, or Inclination, Angle of 

The angle which a magnetic needle, free to 
move in both a vertical and a horizontal plane, 
makes with a horizontal line passing through 
its point of support. 

The angle of dip of a magnetic needle. 
(See Inclination, Angle of.) 

Diplex Telegraphy. — (See Telegraphy, 
Diplex?) 

Dipping. — An electro-metallurgical process 
whereby a deposit or thin coating of metal 
is obtained on the surface of another metal 
by dipping it in a readily decomposable 
metallic salt. 

Cleansing surfaces for electro-plating pro- 
cesses by immersing them in various acid 
liquors. 

Dipping, Bright Dipping in acid 

liquors for the purpose of obtaining a bright 
electro-metallurgical coating. 

Dipping Circle. — (See Circle, Dipping?) 

Dipping, Dead ■ — Dipping in acid 

liquors for the purpose of obtaining a dead or 
unpolished surface on an electro-metallurgical 
coating. 

Dipping, Electro-Metallurgical — 

A process for obtaining an electro-metallur- 
gical deposit on a metallic surface by dipping 
it in a solution of a readily decomposable 
metallic salt. 

A bright, polished iron surface, when simply 
dipped into a solution of copper-sulphate, re- 
ceives a coating of metallic copper from the elec- 
trolytic action thus set up. 

This process is known technically as dipping. 
The term dipping is also used in electro- metal- 
lurgy to indicate the process of cleaning the 



Dir.] 



164 



[Dis. 



articles, that are to be electro-plated, by dipping 
them in various acid or alkaline baths. 

Direct Current. — (See Current, Direct^ 
Direct-Current Electric Motor. — (See 
Motor, Electric, Direct-Current?) 

Direct Electromotive Force. — (See Force, 
Electromotive, DirectX) 

Direct Excitation. — (See Excitation, 
Direct?) 

Direct-Induced Current. — (See Current, 
Direct-Induced.) 

Direct, or Break-Induced Current 

— (See Current, Direct. Current, Break- 
Induced.) 
Direct Working. — (See Working, Direct.) 
Direction, Negative, of Electrical Con- 

yection of Heat A direction in which 

heat is transmitted through an unequally 
heated conductor by electric convection, 
during the passage of electricity through the 
conductor, opposite that of the current. (See 
Heat, Electric Convection of.) 

Direction of Lines of Force. — (See Force, 
Lines of, Direction of.) 
Direction, Positive, of Electrical Con- 

Tection of Heat A direction in 

which heat is transmitted through an un- 
equally heated conductor by electric convec- 
tion, during the passage of electricity through 
the conductor, the same as that of the cur- 
rent. (See Heat, Electric Convection of.) 
Direction, Positive, Bound a Circuit 

In a plane circuit looked at from 

one side, a direction opposite to that of the 
hands of a clock. 

This is a convention which has been made in 
order to conveniently connect the direction of the 
electromotive force produced by induction, with 
the direction of the induction. 

Direction, Positive, Through a Circuit 

In a plane circuit, looked at from 

one side, a direction through the circuit away 
from the observer. 

Directive Tendency of Magnetic Needle. 
— (See Needle, Magnetic, Directive Ten- 
dency of.) 

Disc, Arago's A disc of copper 



or other non-magnetic metallic substance, 
which, when rapidly rotated under a mag- 
netic needle, supported independently of the 
disc, causes the needle to be deflected in the 
direction of rotation, and, when the velocity 
of the disc is sufficiently great, to rotate with it. 
Such disc is shown in Fig. 203 at b. The move- 




Fig. 203. Arago's Disc. 

ment of the needle is due to electric currents, in- 
duced by the disc moving through the field of the 
needle so as to cut its lines of magnetic force. To 
obtain the best results the disc must move very 
rapidly, and should be near the needle. More- 
over, the needle should be powerful. 

This effect was discovered by Arago, in 1824. 
Since a magnetic needle moving over a metallic 
plate produces electric currents in a direction 
which tends to stop the motion of the needle, a 
damping of the motion of a magnetic needle is 
sometimes effected by causing it to move near a 
metal plate. The induced currents, which the 
needle produces in the plate by its motion over it, 
tend to retard the motion of the needle. (See 
Damping. Law, Lenz's.) 

Disc Armature. — (See Armature, Disc.) 

Disc, Faraday's ■ — A metallic disc 

movable in a magnetic field on an axis, 
parallel to the direction of the field. 

Such a disc is shown in Fig. 204, and moves,- 



dS^ 




Fig. 204. Faraday's Disc. 

as will be seen, so as to cut the lines of magnetic 
force at right angles. 

The difference of potential generated by the 
motion of such a disc may be caused to produce 
a current, by providing a circuit which is com- 
pleted through the portion of the disc that at any/" 



Dis.] 



165 



[Dis. 



moment of its rotation is situated between spring 
contacts resting on the axis of rotation and the 
circumference of the disc, respectively. 

In Barlow s or Sturgeon' 's wheel, Fig. 205, the 




Fig. 203. Barlow's Wheel. 

wheel itself rotates in the direction shown, when 
a current is sent through it in a direction indicated 
by the arrows. 

Discharge. — The equalization of the dif- 
ference of potential between the terminals of 
a condenser or source, on their connection by 
a conductor. 

The removal of a charge from the surface 
of any charged conductor by connecting it 
with the earth, or another conductor. 

The removal of a charge by means of a 
stream of electrified air particles. 

The discharge of an insulated conductor, a 
cloud, a condenser, or a Leyden battery, is oscil- 
latory. The oscillatory currents continue but for 
a short time. The discharge is therefore often 
spoken of as producing momentary currents. 

The discharge of a voltaic battery, or a stor- 
age battery, is nearly continuous, and furnishes a 
current which is practically continuous, as dis- 
tinguished from the momentary currents produced 
by the discharge of a condenser. 

A discharge may be alternating, brush, brush 
and spray, conductive, convective, dead-beat, 
disruptive, flaming, glow, lateral, oscillatory, 
periodic, stratified, streaming, impulsive and 
periodic. 

Discharge, Alternating An elec- 
tric discharge which changes its direction at 
regular intervals of time. 

A periodic discharge. 

Discharge, Brush A faintly lu- 
minous discharge that occurs from a pointed 
positive conductor. 

The brush discharge is a species of convective 
discharge. In it, the streams of electrified air 
particles assume the characteristic brush shape. 
(See Discharge, Convective.) 



Discharge, Brush-and-Spray — A 

form of streaming discharge obtained by in- 
creasing the frequency of the alternations 
of a high potential current which assumes 
the appearance of a spray of silver-white 
sparks, or a bunch of thin silvery threads 
around a powerful brush. 

Some idea of the brush-and-spray discharge 
may be obtained from Fig. 206, taken from 




Fig. 206. Brush-and-Spray Discharge ( Tesla). 

Tesla, who has carefully studied these phenom- 
ena. 

The brush-and-spray discharge is best obtained, 
according to Tesla, by bringing the terminals 
of a source of rapidly alternating electrostatic 
currents of high potential somewhat nearer to- 
gether, when the streaming discharge has beert 
obtained, and preferably increasing the frequency 
of the alternations. 

The brush-and-spray discharge, when power- 
ful, closely resembles a gas flame from gas escap- 
ing under great pressure. Says Tesla: "But 
they do not only resemble, they are verita'le 
flames, for they are hot. Certainly they are not 
as hot as a gas burner, but they would be so if t he- 
frequency and the potential would be sufficiently 
high:' 

The brush-and-spray discharge, at higher fre- 
quencies, passes into a form of discharge for which 
Tesla has proposed no particular name. He de- 
scribes this form, in a publication of a lecture 
before the American Institute of Electrical Engi- 
neers, as follows, viz. : 

"If the frequency is still more increased, then 
the coil refuses to give any spark unless at com- 
paratively s/nall distances, and the fifth typical 
form of discharge may be observed (Fig. 207). 
The tendency to stream out and dissipate is then 
so great that when the brush is produced at one 
terminal no sparking occurs, even if, as I have re- 
peatedly tried, the hand, or any conducting ob- 
ject, is held within the stream ; and, what is more 



Dis.] 

singular, the luminous stream is not at all easily 
deflected by the approach of a conducting body. 

"At this stage the streams seemingly pass with 
the greatest freedom through considerable thick- 
nesses of insulators, and it is particularly interest- 
ing to study their behavior. For this purpose it 
is convenient to connect to the terminals of the 
coil two metallic spheres, which may be placed at 
any desired distance (Fig. 208) . Spheres are pref- 



166 



[Dis. 




Fifth, Typical Form of Discharge ( Tesla). 



erable to plates, as the discharge can be better 
observed. By inserting dielectric bodies between 
the spheres, beautiful discharge phenomena may 
be observed. If the spheres be quite close and a 
spark be playing between them, by interposing a 
thin plate of ebonite between the spheres the 
spark instantly ceases and the discharge spreads 
into an intensely luminous circle several inches in 
diameter, provided the spheres are sufficiently 
large. The passage of the stream heats, and, 
after a while, softens the rubber so much that two 




Fig. 208. 



Lu—iinous Discharge with Interposed 
Insulators. 



plates may be made to stick together in this man- 
ner. If the spheres are so far apart that no spark 
occurs, even if they are far beyond the striking 
distance, by inserting a thick plate of glass the 
discharge is instantly induced to pass from the 
spheres to the glass in the form of luminous 
streams. It appears almost as though these 



streams pass through the dielectric. In reality 
this is not the case, as the streams are due to the 
molecules of the air which are violently agitated 
in the space between the oppositely charged sur- 
faces of the spheres. 

" When no dielectric other than air is present, 
the bombardment goes on, but is too weak to 
be visible ; by inserting a dielectric the indue 
tive effect is much increased, and besides, the 
projected air molecules find an obstacle and the 
bombardment becomes so intense that the streams 
become luminous. If by any mechanical means 
we could effect such a violent agitation of the 
molecules we could produce the same phenom- 
enon. A jet of air escaping through a small 
hole under enormous pressure and striking 
against an insulating substance, such as glass, 
may be luminous in the dark, and it might be 
possible to produce phosphorescence of the glass 
or other insulators in this manner. 

" The greater the specific inductive capacity of 
the interposed dielectric, the more powerful the 
effect pioduced. Owing to this the streams show 
themselves with excessively high potentials even 
if the glass be as much as one and one-half to two 
inches thick. But besides the heating due to bom- 
bardment, some heating goes on undoubtedly in 
the dielectric, being apparently greater in glass 
than in ebonite. I attribute this to the greater 
specific inductive capacity of the glass in conse- 
quence of which, with the same potential differ- 
ence, a greater amount of energy is taken up in it 
than in rubber. It is like connecting to a battery 
a copper and a brass wine of the same dimen- 
sions. The copper W'.'re, though a more perfect 
conductor, would heat more by reason of its tak- 
ing more current. Thus what is otherwise con- 
sidered a virtue of the glass is here a defect. 
Glass usually gives way much quicker than ebo- 
nite ; when it is heated to a certain degree the 
discharge suddenly breaks through at one point, 
assuming then the ordinary form of an arc." 

Discharge, Conductive — A dis- 
charge effected by leading the charge off 
through a conductor placed in contact with 
the charged body. 

Discharge, Convectire — A dis- 
charge which occurs from the points on the 
surface of a highly charged conductor, 
through the repulsion by the conductor of air 
particles that in this manner carry off minute 
charges. 



Dis.] 



167 



[Dis. 



A corrective discharge, though often attended 
"by a feeble sound, is sometimes called a silent 
discharge, in order to distinguish it from the 
noisy, disruptive discharge, which is attended by 
a sharp snap, or when considerable, by a loud 
report. 

A convective discharge is also called a glow or 
Irtish discharge. The latter is best seen at the 
small button at the end of the prime or positive 
conductor of a frictional electric machine. 

The positive discharge from a point or small 
rounded conductor is always brush-shaped; the 
negative discharge is always star-shaped. 

In rarefied gases, the discharge is convective in 
character and produces various luminous effects 
of great beauty, the color of which depends on 
the kind of gas, and the size, shape and material 
of the electrodes, and on the degree of the vacuum. 
Thus in the rarefied 
space of the vessel shown 
in Fig. 209, the discharge 
becomes an ovoidal mass 
of light, sometimes called 
the Philosopher^ s Egg. 

When the discharges 
in rarefied gases follow 
one another very rapid- 
ly, alternations of light I 
and darkness, or stratifi- 
cations, or stria are pro- 
duced. 

The breadth of the 
dark bands increases as 
the vacuum becomes 
higher. The light por- 
tions start at the positive 
electrode, and are hotter 
than the dark portions. 

The effects of luminous 
convective discharges are 
best seen in exhausted g^ss tubes, called Geissler 
tubes, containing residual atmospheres of various 
gases. (See Tubes, Geissler.) 

Discharge, Dead-Beat — A non- 
oscillatory discharge. (See Discharge, 
Oscillatory?) 

Discharge, Disruptive A sudden, 

and more or less complete, discharge that 
takes place across an intervening non-con- 
ductor or dielectric. 

A mechanical strain of the dielectric occurs, 
which suddenly breaks down as it were and per- 




Fig. 209. Discharge in 
Rarefied Air. 



mits the discharge to pass as a spark, or rapid 
succession of sparks. 

In air, the spark, when long, generally takes 
the zigzag path, as shown in Fig. 210. 

The sparks produced by disruptive discharges 
consist of heated gases, 
together with portions of 
the conductor that are 
volatilized by the heat. 

The discharge of a Ley- 
denjar or condenser may 
be disruptive, as when 
the discharging rod is 
held with one knob con- 
nected with one coating, 
and the other near the 
other coating. It may 
be gradual, as when the 
two coatings are alter- 
nately connected with the 
ground. The discharge 
of a Leyden jar as, in- 
deed, the disruptive dis- 
charge in general, is os- 
cillatory. 

The stress is often suf- 
ficient to pierce the glass. 

Discharge, Dura- 
tion of — — —The 
time required to effect a complete disruptive 
discharge. 

The disruptive discharge is not instantaneous; 
some time is required to effect it. Estimates of 
the duration of a flash of lightning based on the 
duration of a Leyden jar discharge, are mislead- 
ing from the enormous difference in the quantity 
and the potential in the two cases. The fact that 
the disruptive discharge is oscillatory and consists 
of a number of discharges taking place in alter- 
nately opposite directions shows that the discharge 
is not instantaneous. 

Leyden jar discharges, are, however, accom- 
plished in very small periods of time. 

Discharge, Flaming — The white 

and flaming arc-like discharge that occurs 
between the terminals of the secondary of an 
induction coil, when, with a great number of 
alternations per second, the current through 
the primary is increased beyond that required 
for the sensitive-thread discharge. (See Dis- 
charge, Sensitive- Thread) 




Fig. 2 to. Disruptive 
Discharge. 



Bis.] 



168 



[Dis. 



According to Tesla the flaming discharge is 
best produced when the number of alternations is 
not too great and certain re ations between ca- 
pacity, self-induction and frequency are observed. 
These relations must be such as will permit the 
flow through the circuit of the maximum current, 
and thus may be obtained with wide variations in 
the frequency. The flaming discharge develops 
considerable heat, and is characterized by the 
absence of the shrill note accompanying less pow- 
erful discharges. This is probably due to the 
enormous frequency. 

Some idea of the flaming discharge may be had 




Fig. 211. Flaming Discharge {Tesla). 

from an inspection of Fig. 211, taken from Tesla. 

Discharge, Glow A form of con- 

vective discharge. (See Discharge, Con- 
nective.) 

Discharge, Impulsive A dis- 
charge produced in conductors by suddenly 
created differences of potential. 

Impulsive discharges are influenced more by the 
inductan ;e of a conductor than by its true ohmic 
resistance. (See Inductance. Resistance, Okmic.) 

A mass of guncottcm simply ignitad in the 
open air, produces but little effect on any resisting 
object placed below it. If, however, itbe rapidly 
ignited by means of a detonator, and is thus fired 
with much greater rapidity, it may shatter any- 
thing placed beneath it. 

In a sinilar manner, a rapidly discharged cur- 
rent, or impulsive discharge, produces, through the 
inductance of the conductor, a series of effects 
somewhat similar to the above, in which a great 
impedance is produced by a sudden change of 
direction. 

Discharge, Induced Currents, Effects 

Produced by — Varying classes of 

effects produced by the discharges of induced 
currents. 



The effects produced by discharges of induced 
currents are classified by Fleming as follows: 

(1.) Effects depending on the entire quantity of 
the discharge. 

a. Galvanometric effects. 

If the need'.e of the galvanometer has a period 
or time of oscillation that is long, as compared 
with the time of duration of the discharge, the sine 
of one-half the angle of deflection is proportionaL 
to the whole quantity of the discharge. 

b. Electro-chemical effects. 

The quantity of an electrolyte broken up is 
proportional to the quantity of electricity which 
passes through it. 

(2.) Effects depending on the average of the 
square of the current strength at any instant dur- 
ing the discharge. 

a. Heating effects. 

The rate of dissipation as heat, according to 
Joule's law, is proportional to the square of the 
current strength passing. 

b. Electro-dynamic effects. 

When a discharge passes through a circuit, 
part of which is fixed and part movable, the forces- 
of attraction and repulsion which take place be- 
tween t'.iem at any instant are proportional to 
the square of the current strength. 

(3.) Effects depending on rate of change of 
the current. 

a. Physiological effects. 

The effect of the discharge in producing physi- 
ological shock increases with the suddenness of 
the discharge. Of two discharges winch reached 
the same maxima that which reached it first would 
produce the greatest physiological effect. Recent 
investigations by Tesla and others would appear to 
partly disprove the above statement. 

b. Telephonic effects. 

The telephone, like the body of an animal, is 
affected more by the rate of change than by the 
current strength at any instant. 

c. Magnetic effects. 

Rayleigh has shown that the magnetic effects of 
the discharge depend upon the maximum current 
strength during the discharge, or upon the initial 
current strength, in cases where the current dies 
away gradually. Since the time required for the 
permanent magnetizing of a steel wire is small 
co npared with the duration of the induced cur- 
rent, the am ^unt of magnetism acquired depends 
essentially on the initial or maximum current 
strength during the discharge, irrespective of the 
time during which said discharge lasts. 



Dis.] 



169 



[Dis. 



d. Luminous effects. 

These are also dependent in the case of induced 
discharges on the rate of change of the current. 

Discharge-Key. — (See Key, Discharge.) 

Discharge, Lateral ■ — A discharge, 

taking place on the discharge of a Leyden jar, 
or other disruptive discharge, between parts 
of the jar or conductors, not in the circuit of 
the main discharge. 

If a charged Leyden jar is placed on an insulat- 
ing stool, and is then discharged by the discharg- 
ing rod, the lateral discharge is seen as a small 
spark that passes between the outside coating of 
the jar and a body connected with the earth at 
the moment of the discharge through the rod. 

A lateral discharge is also seen in the sparks 
that can be taken from a conductor in good con- 
nection with the earth, by holding the hand near 
the conductor, while it is receiving large sparks 
from a powerful machine in operation. These 
discharges are due to induction. 

If a Leyden jar be discharged by means of a con- 
ducting wire bent as shown in Fig. 212, in which 



t 



Fig. 212. 

two parts of the circuit are closely approached as at 
A, whenever a spark occurs at B, another spark 
produced by a lateral discharge occurs at A. 
Although the resistance of the metallic circuit is 
enormously less than the resistance of the air 
space through which the lateral discharge occurs, 
yet the counter electromotive force produced in 
the metallic circuit by the impulsive discharge, 
renders its resistance far greater than that of 
the air space. The path of a lateral discharge 
is called the alternative path. (See Path, Al- 
ternative. ) 

Discharge, Luminous Effects of 

The luminous phenomena attending and pro- 
duced by an electric discharge. 

The luminous effects vary as to color, intensity, 
shape and accompanying acoustic phenomena 
according to a variety of circumstances, the prin- 
cipal of which are as follows, viz. : 

(1.) With the kind of gaseous medium through 
which the discharge passes. Thus, a spark passed 
through hydrogen has a crimson or reddish color ; 



through carbonic acid or chlorine, a greenish 
color. 

(2.) With the density of the medium. In a 
partial vacuum, the discharge from an induction 
coil becomes an ovoidal mass of light. As the 
vacuum increases, the light at first grows brighter, 
but as a higher vacuum is reached, strise of al- 
ternate dark and light bands appear. Finally, 
with very high vacua the discharge fails to pass. 
(See Discharge, Convective. ) 

(3.) With the nature of the substances forming 
the points from which the discharge is taken. 
This is due to the partial volatilization of the ma- 
terial of the electrodes. 

(4.) With the kind of electricity, i. e., whether 
positive or negative. A positive charge assumes 
the shape of a fan; a negative discharge, that of 
a star. 

(5.) On the density of the discharge. The in- 
troduction of a Leyden jar or condenser in the 
circuit of a Holtz machine, for example, causes 
the spark to change from the faint bluish to the 
silvery white. 

(6.) The disruptive discharge through air is at- 
tended by snapping or crackling sound, which, in 
the case of lightning, reaches the intensity of thun- 
der. When the disruptive discharge takes place 
through a vacuum a faint hissing sound is heard, 
or all sound may entirely disappear. 

(7.) Luminous effects resulting from molecular 
bombardment occurring in co nparatively high 
vacua. These luminous effects may result : 

(a.) From actual incandescence of some refrac- 
tory material produced by the blows of the mole- 
cules; or, 

(b.) As a result of phosphorescence or fluores- 
cence due to such blows. 

Canary glass, or glass stained by uranium oxide, 
fluoresces and emits a yellowish green light; solu- 
tion of sulphate of quinine emits a bluish light. 

Discharge, Non-Oscillatory — A 

dead-beat discharge. (See Discharge, Dead- 
Beat.) 



Discharge, Oscillating 



-A number 



of successive discharges and recharges which 
occur on the disruptive discharge of a Leyden 
jar, or condenser. 

A discharge which periodically decreases 
by a series of oscillations. 

A discharge which produces a dying-away- 
backwards and forwards current. 



Dis.] 



170 



Dis, 



The disruptive discharge of a Leyden jar, or 
condenser, is not effected by a single rush of elec- 
tricity. When discharged through a compara- 
tively small resistance, a number of alternate 
partial discharges and recharges occur, which 
produce true oscillations or undulaiory discharges. 

These oscillations are caused by the induction 
of the discharge on itself, and are similar to the 
self-induction of a current. 

The existence of the oscillating discharge in the 
case of a Leyden jar or condenser, proves, in the 
opinion of some, that electricity, taken along 
with matter, possesses a property similar to 
inertia. 

Discharge, Oscillatory A term 

sometimes used for an oscillating discharge. 
(See Discharge, Oscillating) 

Discharge, Periodic — An electric 

discharge which changes its direction at reg- 
ular intervals or periods. 

An alternating discharge. 

Discharge, Periodically-Decreasing 

— An oscillating discharge whose decrease is 
periodic. (See Discharge, Oscillating) 

Discharge, Sensitive-Thread The 

thin, thread-like discharge that occurs be- 
tween the terminals of the secondary of an in- 
duction coil of high frequency. 

The sensitive-thread discharge occurs, accord- 
ing to Tesla, when the number of alternations per 




Fig. 213. Sensitive- Thread Discharge ( Tesla). 

second is high and the current through the 
primary small. This discharge has the form of 
a thin, feebly -colored thread. Though very sensi- 
tive, being deflected by a mere breath, it is never- 
theless quite persistent, if the terminals be at 
one-third of the striking distance apart. Tesla 
ascribes its extreme sensitiveness, when long, to 
the motion of suspended dust particles in the air. 
The general appearance of the sensitive-thread 
discharge is shown in Fig. 213, taken from Tesla. 



Discharge, Silent A name given 

to a convective discharge in order to distin- 
guish it from the more noisy disruptive dis- 
charge. 

The convective discharge in reality is attended 
by a feeble sound, which, however, is quiet when 
compared with the more pronounced sound of the 
disruptive discharge. (See Discharge, Convec- 
tive.) 

Discharge, Stratified The form 

of alternate light and dark spaces assumed by 
the discharges of an induction coil through a 
partially exhausted gas. (See Tube, Strati- 
Jication.) 

The striee are explained by Curtis as follows: 
"Under the influence of the electric rhythm of 
the rapidly following discharges the molecules 
of the residual gas collect in alternately dense 
and rarefied spaces. The light bands correspond to 
the spaces where the molecules are comparatively 
crowded together, and their concomitant friction 
produces the luminous disturbance. The dark 
spaces are where the molecules are further apart, 
and where their collisions are consequently less 
frequent. ' ' 

Discharge, Streaming A form as- 
sumed by the flaming discharge between the 
terminals of the secondary of an induction 
coil when the frequency of the alternations 
increases beyond a certain limit, and the 
potential has consequently increased. 

The streaming discharge partakes of the general 
characteristics of the flaming discharge. Lumi- 
nous streams pass in abundance, not only between 
the terminals of the secondary, but, according to> 
Tesla, who has carefully studied these phe- 
nomena, between the primary and the secondary, 
through the insulating dielectric separating 




Fig. 214. Streaming Discharge {Tesla). 

them. The streams not only pass between the 
terminals, but also issue from all points and pro- 



Dis, 



171 



LDis. 



jections, as will be seen from Fig. 214, taken from 
Tesla. 

When the streaming discharge reaches a cer- 
tain higher limit it "becomes a brush-and- spray 
discharge. (See Discharge, Brush-and- Spray .) 

The streaming discharge obtained from an in- 
duction coil with high frequencies differs from that 
of an electrostatic machine in that it neither pos- 
sesses the violet color of the positive static dis- 
charge nor the brightness of the negative, but is 
intermediate in color. 

Discharge, Surging — 



-A term some- 
times applied to an oscillatory discharge. (See 
Discharge, Oscillatory?) 

Discharge, to Electrically —To 

equalize differences of potential by connecting 
them by means of a conductor. 

Discharge, Undulatory — A dis- 
charge, the strength and direction of which 
gradually change. (See Currents, Undu- 
latory?) 

Discharge, Unidirectional — An 

electric discharge which takes place from the 
beginning to the end, in one and the same di- 
rection. 

The time 



Discharge, Telocity of 



required for the passage of a discharge 
through a given length of conductor. 

According to modern views it is the ether sur- 
rounding the wire or conductor which conveys 
the electric pulses. All the energy which gets into 
the conductor is dissipated as heat. 

The velocity of propagation of discharge of the 
pulses produced by the oscillating discharge of a 
Leyden jar through the inter-atomic or inter- 
molecular ether, i.e. , through the fixed ether within 
different substances, varies with the substance. 
Through free ether the velocity is that of light, or 
185,000 miles a second. 

The velocity of discharge through long con- 
ductors or cables is much lessened by incapacity 
of the cable, and the effects oi induction, and will 
therefore vary in different cases. (See Retard- 
ation.} 

Discharger, Universal —An appa- 
ratus for sending the discharge of a powerful 
Leyden battery or condenser in any desired 
direction. 

The universal discharger consists essentially of 



metallic rods, supported on insulated pillars and 
capable of ready motion, both towards and from 
one another, as well as in vertical and horizon- 
tal p'anes. The object which is to receive the 
discharge is placed on an insulated table between 
the rods, and the latter connected with the 
opposite coatings of the battery or condenser, 
when the discharge passes through it. 

The term universal discharger is sometimes ap- 
plied to the discharging tongs. 

Discharging, Electrically —The 

act of equalizing differences of potential by 
connection with a conductor. 

Discharging Eod. — (See Rod, Discharg- 
ing.) 

Discharging Tongs. — (See Tongs, Dis- 
charging.) 

Disconnect. — To break or open an electric 
circuit. 

Disconnecter. — A key or other device for 
opening or breaking a circuit. 

Disconnecting. — The act of opening or 
breaking an electric circuit. 

Disconnection. — A term employed to des- 
ignate one of the varieties of faults caused 
by the accidental breaking or disconnection 
of a circuit. 

Disconnections of this kind may be : 

(1.) Total; as by a switch inadvertently left 
open; or by the accidental breaking of a part of 
the circuit. 

(2.) Partial ; as by a dirty contact; a loose, or 
badly soldered joint; a poorly clamped binding 
screw; a loose terminal, or a bad earth. 

(3.) Intermittent; as by swinging joints, alter- 
nate expansions or contractions on changes oir 
temperature; the collection of dustand dirt in dry 
weather, and their washing out in wet weather. 

Disconnection, Intermittent — 

Any fault in a line which occurs at intervals 
or intermittently. 

Disconnection, Partial A partial 

fault in a line caused by any imperfect con- 
tact. 



Disconnection, Total 



-A fault in 



a line occasioned by a complete break in the 
circuit. 

Disguised Electricity.— (See Electricity v 
Disguised.) 



J)is.] 



172 



[Dis. 



Disjunctor.— A device employed in a sys- 
tem for the distribution of electric energy by 
means of continuous currents by condensers, 
for the purpose of periodically reversing the 
constant current sent over the line. (See 
Electricity, Distribution of, by Continuous 
Current by Means of Condensers.) 

Dispersion Photometer. — (See Photo?ne- 
ter, Dispersion) 

Displacement Current. — (See Current, 
Displacejnent) 

Displacement, Electric A displace- 
ment of electricity in a uniform and non- 
crystalline dielectric when lines of electro- 
static or magnetic force pass through it. 

The quantity of electricity displaced in any 
homogeneous, non-crystallizable dielectric, 
by the action of an electric force through 
the unit area of cross-section, taken perpen- 
dicular to the direction of the electric force. 

Electric displacement is produced under an 
elastic strain, which continues only while the elec- 
tric force is acting. 

Displacement, Electric, Lines of 

Lines of electric induction along which elec- 
tric displacement takes place. 

Displacement, Electric, Oscillatory 

— A displacement of electricity in a di- 
electric or non-conductor of an oscillatory 
character. 

Displacement, Electric, Theory of 

— A theory which regards the electricity 
produced on an insulated conductor, by in- 
duction through a dielectric, as displaced out 
of the dielectric on to the conductor, or into 
the dielectric from the conductor, by the in- 
fluence of the electric force. 

This conception was introduced into science by 
Maxwell, after a careful study of Faraday's denial 
of action at a distance. 

Suppose a small insulated sphere to receive a 
charge of electricity + Q. It will, by induction, 
produce an equal and opposite charge — Q, on 
the inner surface, .and a similar charge on the 
outer surface of the small hollow sphere, placed 
near it, but separated by the dielectric. There 
has, therefore, been a displacement of electricity 
through the dielectric. The medium of the 



dielectric has connected the two bodies, and the 
phenomena have appeared by the action of the 
electric force on the substance of the dielectric ; 
or, in other words, there has been no action at 
a distance. 

According to this conception, an electric cur- 
rent, called a displacement current, exists in the 
dielectric, while displacement is taking place. 

Displacement Waves.— (See Waves, Dis- 
placement.) 

Disruptive Electric Conduction.— (See 

Conduction, Electric, Disruptive) 

Dissimulated or Latent Electricity. — 

(See Electricity, Dissimulated or Latent) 
Dissipation of Charge. — (See Charge, 

Dissipation of.) 

Dissipation of Energy. — (See Energy, 

Dissipation of.) 

Dissipation of Energy, Hysteresial 

— (See Energy, Hysteresial, Dissipation of. 
Hysteresis) 
Dissipation, Specific Hysteresial 

The specific loss of energy by hysteresis in 
the case of a particular substance. (See 
Hysteresis) 

Dissociate. — To separate a compound sub- 
stance into its constituents. 

Dissociation. — The separation of a chemi- 
cal compound into its constituent parts. 

Dissymmetrical Induction of Armature. 

— (See Armature, Dissymmetrical Induc- 
tion of) 

Dissymmetrical Magnetic Field.— (See 
Field, Magnetic, Dissymmetrical) 

Dissymmetry of Commutation.— (See 
Commutation, Dissymmetry of) 

Distance, Critical, of Lateral Discharge 

Through an Alternative Path The 

distance at which a discharge will take place 
through an air space of given dimensions, in 
preference to passing through a metallic cir- 
cuit of comparatively small resistance. 

Distance, Explosive A term some- 
times employed for sparking distance. (See 
Distance, Sharking) 

Distance, Sparking The distance 



Dis.J 



173 



[Dot. 



at which electrical sparks will pass through 
an intervening air space. (See Spark, Length 
of) 

Distant Station.— (See Station, Distant.) 

Distillation, Destructive — The 

action of heat on an organic substance, 
while out of contact with air, resulting in the 
decomposition of the substance into simpler 
and more stable compounds. 

The different products resulting from destruc- 
tive distillation may be successively collected by 
the ordinary processes of distillation. 

Distillation, Dry A species of de- 
structive distillation. (See Distillation, De- 
structive^) 

Distillation, Electric The dis- 
tillation of a liquid in which the effects of 
heat are aided by an electrification of the 
liquid. 

Beccaria discovered that a liquid evaporates more 
rapidly when electrified than when un electrified. 
Crookes has shown that evaporation is aided 
by negative electrification, or that evaporation 
takes place more rapidly at the negative terminal 
during a discharge than at the positive. (See 
Evaporation, Electric. ) 

Distributing Box of Conduit.— (See Box, 
Distributing, of Conduit.) 

Distributing Station. — (See Station, Dis- 
tributing.) 

Distributing Switch for Electric Light. 

— (See Switch, Distributing, for Electric 
Lights) 
Distribution-Box for Arc Light Circuits. 

— (See Box, Distribution, for Arc Light 
Circuits) 

Distribution, Centre of In a sys- 
tem of multiple-distribution, any place where 
branch cut-outs and switches are located in 
order to control communication therewith. 

The electrical centre of a system of distri- 
bution as regards the conducting network. 

Distribution of Charge.— (See Charge, 
Distribution of) 

Distribution of Electricity.— (See Elec- 
tricity, Distribution of.) 



Distribution of Electricity by Alternat- 
ing Currents (See Electricity, Dis- 
tribution of, by Alternating Currents.) 

Distribution of Electricity by Alternat- 
ing Currents by Means of Condensers. — 
(See Electricity, Distribution of, by Alter- 
nating Currents by Means of Condensers.) 

Distribution of Electricity by Commu- 
tating Transformers. — (See Electricity, 
Distribution of, by Commutating Trans- 
formers) 

Distribution of Electricity by Constant 
Potential Circuit. — (See Electricity, Multi- 
ple Distribution of, by Constant Potential 
Circuit) 

Distribution of Electricity by Contin- 
uous Current by Means of Transformers.— 
(See Electricity, Distribution of, by Conti?i- 
uous Current by Means of Transformers.) 

Distribution of Electricity by Motor- 
Generators. — (See Electricity, Distribution 
of, by Motor-Generators) 

Distribution, Series, of Electricity by 
Constant Current Circuit. — (See Electricity, 
Series Distribution of, by Constant Current 
Circuit) 

District Call-Box.— (See Box, District 
Call) 

Diurnal Inequality of Earth's Magnet- 
ism. — (See Diequality, Diurnal, of Earth's 
Magnetism) 

Divided Magnetic Circuit. — (See Circuit, 
Divided Magnetic) 

Door-Opener, Electric — A device 

for opening a door from a distance by elec- 
tricity. 

Various devices consisting of electro -magnets, 
acting against, or controlling springs or weights, 
are employed for this purpose. 

Dosage, Electro-Therapeutical 

The apportioning of the amount of the cur- 
rent and the duration of its application to the 
body for the treatment of disease. 

Dosage, Galvanic — Electro-thera- 
peutical dosage. (See Dosage, Electro- 
Therapeutical) . 

Dotting Contact. — (See Contact, Dotting) 



Dou.] 



174 



[Dro. 



D o u b 1 e-Break Knife Switch.— (See 

Switch, Double-Break Knifed) 

Double-Carbon Arc Lamp. — (See Lamp, 
Electric Arc, Double-Carbon) 

Double-Cone Insulator. — (See Insulator, 
Double-Cone) 

Double- Connector. — (See Co?inector, 
Double) 

Double-Contact Key.— (See Key, Double- 
Contact) 

Double-Cup Insulator. — (See Insulator, 
Double-Cup) 

Double-Curb. — (See Curb, Double) 

Double-Curb Signaling. — (See Signaling, 
Curb, Double) 

Double-Current Signaling. — (See Signal- 
ing, Double-Curre?it) 

Double-Current Translator.— (See Trans- 
lator, Double-Current) 

D o u b 1 e - C u r r ent Transmitter. — (See 
Transmitter, Double- Current) 

Double-Current Working —The 

employment, in systems of telegraphy, by 
means of suitable keys, of currents from 
voltaic batteries, in alternately opposite 
directions, thus increasing the speed of 
signaling. (See Working, Reverse-Current) 

Double-Fluid Electrical Hypothesis. — 
(See Electricity, Double-Fluid Hypothesis 
of) 

Double-Fluid Voltaic Cell.— (See Cell, 
Voltaic, Double-Fluid) 

Double-Magnet Dynamo-Electric Ma- 
chine. — (See Machine, Dyna?no-Electric, 
Double-Magnet) 

Double-Pen Telegraphic Eegister. — (See 
Register, Double-Pen, Telegraphic) 

D o u b 1 e-Refraction. — (See Refraction, 
Double) 

Double-Refraction, Electric— (See Re- 
fraction, Double, Electric) 

Double-Shackle Insulator. — (See Insula- 
tor, Double-Shackle) 

Double-Shed Insulator. — (See Insulator, 
Double-Shed}, 



Double-Tapper Key. —(See Key, Double- 
Tapper) 
Double-Touch, Magnetization by 

A method for producing magnetization by 
the simultaneous touch of two magnet poles. 
(See Magnetizatioji, Methods of) 

Double-Transmission. — (See Transmis- 
sion, Double) 

Double-Trolley.— (See Trolley, Double) 

Doubler of Electricity. — An early form of 
continuous electrophorus. (See Electro- 
phorus) 

Drifting Torpedo.— (See Torpedo, Drift- 
ing) 

Drill, Electro-Magnetic —A drill 

applied especially to blasting or mining opera- 
tions, operated by means of electricity. 

Drip Loop.— (See Loop, Drip) 

Driven Pulley.— (See Pulley, Driven) 

Driven Shaft— (See Shaft, Driven) 

Driving Pulley. — (See Pulley, Driving) 

Driving Shaft.— (See Shaft, Driving) 

Driving Spider. — (See Spider, Driving) 

Drop, Annunciator — A movable 

signal operated by an electro-magnet, and 
placed on an annunciator, the dropping of 
which indicates the closing or opening of the 
circuit with which the electro-magnet is con- 
nected. 

The falling of the drop may be attended by the 
sounding of a bell or other alarm, or, it may give 
a silent indication. 

Drop, Annunciator, Automatic A 

drop for an annunciator, which on the closing 
of a circuit, falls and holds the circuit closed 
until the drop is raised. 

Drop, Annunciator, Gravity — A 

drop for an annunciator, acted on by gravity 
when released by the movement of the arma- 
ture of an electro-magnet. 

Drop, Automatic — A device for au- 
tomatically closing the circuit of a bell and 
holding it closed until stopped by resetting a 
drop. 



JDro.] 



175 



[Dyn. 




The automatic drop is especially applicable to 
burglar alarms. On the opening of a door or 
shutter, the closing of the circuit moves the 
armature of an elec- 
tro-magnet, and, 
by the falling of a 
drop, closes the cir- 
cuit and holds it 
closed until me- 
chanically opened 
by the replacing of 
the drop. The 
general appearance 
of the automatic 
drop is shown in 
Fig. 215. 

Drop, Calling" 

A n an _ Fig. 215. Automatic Drop. 

nunciator drop employed to indicate to the 
operator in a telegraphic or telephonic system 
that one subscriber wishes to be connected 
with another. 

Drop of Potential. — (See Potential, Drop 
of) 

Drops, Clearing Out —Restoring 

the drops of annunciators to their normal 
position after they have been thrown out of 
the same by the closing of the circuits of their 
magnets. 

These clearing -out devices as placed on most 
forms of annunciators are generaLy mechanical in 
operation. 

Drum Armature. — (See Armature, 
Drum.) 

Drum, Electro-Magnetic A drum, 

used in feats of legerdemain, operated by 
an automatic electro-magnetic make and 
break apparatus. 

Dry Distillation.— (See Distillation, 

Dry) 

Dry Electrode.— (See Electrode, Dry.) 

Dry Pile.— (See Pile, Dry) 

Dry Voltaic Cell.— (See Cell, Voltaic, 
Dry.) 

Dub's Laws.— (See Laws, Dud's.) 
Duplex Cable.— (See Cable, Duplex.) 
Duplex Cut-Out— (See Cut-out, Duplex) 



Duplex Plat Cable.— (See Cable, Flat 
Duplex) 

Duplex Telegraphy. — (See Telegraphy, 
Duplex) 

Duplex Wire. — (See Wire, Duplex) 
Duration of Electric Discharge. — (See 
Discharge, Duration of) 

Duration of Make-Induced Current. — 

(See Curre?it, Make or Break I?iduced, Du- 
ration of) 

Dust Figures, Lichtenberg's — 

(See Figures, Lichtenberg's Dust) 

Dyad. — A chemical element which has two 
bonds by which it can unite or combine with 
another element. 

An element whose atomicity is bivalent. 

Dyeing, Electric The application 

of electricity either to the reduction or the 
oxidation of the salts used in dyeing. 

Goppelsrtfder, in his processes of electric dyeing, 
forms and fixes aniline black on cloth as follows, 
viz.: the cloth, saturated with an aniline salt, is 
placed on an insulated metallic plate, inert to the 
aniline salt, and connected with one pole of a 
battery or other electric source. The other pole 
is connected with a metallic plate on which the 
required design is drawn. On the passage of the 
current, the design is traced in aniline black on 
the cloth. A minute or two suffices for the 
operation. 

A species of electrolytic writing is obtained on 
cloths arranged as above by substituting a carbon 
pencil for the metallic plate. On writing with 
this pencil, as with an ordinary pencil, the pas- 
sage of the current so directed is followed by the 
deposition of aniline black. 

By means of a somewhat similar process writ- 
ing in white on a colored ground is obtained. 

Dynamic Electricity. — (See Electricity, 
Dynamic) 

Dynamics, Electro That branch 

of electric science which treats of the action 
of electric currents on one another and on 
themselves or on magnets. 

The principles of electro dynamics were dis- 
covered by Ampere in 1S21. 

A convenient form of apparatus, for showing 
experimentally the action of one current on 
another, consists of two upright metallic columns 



Djn.] 176 

or pillars, which support horizontal metallic arms 
containing mercury cups, y, and c, Fig. 216. 



[Dyn. 




Fig. 216. Deflection of a Circuit by a Current. 

The circuit is bent in the form of a rectangle, 
circle or solenoid, and terminates in points that 
dip in the mercury cups. The current is led into 
and out of the apparatus at the points -f- and — 
at the base of the upright supports. 

When a magnet, or another circuit, is ap- 
proached to the movable circuit thus provided, 
attractions or repulsions are produced according 
to tro position of the magnet, or the direction of 
the currents in the two circuits. 

If a magnet A B, Fig. 217, be placed, as shown, 




Fig. 211. Deflection of Circuit by a Magnet. 

below the movable circuit C C, the circuit will 
tend to place itself at right angles to the axis of 
the magnet. This movement is the same as 
would occur if electric currents were circulating 
around the magnet in the direction c f the assumed 
Amperian currents. It also illustrates the prin- 
ciple of the electric motor. (See Magnetism, Am- 
pere's Theory of.) 

Ampere has given the results of his investigations 
as to the mutual attractions and repulsions of cur- 



rents in the following statements, which are 
known as Ampere 's Laws: 

(1.) Parallel portions of a circuit attract one 
another if the currents in them are flowing in the: 
same direction, and 
repel one another if ^~7?7/^ 
the currents are flow- *^~~^U(iy 
ng in opposite direc- ^^^ A 

A current flowing ^"^Ull/J 
through a spiral tends 
to shorten the spiral F & 2lS - Action of Solenoid: 

r i.T. t x- - PoIes - 

from the attraction of 

the parallel currents in contiguous turns. 

Similar poles of two solenoids repel each other,, 
as at A, A', Fig. 218, because, when opposed to 
each other, the currents that produce these poles- 





Fig. 2iq. Ampere's Stand. 

are flowing in opposite directions, as may be 
seen from an inspection of the drawing. 

Dissimilar solenoid poles, on the contrary, at- 
tract each other as at A, B, in Fig. 218, since 




Fig. 220. Electro- Dynamic Attraction. 

the currents which produce them flow in the same 
direction. 

In Fig. 219, a form of Ampere's stand is shown T 
in which one of the circuits is in the form of the 



Byn.] 



177 



[Dyn. 




coil M N ; its action on the movable circuit C B, 
is to repel it, since the currents, as shown, are 
flowing in an opposite direction in the adjacent 
portions of the fixed and movable circuits. 

(2.) Two portions of a circuit intersecting each 
other mutually attract each other when the cur- 
rents in both circuits flow 
either towards ox from 
the point of intersection, 
hut repel each other if 
they flow in opposite di- 
rections from this point. 

Thus, in Fig. 220, the 
currents in both circuits 
P Q and A B C D, flow 
-towards and from the 
point of intersection Y, and attract one another 
and cause a motion until the two circuits are 
parallel. 

J£ the currents flow in opposite directions they 
repel each other, and, if free to move, will come 
to rest when parallel to each other ; therefore, 
two portions of a circuit crossing each other tend 
to move until they are parallel, and their currents 
are flowing in the same direction. 

(3.) Successive portions of the circuit of the 
same rectilinear current, that is, a current flowing 
in the same straight line, repel one another. 

A circuit O A, Fig. 221, movable on O, as a 



P Q 

Fig. 221. Continuous 
Rotation 0/ Current. 




Fig. 222. Mutual Action of Magnetic Fields. 

■centre, will be continuously rotated in the direc- 
tion of the curved arrow by the rectilinear cur- 
rent, P Q ; for, the directions of the currents being 
as shown by the arrows, there will be attraction 
in the positions (1) and (2), and repulsion in po- 
sition (4). 

The cause of the mutual attractions and repul- 
sions of electric circuits will readily appear from 
a consideration of the mutual action of their 
magnetic fields. 

Thus an inspection of Fig. 222 shows : 



(i.) That parallel currents flowing in the same 
direction attract, because their lines of force have 
opposite directions in adjoining parts of the cir- 
cuit of these lines. 

(2.) That parallel currents flowing in opposite 
directions repel, because their lines of force have 
the same directions in adjoining parts of the cir- 
cuit. 

These laws may therefore be generalized thus, 
viz.: Lines of magnetic force extending in oppo- 
site directions attract one another; lines of 
magnetic force extending in the same direction 
repel one another. 

Ampere proved that a circuit, doubled on itself 
so that the current flows in opposite directions in 
the two parts, exerts no force on external objects. 
This expedient is adopted in resistance coils to 
prevent any disturbance of the galvanometer 
needles. He also showed that a sinuous circuit, 
or one bent into zigzags, produces the same effects 
of attraction or repulsion as it would if it were 
straight. (See Coil, Resistance.) 

The term sinuous current is sometimes applied 
to the current in a sinuous circuit. (See Current, 
Sinuous.) This must be distinguished from the 
term sinusoidal current, which applies to fluctua- 
tions in the current and not to peculiarities in the 
shape of the conductor. 

When two inclined magnets, free to move, are 
left to their mutual attractions and repulsions, they 
gradually come to rest with their axes parallel to 
each other. 

Two conductors through which electric cur- 
rents are flowing act on one another as two 
magnets would. 

A conductor conveying a current of electricity 
tends to rotate round a magnetic pole. A mag- 
netic pole tends to rotate continuously round an 
electric current. 

The motion of a magnet near a conductor 
produces an electromotive force in that conductor 
provided the conductor cu's the lines of force. 

A magnetized substance becomes magnetized 
when placed in a magnetic field. 

A conductor through which a current of elec- 
tricity is passing tends to wrap itself around a 
neighboring magnetic pole. The following ex- 
periments illustrate this tendency: 

(1.) The experiment suggested by Lodge: A 
powerful current of electricity is passed through 
some eight feet in length of gold thread such as 
is employed for making lace. The thread is 
hung in a vertical position, near a vertical bar 



Dyn.] 



178 



[Dyn. 



magnet. As soon as the current passes, the 
thread will wrap itself around the bar magnet, 
one half of it twisting itself round the north pole, 
the other half round the south pole. 

(2.) The experiment suggested by Professor S. 
P. Thompson: An electric current is sent through 
a stream of mercury while it is flowing between 
two poles of a powerful electro-magnet; when 
the current is sent through the magnet, the 
stream is twisted in spiral directions which vary, 
either with the direction of the current, or with 
the direction of the magnetic polarity. 

(3.) Somewhat similar effects can be shown by 
the rotation of a stream cf gas round a magnetic 
pole placed in an exhausted glass receiver. 

Dynamo. — The name frequently applied to 
a dynamo-electric machine used as a gener- 
ator. (See Machine, Dynamo-Electric) 

Dynamo Balancing 1 Rheostat. — (See 
Rheostat, Dynamo Balancing.) 

Dynamo-Battery. — (See Battery, Dy- 
namo.) 

Dynamo Brush Trimmer. — (See Trim- 
mer, Dynamo Brushy 

Dynamo, Composite-Field — A 

dynamo whose field coils are series and 
separately excited. 

Additional separately excited coils placed on 
the field of a series wound dynamo render it self- 
regulating. 

A composite dynamo is a form of compounded 
dynamo. 

Dynamo, Compound-Wound. — A com- 
pound-wound dynamo-electric machine. (See 
Machine, Dynamo-Electric, Compound- 
Wound^) 

Dynamo, Contact A form of dyna- 
mo in which the space between the arma- 
ture and field magnet poles is so reduced that 
they actually touch one another. 

In contact dynamos both field and armature 
revolve. This form of dynamo has not been very 
successful in practice. 

Dynamo-Electric Machine. — (See Ma- 
chine, Dynamo-Electric?) 

Dynamo-Electric Machine, Alternating 
Current — (See Machine, Dynamo- 
Electric, Alternating Current) 



Dynamo-Electric Machine Armature. — 

(See Armature, Dynaino-Electric Machine) 
Dynamo-Electric Machine Armature 
Coils. — (See Coils, Armature, of Dynamo- 
Electric Machine) 

Dynamo-Electric Machine Armature 
Core. — (See Core, Arinature, of Dyna?no- 
Electric Machine) 

Dynamo-Electric Machine Battery. — 

(See Battery, Dynamo-Electric Machine) 
Dynamo-Electric Machine, Bi-Polar 

— (See Machine, Dynamo-Electric, Bi- 
Polar) 

Dynamo-Electric Machine, Collecting 

Brushes of (See Brushes, Collecting, 

of Dynamo- El ec trie Machine.) 

Dynamo-Electric Machine Commutator 

(See Commutator, Dynamo-Electric 

Machine) 

Dynamo-Electric Machine, Compound- 
Wound — (See Machine, Dynamo- 
Electric, Compound- Wound) 

Dynamo-Electric Machine, Generation of 
Current by (See Current, Genera- 
tion of, by Dynamo-Electric Machine) 

Dynamo-Electric Machine, Field Mag- 
nets (See Magnets, Field, of Dynamo- 
Electric Machine) 

Dynamo-Electric Machine, Methods of 
Increasing the Electromotive Force Gene- 
rated by (See Force, Electromotive, 

Generated by Dynamo-Electric Machine, 
Method of Increasing) 

Dynamo-Electric Machine, Mouse-Mill, 
Sir William Thomson's (See Ma- 
chine, Dyna7no-Electric, Mouse-Mill, Sir 
V/illiam Thomson's) 

Dynamo-Electric Machine, Multipolar 

(See Machine, Dynamo-Electric, 

Multipolar) 

Dynamo-Electric Machine, Pole-Pieces of 

(See Pole-Pieces of Dynamo-Electric 

Machine) 

Dynamo-Electric Machine, Reversibility 

of (See Machine, Dynamo-Electric, 

Reversibility of) 



Dyn.] 



179 



[Dyn. 



Dynamo-Electric Machine, Varieties of 

— (See Machine, Dynamo-Electric, 

Varieties of.) 

Dynamo, Inductor A dynamo- 
electric machine for alternating currents in 
which the differences of potential causing the 
currents are obtained by magnetic changes in 
the cores cf the armature and field coils by 
the movement past them of laminated masses 
of iron inductors. 

The coils corresponding to the armature and 
field magnets of the ordinary dynamo are sta- 
tionary. The laminated masses of iron, employed 
to cause magnetic changes in the cores of the field 
and armature coils, are fixed on an inductor wheel 
which is rapidly revolved in front of them. The 
magnets corresponding to the field magnets are 
called the primary poles, and are magnetized by 
an exciter. The magnets corresponding to the 
armature are called the secondary poles and are 
placed so as to alternate with the primary poles. 
The inductors are so shaped that they carry the 
magnetism of one pole of the primary magnet 
to the secondary poles when the inductor is in 
one position, and of the opposite pole when in a 
slightly different position. The inductor wheel 
therefore acts as a magnetic commutator and 
changes the position of the secondary magnet as 
it rotates, thus producing electromotive force. 
The number of alternations per revolution is 
equal to twice the number of inductors placed on 
the inductor wheel. 

Dynamo, Inverted A dynamo-elec- 
tric machine in which the armature bore or 
chamber is placed below the field magnet 
coils. 

The term inverted is used in contradistinction 
to the overtype dynamo. (See Dynamo, Over- 
type.) 

Dynamo, Mouse Mill A form of 

dynamo-electric machine designed by Sir 
William Thomson to act as the replenisher of 
one of his electrometers. (See Replenisher?) 

Dynamo, Multiphase A polyphase 

dynamo. (See Dynamo, Polyphase. Dyna- 
mo, Rotating Current?) 

Dynamo, Overtype A dynamo- 
electric machine, the armature bore or cham- 
ber of which is placed above the field magnet 
coils instead of below them as in many forms. 



The overtype form of dynamo possesses the 
advantage of better avoiding magnetic leakage. 

Dynamo, Polyphase — A name some- 
times applied to a rotating current dynamo. 
(See Dynamo, Rotating Current.) 

Dynamo, Pyroniagnetic A name 

sometimes applied to a pyromagnetic gen- 
erator. (See Generator, Pyromagnetic?) 

Dynamo, Rotary-Phase A term 

sometimes employed for a rotating current 
dynamo. (See Dynamo, Rotating Current?) 

Dynamo, Separately-Excited A 

separately-excited dynamo-electric machine. 
(See Machine, Dynamo-Electric , Separ- 
ately-Excited?) 

Dynamo, Series A series-wound 

dynamo- electric 
machine. (See Ma- 
chine, Dynamo- 
Electric, Series- 
Wound?) 

Dynamo, Shunt 

— A shunt- 
wound dynamo- 
electric machine. 
(See Machine, 
Dynamo - Electric, 
Shunt- Wound?) 

Dynamograph. 

— A term some- 
times applied to a 
type-writing tele- 
graph that records 
the message in 
type-written char- 
acters, both at the 
sending and the 
receiving ends. 

Dynamometer. 
— A name given to ' I 
a variety of appar- p{ gt 
atus for measuring 
the power of an engine or motor. 

In all dynamometers the strain on the belt or 
other moving part is measured, say in pounds, 
and the speed of the moving part is also measured 
in feet per second. The product of the strain in 




2 2 S' Parsons' Dyna- 
mometer. 



Dyn.] 



180 



[Dyn. 



pounds by the velocity in feet per second, di- 
vided by 550, will give the horse power. 

One of the many forms of dynamometers is 
shown in Fig. 223. It is known as Parsons' Dy- 
namometer. 

The driving pulley is shown at A, and the 
driven pulley at C. Weights hung at Q x , are va- 
ried so as to maintain the axes of the suspended 
pulleys, D and B, as nearly as possible at the 
same height. Then the tension T x and T 2 , on 
the sides O and O', of the belts, will be repre- 
sented by the following equation : 

1 2 - 1, _, 

from which, knowing the belt speed, the horse 
power may be deduced. 

There are several other forms of dynamometer, 
such as the cradle dynamometer, in which the 
machine is supported on knife edges and the 
torque or pull exerted on or by the machine is 
balanced by weights sliding on a lever. In these 
dynamometers the power is transmitted through 
them and they are therefore called transmission 
dynamometers. 

Dynamometer, Electro A form of 

galvanometer for the measurement of electric 
currents. 

In Siemens' Electro-Dynamometer, shown in 
Fig. 224, there are two coils ; a fixed coil, C, se- 
cured to an upright support, and a movable coil, 
L, consisting often of but a single turn of wire. 
The movable coil is suspended by means of a 
thread and a delicate spring, S, capable of being 
twisted by turning a milled screw-head through 
an angle of torsion measured on a scale by means 
of an index connected to the screw-head. The 
two ends of the movable coil dip into mercury 
cups so connected that the current to be measured 
passes through the fixed and movable coils in 
series. 

When ready for use the movable coil is at right 
angles to the fixed coil. The current to be meas- 
ured is then sent into the coils, and their mutual 
action tends to place the movable coil parallel to 
the fixed coil against the torsion of the spring, S. 
The amount of this force can be ascertained by 
determining the amount of torsion required to 
bring the movable coil back to its zero position. 



Since the same current passes through both the 
fixed and movable coils, and they both act on 
each other, the deflecting force here is evidently 
proportional to the square of the strength of the 




Fig. 224. Siemens' Elect ro- 



current to be measured. The deflecting force, 
and consequently the current strength, is there- 
fore proportional to the square root of the angle 
of torsion, and not directly to the angle of tor- 
sion. 

Dyne. — The unit of force. 

The force which in one second can impart 
a velocity of 1 centimetre per second to a 
mass of 1 gramme. 

The dyne is the unit of force, or a force capa- 
ble, after acting for one second on a mass of I 
gramme, of giving it a velocity of I centimetre 
per second. The weight of a body in dynes, or the 
force with which it gravitates, is equal to its 
mass in grammes, multiplied by the acceleration 
imparted to it in centimetres per second. For 
this latitude the acceleration is about 981 centi- 
metres per second. 



u.] 



181 



[Edd, 



E. — A contraction sometimes used for 
earth. 

A contraction sometimes used for electro- 
motive force, or E. M. F., as in the well- 
known formula for Ohm's law, 

R 

E. M. D. P.— A contraction for electro- 
motive difference of potential. (See Poten- 
tial, Difference of, Electromotive I) 

E. M. F. — A contraction generally used for 
electromotive force. (See Force, Electro- 
motive?) 

Earth. — A fault in a telegraphic or other 
line, caused by accidental contact of the line 
with the ground or earth, or with some con- 
ductor connected with the latter. 

This is more frequently called a ground. 

Earths are of three kinds, viz.: 

(I.) Dead or Total Earth. 

(2.) Partial Earth. 

(3.) Intermittent Earth. 

The term earth is also applied to a plate buried 
in the ground, and intended to make a good con- 
tact between the earth and a wire circuit, which 
is connected with the plate. 

Earth Circuit.— (See Circuit, Earthy 

Earth-Circuited Conductor. — (See Con- 
ductor, Earth-Circuited I) 

Earth Currents. — Electric currents flow- 
ing through different parts of the earth caused 
by a difference of potential at different points. 

The causes of these differences of potential are 
various and are not well understood. 

Earth, Dead or Total A fault in 

a telegraphic or other line in which the line 
is thoroughly grounded or connected with 
the earth. 

Dead earth is sometimes called total earth. 

Earth-Grounded Wire. — (S e e Wire, 
Ea rth- Groimded. ) 

Earth, Intermittent —A swinging 

earth. (See Earth, Swinging or Intermit- 
tent?) 

Earth or Ground. — That part of the earth 



or ground which forms part of an electric 
circuit. 

A circuit is put to earth or ground when the 
earth is used for a portion of the circuit. 

The resistance of an earth connection may vary 
in time from the following causes, viz.: 

(I. ) The corrosion of the ground plate. This is 
especially apt to occur in the case of a copper 
plate. 

(2.) From polarizaiion, a counter- electro- 
motive force being produced, thus introducing a 
spurious resistance into the circuit. (See Resist- 
ance, Spurious.) 

Earth, Partial A fault in a tele- 
graphic or other line in which the line is in 
partial connection with the earth. 

The term partial earth is used in contradistinc- 
tion to dead or total earth. 

Earth, Return A circuit in which 

the return current passes back to the source 
through the earth. 

Earth, Swinging or Intermittent ■ 

— A fault in a telegraphic or other line in 
which the action of the wind, or occasional 
expansion by heat, brings the line into inter- 
mittent contact with the earth. 

Earth, Total A term sometimes 

used for dead earth. (See Earth, Dead or 
Total.) 

Ebonite. — A tough, hard, black substance, 
composed of india rubber and sulphur, which 
possesses high powers of insulation and of 
specific inductive capacity. 

Ebonite is often called vulcanite. 

Vulcanite rubbed with cat-skin acts as one of 
the best known substances for becoming electri- 
fied by friction. For this purpose both substances 
should be thoroughly dried. 

Economic Co-efficient of Dynamo-Elec- 
tric Machine — (See Co-efficient, Econo?nic, 
of a Dyjiamo-Electric Machine?) 

Eddy Currents. — (See Currents, Eddy.) 

Eddy Currents, Deep-Seated (See 

Currents, Eddy, Deep-Seated?) 

Eddy Currents, Superficial -(See 

Currents, Eddy, Superficial?) 



Edd.] 



182 



[EfL 




Fig. 223. Electric 
Eeh 



Eddy-Displacement Currents.— (See Cur- 
rents, Eddy-Displacement^) 

Eel, Electric —An eel possessing 

the power of giving powerful electric shocks. 

The gymnotus electricus. 

The electricity is produced by an organ ex- 
tending the entire length of 
the body. 

According to Faraday, the 
shock given by a specimen 
of the animal examined by 
him was equal to that of 15 
Leyden jars, having a total 
surface of 25 square feet. 
Fig. 225 shows the general 
appearance of the animal. 

Effect, Acheson 

The increase in the electro- 
motive force of the sec- 
ondary of a transformer by 
the action of the changes 
in temperature of its core. 
(See Electricity, Cal.) 

Effect, Chemical 

— The effect occasioned by atomic combina- 
tion, which results in a loss of those properties 
or peculiarities by which the substances en- 
tering into combination are ordinarily recog- 
nized. 

Atomic combination, resulting in the for- 
mation of new moleculeSc 

The formation of new molecules necessitates the 
possession by the new substance of properties dis- 
tinct and separate from those of its constituents. 

Black carbon, and yellow sulphur, for example, 
both solids, unite chemically to form a trans- 
parent colorless liquid. 

Chemical changes differ from physical changes, 
which latter can occur in a substance without the 
formation of new molecules, and consequently 
without the loss by it of the properties it ordi- 
narily possesses. 

Thus a sheet of vulcanite, electrified by friction, 
still retains its characteristic density, shape, color, 
etc. 

Effect, Counter-Inductive — — — The 

opposal of current or charge by means of a 
counter-electromotive force produced by in- 
duction. 



In the Thomson counter-electromotive force 
lightning arrester, a counter- electromotive force, 
produced by the inductive effects of the passage 
of the bolt to earth, protects the instrument by 
opposing the passage of the bolt. (See Arrester^ 
Lightning, Counter-Electromotive Force.) 

Effect, Edison An electric dis- 
charge which occurs between one of the ter- 
minals of the incandescent filament of an 
electric lamp, and a metallic plate placed near 
the filament but disconnected therefrom, as 
soon as a certain difference of potential is 
reached between the lamp terminals. 

The effect of the discharge is to produce a cur- 
rent in a circuit connected to one pole of the lamp 
terminals and the metallic plate, as may be shown 
by means of a galvanometer. 

Effect, Electrotonic —An altered 

condition of excitability of a nerve produced 
when in the electrotonic state. (See Elec~ 
trotonusl) 

Effect, Faraday -The rotation of 

the plane of polarization of a beam of plane 
polarized light by its passage through a 
magnetic field. 

Lodge suggests the following explanation for 
the Faraday effect: As is well known, a strongly 
magnetized medium possesses a different magnetic 
susceptibility to additional magnetizing forces in 
the same direction than it does in the opposite 
direction. It therefore follows that the vibra- 
tions are resolved into two opposed circular com- 
ponents, which travel through the medium with 
different rates of velocity, since one tends to mag- 
netize it and the other to demagnetize it. The 
plane of rotation will therefore be rotated. 

He also suggests the following explanation for 
the Faraday effect, viz.: He assumes that the 
Amperian molecular currents in such substances 
as exhibit rotation in a magnetic field, do not 
consist of two equal «nd opposite electrical cur- 
rents, but that osas of the currents is slightly 
stronger than the other. Suppose, for example- 
that in iron the positive Amperian current is 
weaker than the negative, and that the ether as 
a whole is rotating with the negative current. 
Any ethereal vibration entering such a medium 
will begin to screw itself in the direction opposed 
to that of the magnetizing current. In copper, 
or other similar substances, the rotation should 
take place in the opposite direction. 



Eff.J 



183 



[Eff. 



Effect, Ferranti 



-An increase in the 



electromotive force, or difference of potential, 
of mains or conductors towards the end of the 
same farthest from the terminals that are con- 
nected with a source of constant potential. 

The Ferranti effect refers to the increase of the 
electromotive force on the mains employed in 
systems for the transmission of electrical energy 
by means of alternating currents. It was found, 
for example, in the currents used on the 
mains connected with one of Mr. Ferranti's alter- 
nating dynamos and leading to the town of Dept- 
ford, that instead of finding a drop of potential at 
the ends of the mains farthest from the dynamo, 
as was expected, a notable increase in the poten- 
tial occurred. These effects were observed dur- 
ing the laying of the mains. Testing the poten- 
tial by placing an incandescent lamp in the circuit 
across the mains, the increase of the potential 
with the increase of the length of the main was 
shown by the increased brilliancy of the light of 
the incandescent lamp. 

Various explanations have been given as the 
cause of the Ferranti effect. 

Effect, Hall A transverse elec- 
tromotive force, produced by a magnetic 
field in substances undergoing electric dis- 
placement. 

This transverse electromotive force is probably 




Fig. 226. Hall Effect. 
due to magnetic whirls, in a manner similar to 
the Faraday effect. 

The Hall effect is produced by placing a very 
thin metallic strip, conveying an electric current, 
in a strong magnetic field. 

The cross A B C D, Fig. 226, is cut out of a 



gold leaf or other very thin metallic sheet. The 
ends A and B, are connected with the terminals 
of a battery S, and the ends C and D, with the 
galvanometer G. 

None of the battery current can therefore flow 
through the galvanometer. 

If, now, the metallic cross be placed in a power- 
ful magnetic field, the lines of force of which are 
perpendicular to the plane of the cross, the deflec- 
tion of the galvanometer needle will show the 
existence of a current, which, if the battery cur- 
rent flows in the direction of the arrow, or from A, 
to B, and the lines of magnetic force pass through 
the paper from the front to the back of the sheet, 
when the cross is formed of gold, silver, platinum 
or tin-foil, will flow through C D, from C to D, 
but in the opposite direction if formed of iron. 
These effects cease if the conductor is increased 
in thickness beyond a certain extent. 

As regards the production of the Hall effect by 
the influence of a magnetic field on conductors, 
Mr. Shelford Bidwell suggests that since magnet- 
ism affects the conductivity of metals in a 
complicated manner, it is possible that metallic 
substances conveying an electric current in a 
magnetic field are more or less strained by the 
mechanical forces, and that, therefore, heat may 
be unequally developed, and that the resistance 
thus being modified in places, there may be pro- 
duced disturbances of the flow which may 
rapidly produce in part a transverse electromotive 
force. 

Effect, Hall, Real A transverse elec- 
tromotive force produced in conductors con- 
veying electric currents, by magnetic whirls, 
in a manner similar to that in which the Far- 
aday effect is produced. (See Effect, Fara- 
day.) 

Effect, Hall, Spurious An appa- 
rent transverse electromotive force produced 
in conductors conveying electric currents in 
magnetic fields, by changes, produced by mag- 
netism, in the conductivity of the metals, and 
the consequent production of local distur- 
bances in the electrical flow, thus resulting 
in an apparent transverse electromotive force. 

Effect, Impulsion The restoration 

or loss of sensitiveness of a photo-voltaic cell 
to the action of light, produced by means of 
an impulse such as that of a tap or blow, or 
electro-magnetic impulse. 



Eff.] 



184 



[Eff. 



Effect, Joule The heating effect 

produced by the passage of an electric cur- 
rent through a conductor, arising merely from 
the resistance of the conductor. 

The rate at which this occurs is proportional to 
the resistance of the conductor through which 
the current is passing multiplied by the square 
of the current. (S. j e Heat, Electric.) 

Effect, Kerr A term applied to 

the electrostatic optical effect discovered by 
Dr. Kerr, viz., that a beam of plane polarized 
light is elliptically polarized when transmitted 
across an electrostatic field. 

The Kerr effect does not take place in free space, 
but occurs in different senses or directions in dif- 
ferent media. 

Like the Faraday effect, the Kerr effect de- 
pends on the presence of a dense medium, and the 
direction of the effect depends on the character of 
the medium. 

Effect, Mordey — A term some- 
times applied to a decrease in the value of 
hysteresis in the iron of a dynamo armature at 
full load. 

Effect, Peltier The heating ef- 
fect produced by the passage of an electric 
current across a thermo-electric junction or 
surface of contact between two different met- 
als. (See Junction, Thermo-Electric.) 

The passage of the current across a thermo- 
electric junction produces either heat or cold. If 
heat is produced by its passage in one direction, 
cold is produced by its passage in the opposite 
direction. The Peltier effect may, therefore, 
mask the Joule effect. 

The Peltier effect is the converse of the thermo- 
electric effect, where the unequal heating of metal- 
lic junctions results in an electric current. (See 
Effect, Joule. Effect, Thomson.) 

The quantity of heat absorbed or em'tted by 
the Peltier effect is proportional to the current 
strength, and not, as in the Joule effect, to the 
square of the current. 

Effect, Photo-Yoltaic The change 

in the resistance of selenium or other 
substances effected by their exposure to 
light. The photo-voltaic effect is seen in 
the case of the selenium cell. (See Cell, 
Selenium?) 



Effect, Seebeck A term sometimes 

used instead of thermo-electric effect. (See 
Effect, Thermo-Electric?) 

This term has nearly passed out of use. 

Effect, Skin The tendency of alter- 
nating currents to avoid the central portions 
of solid conductors and to flow or pass mostly 
through the superficial portions. 

The so-called skin effect is more pronounced 
the more frequent the alternations. 

Effect, Thermo-Electric The pro- 
duction of an electromotive force at a 
thermo-electric junction by a difference of 
temperature between that junction and the 
other junction of the thermo-electric couple. 
(See Couple, Thermo-Electric. Junction, 
Thermo-Electric.} 

Effect, Thomson The production of 

an electromotive force in unequally heated 
homogeneous conducting substances. 

A term also applied to the increase or de- 
crease in the differences of temperature in an 
unequally heated conductor, produced by the 
passage of an electrical current through the 
conductor. 

The Thomson effects vary according to whether 
the current passes irom a colder to a I otter part 
of the conductor, or the reverse. 

The Thomson effects differ in direction in differ- 
ent metals, and are absent in lead. Thomson has • 
pointed out the similarity between this species of 
thermo-electric phenomena, and convection by 
heat, or the phenomena of a liquid circulating in 
a closed rectangular tube, under the influence of 
differences of temperature, in which the heated 
fluid gives out heat in the cooler parts of the cir- 
cuit, and takes in heat in the warmer parts. 
This would presuppose that positive electricity 
carries heat in copper like a real fluid, but that 
in iron it acts as though its specific heat were a 
negative quantity, in which respect it is unlike a 
true fluid. 

" We may express," says Maxwell, " both the 
Peltier and the Thomson effects by stating that 
when an electric current is flowing from places of 
smaller 1o places of greater thermo-electric power, 
heat is absorbed, and when it is flowing in the 
reverse direction heat is generated, and this 
whether the difference of thermo-electric power 
in the two places arises from a difference in the 



Eff.] 



185 



[Ele. 



nature of the metals, or from a difference of tem- 
perature in the same metal." 

Effect, Yoltaic A difference of 

potential observed -at the point of contact of 
two dissimilar metals. 

This difference of potential was formerly as- 
cribed to the mere contact of dissimilar metals, 
and is even yet believed by some to be due to 
such contact. It is, however, perhaps more ac- 
curately ascribed to the greater affinity of oxygen 
of the air for the positive metal than for the 
negative metal; that is, to a chemical action on 
the positive element of a voltaic couple. 

Effective Electromotive Force.— (See 
Force, Electromotive, Effectived) 

Effective Secondary Electromotive 
Force. — (See Force, Electromotive, Second- 
ary, Effective^ 

Effects of Capillarity on Yoltaic Cells. — 
(See Capillarity, Effects of, on Voltaic Cell?) 

Efficiency, Commercial The useful 

or available energy produced divided by the 
total energy absorbed by any machine or ap- 
paratus. 

The Commercial Efficiency = 
W ___ W 

M W-fwf m, 
when W = the useful or available energy; M = 
the total energy; w, the energy absorbed by the 
machine, and m, the stray power, or power lost 
in friction of bearings, etc., air friction, eddy cur- 
rents, etc. 

Efficiency, Commercial, of Dynamo 

— The useful or available electrical energy in 
the external circuit, divided by the total 
mechanical energy required to drive the 
dynamo that produced it. (See Co-efficient, 
Economic, of a Dynamo-Electric Machine?) 

Efficiency, Electric The useful or 

available electrical energy of any source, 
divided by the total electrical energy. 

W 

The electric efficiency == . _, where W, 

W -\- w 

equals the useful or available electrical energy, 
and w, the electrical energy absorbed by the 
machine. 

Efficiency of Conversion.— The ratio be- 
tween the energy present in any result and 
the energy expended in producing that result. 



Efficiency of Conversion of Dynamo. — 

(See Conversion, Efficiency of, of Dynamo?) 
Efficiency of Transformer. — (See Trans- 
former, Efficiency of) 

Efficiency, Quantity, of Storage Battery 

The ratio of the number of ampere- 
hours taken out of a storage or secondary 
battery, to the number of ampere-hours put in 
the battery in charging it. 

Efficiency, Real, of Storage Battery 

— The ratio of the number of watt-hours 
taken out of a storage battery, to the number 
of watt-hours put into the battery in charg- 
ing it. 

Efflorescence. — The drying of crystals by 
losing their water of crystallization and be- 
coming pulverulent or crumbling. 

The term is sometimes loosely applied to 
the deposition of solid matter by the crystal- 
lization of a salt, above the line of the liquid, 
on the surface of a vessel containing a vaporiz- 
able saline solution. 

The liquid, by capillarity in a porous vessel, or 
by adhesion to the walls of an impervious vessel, 
rises above the level of the main liquid line, and, 
evaporating, deposits crystals on the vessel. 

This process is technically called creeping, and 
is often the cause of much annoyance in voltaic 
cells. 

Egg, Philosopher's A name given 

to the ovoidal, or egg-shaped mass of light 
that appears when a convective discharge is 
taken between two electrodes in a partial 
vacuum. 

The philosopher's egg is but one of the shapes 
assumed by the convective discharge. (See Dis- 
charge, Convective. ) 

Elasticity, Electric The quotient 

arising from dividing the electric stress by 
the electric strain. 

It can be shown mathematically that the elec- 
tric elasticity is equal to 4, or 4 x 3. 14 16, divided 
by the specific inductive capacity. 

Electrepeter. — An instrument for chang- 
ing the direction of an electric current. 

The old term for switch, key, or pole changer. 
(Obsolete.) 

Electric. — Pertaining to electricity. 



Ele.] 



186 



[Ele. 



Electric Absorption. — (See Absorption, 
Electric?) 

Electric Acoutemeter. — (See Acouteme- 
ter, Electric?) 

Electric Actinometer. — (See Actinomecer, 
Electric.) 

Electric Adhesion. — (See Adhesion, Elec- 
tric.) 

Electric Aging of Alcohol. — (See Alco- 
hol, Electric Aging of.) 

Electric Alarm. — (See Alarm, Electric.) 

Electric Alarm Speaking-Tube Mouth- 
piece. — (See Speaking-Tube Mouth-Piece, 
Electric Alarm?) 

Electric Amalgam. — (See Amalgam, 
Electric?) 

Electric Ammunition Hoist. — (See Hoist, 
Ammunition, Electric?) 

Electric Analysis. — (See Analysis, Elec- 
tric?) 

Electric Analyzer. — (See Analyzer, Elec- 
tric?) 

Electric Anemometer. — (See Ane?nome- 
ter, Electric?) 

Electric Annealing. — (See Annealing, 
Electric?) 

Electric Annunciator Clock. — (See 
Clock, Electric Annunciator?) 

Electric Arc. — (See Arc, Electric?) 

Electric Arc Blow-Pipe. — (See Blow- 

? Pipe, Electric Arc.) 

\ 

' Electric Argand Burner, Hand-Lighter 

(See Burner, Argand Electric ; Hand- 

Eighter?) 

Electric Argand Burner, Plain-Pendant 

■ — (See Burner, Argand Electric, 

Plain-Pendant?) 

Electric Argand Burner, Ratchet-Pend- 
ant (See Burner, Argand Electric, 

Ratchet-Pendant?) 

Electric Balance. — (See Balance, Elec- 
tric?) 

Electric Balloon. — (See Balloon, Elec- 
tric?) 

Electric Battery. — (See Battery, Elec- 
tric?) 



Electric Bell, Continuous-Sounding 

— (See Bell, Continuous-Sounding Electric?) 
Electric Bell, Differential.— (See Bell, 

Differential Electric?) 

Electric Bell, Mechanical.— (See Bell, 

Electro-Mechanical?) 

Electric Bell Pull.— (See Pull, Bell, Elec- 
tric) 

Electric Bioscopy. — (See Bioscopy, Elec- 
tric?) 

Electric Bi-Polar Bath.— (See Bath, Bi- 
polar?) 

Electric Blasting. — (See Blasting, Elec- 
tric?) 

Electric Bleaching.— (See Bleaching, 
Electric?) 

Electric Blow-Pipe. — (See Blow-Pipe, 
Electric?) 

Electric Boat. — (See Boat, Electric?) 
Electric Bobbin. — (See Bobbin, Electric?) 
Electric Body-Protector.— (See Body -Pro- 
tector, Electric?) 

Electric Boiler-Feed. — (See Boiler-Feed, 
Electric?) 

Electric Branding. — (See Branding, Elec- 
tric?) 

Electric Breeze. — (See Breeze, Electric?) 
Electric Bridge. — (See Bridge, Electric?) 
Electric Buoy. — (See Buoy, Electric?) 
Electric Burner. — (See Burner, Auto- 
matic Electric) 

Electric Buzzer. — (See Buzzer, Electric.) 
Electric Cable. — (See Cable, Electric) 
Electric Calamine. — (See Calamine, Elec- 
tric?) 
Electric Call-Bell.— (See Bell, fall) 
Electric Calorimeter. — (See Calorimeter, 
Electric) 

Electric Candle. — (See Candle, Electric) 
Electric Case-Hardening.— (See Case- 
Hardening, Electric) 

Electric Cauterization. — (See Cauteriza- 
tion, Electric) 

Electric Cauterizer. — (See Cauterizer, 
Electric) 



Me.] 



187 



[Ele. 



Electric Cautery. — (See Cautery, Elec- 
tric) 

Electric Charge — (See Charge, Electric) 
Electric Chimes. — (See Chimes, Electric) 

Electric Chronograph. — (See Chrono- 
graph, Electric) 

Electric Chronoscope. — (See Chronoscope, 
Electric) 

Electric Cigar-Lighter. — (See Lighter, 
Cigar, Electric) 

Electric Circuit. — (See Circuit, Electric) 

Electric Cleats. — (See Cleats, Electric) 

Electric Clepsydra. — (See Clepsydra, Elec- 
tric) 

Electric Clock.— (See Clock, Electric) 
Electric Coil.- (See Coil, Electric) 
Electric Column. — (See Column, Elec- 
tric.) 

Electric Communicator. — (See Commu- 
nicator, Electric) 

Electric Conducting. — (See Conducting, 
Electrical) 

Electric Conduction.— (See Conduction, 
Electric) 

Electric Convection of Heat.— (See Heat, 
Electric Convection of) 

Electric Cord.— (See Cord, Electric) 

Electric Counter. — (See Counter, Elec- 
tric) 

Electric Creeping. — (See Creeping, Elec- 
tric) 

Electric Cross. — (See Cross, Electric) 

Electric Crucible. — (See Crucible, Elec- 
tric) 

Electric Current. — (See Current, Elec- 
tric) 

Electric Cystoscopy. — (See Cystoscopy^ 
Electric) 

Electric Damping. — (See Damping, Elec- 
tric) 

Electric Death. — (See Death, Electric) 

Electric Decomposition.— (See Decom- 
position, Electric) 



Electric Density. — (See Density, Elec- 
tric) 

Electric Deposition. — (See Deposition, 
Electric) 

Electric Determination of Longitude. — 
(See Lo7igitude, Electric Determination 
of) 

Electric Displacement. — (See Displace- 
ment, Electric) 

Electric Distillation. — (See Distillation, 
Electric) 

Electric Door-Bell Pull.— (See Pull, 
Electric Door-Bell) 

Electric Double-Refraction. — (See 
Double-Refraction, Electric) 

Electric Dyeing. — (See Dyeing, Electric) 

Electric Dynamometer, Siemens'. — (See 
Dynamometer, Electro) 

Electric Eel. — (See Eel, Electric) 

Electric Efficiency. — (See Efficiency, Elec- 
tric) 

Electric Elasticity. — (See Elasticity, Elec- 
tric) 

Electric Elevator. — (See Elevator, Elec- 
tric) 

Electric Endosmose. — (See Endosmose, 
Electric.) 

Electric Energy. — (See Energy, Electric) 

Electric Entropy. — (See Entropy, Elec- 
tric) 

Electric Escape. — (See Escape, Electric) 

Electric Etching. — (See Etching, Elec- 
tro) 

Electric Evaporation. — (See Evapora- 
tion, Electric) 

Electric Excitability of Nerve or Mus- 
cular Fibre. — (See Excitability, Electric, 
of Nerve or Muscular Fibre) 

Electric Exhaustion. — (See Exhaustion, 
Electric) 

Electric Expansion. — (See Expansion, 
Electric) 

Electric Exploder. — (See Exploder, Elec- 
tric Mine) 



EleJ 



188 



[Ele. 



Electric Explorer. — (See Explorer, Elec- 
tric^ 

Electric Field. — (See Field, Electric?) 

Electric Figures, Breath — (See 

Figures, Electric, Breath?) 

Electric Figures, Lichtenberg's 

(See Figures, Electric, Lichtenberg's?) 
Electric Fishes. — (See Fishes, Electric?) 
Electric Fly.— (See Fly, Electric?) 
Electric Flyer. — (See Flyer, Electric?) 
Electric Fog. — (See Fog, Electric?) 
Electric Force. — (See Force, Electric?) 
Electric Furnace. — (See Furnace, Elec- 
tric?) 
Electric Fuse. — (See Fuse, Electric?) 
Electric Gas-Lighting. — (See Gas-Light- 
ing, Electric?) 

Electric Gas-Lighting, Multiple 

(See Gas-Lighting, Multiple Electric?) 

Electric Gas-Lighting Torch. — (See 
Torch, Electric Gas-Lighting?) 

Electric Gastroscope. — (See Gastroscope, 
Electric?) 

Electric Gilding. — (See Gilding, Electric?) 
Electric Governor. — (See Governor, Elec- 
tric?) 

Electric Hand-Lighter for Argand 
Burner. — (See Burner, Argand Electric 
Hand-Lighter?) 

Electric Head-Bath.— (See Bath, Head, 
Electric?) 

Electric Head-Light. — (See Head-Light, 
Locomotive, Electric?) 

Electric Heat. — (See Heat, Electric?) 
Electric Heater. — (See Heater, Electric?) 
Electric Horse Power. — (See Power, 
Horse, Electric?) 

Electric Hydrotasimeter. — (See Hydro- 
tasimeter, Electric?) 

Electric Ignition. — (See Ignition, Elec- 
tric?) 

Electric Images. — (See Images, Electric?) 

Electric Incandescence. — (See Incandes- 
cence, Electric?) 



Electric Indicator for Steamships. — (See 

Indicator, Electric, for Steamships.) 

Electric Indicators. — (See Indicators* 
Electric.) 

Electric Inertia. — (See Inertia, Electric.) 

Electric Insolation. — (See Insolation, 
Electric.) 

Electric Installation. — (See Installation, 
Electric.) 

Electric Insulation. — (See Insulation, 
Electric?) 

Electric Irritability. — (See Irritability, 
Electric?) 

Electric Jar. — (See Jar, Electric?) 

Electric Jewelry. — (See Jewelry, Elec- 
tric?) 

Electric Lamp, Arc (See Lamp, 

Electric. Arc.) 

Electric Lamp-Bracket. — (See Bracket, 
Lamp, Electric?) 

Electric Lamp, Incandescent (See 

Lainp, Electric, Incandesce?it?) 

Electric Lamp, Semi-Incandescent 

— (See Lamp, Electric, Semi-Incandescent .) 

Electric Lamp, Socket for. — (See Socket, 
Electric Lamp?) 

Electric Launch. — (See Launch, Elec- 
tric?) 

Electric Letter-Box. — (See Letter-Box, 
Electric?) 

Electric Light. — (See Light, Electric?) 

Electric Lighting, Central Station 

— (See Station, Central?) 

Electric Lighting, Isolated (See 

Lighting, Electric, Isolated?) 

Electric Light or Power Cable. — (See 
Cable, Electric Light or Power?) 

Electric Lock. — (See Lock, Electric?) 

Electric Locomotive. — (See Locomotive,. 
Electric?) 

Electric Log. — (See Log, Electric?) 

Electric Loom. — (See Loom, Electric?) 

Electric Loop. — {See Loop, Electric?) 

Electric Machine, Frictional (See 

Machine, Frictional Electric?) 



lie.] 



189 



LElc. 



Electric Main.— (See Main, Electric?) 
Electric Masses.— (See Masses, Electric) 
Electric Measurements. — (See Measure- 
ments, Electric?) 

Electric Megaloscope. — (See Megalo- 
scope, Electric?) 
Electric Meter. — (See Meter, Electric?} 
Electric Mine-Exploder.— (See Mine-Ex- 
ploder, Electro-Magnetic. Fuse, Electric?) 

Electric Motor. — (See Motor, Electric?) 

Electric Motor, High-Speed (See 

Motor, Electric, High-Speed) 

Electric Motor, Low-Speed (See 

Motor, Electric, Low-Speed?) 

Electric Multipolar Bath (See 

Bath, Multipolar, Electric?) 

Electric Musket. — (See Musket, Electric?) 
Electric Organ. — (See Organ, Electric?) 
Electric Oscillations. — (See Oscillations, 
Electric?) 

Electric Osmose. — (See Osmose, Electric?) 
Electric Osteotome. — (See Osteototne, 
Electric?) 

Electric Overtones.— (See Overtones, 
Electric) 

Electric Pen. — (See Pen, Electric?) 
Electric Pendant. — (See Pendant, Elec- 
tric?) 

Electric Pendant-Lamps. — (See La??ips, 
Electric Pendant?) 

Electric Pendulum. — (See Pendulum, 
Electric?) 

Electric Permeancy. — (See Permeancy, 
Electric?) 

Electric Phosphorescence. — (See Phos- 
phorescence, Electric?) 

Electric Photometer.— (See Photometer?) 
Electric Piano. — (See Piano, Electric.) 
Electric Plow. — (See Plow, Electric.) 
Electric Position-Finder. — (See Finder, 
Position, Electric?) 

Electric Potential. — (See Potential, Elec- 
tric?) 



Electric Power. — (See Power, Electric.) 
Electric Probe. — (See Probe, Electric?) 
Electric Prostration. — (See Prostration, 

Electric?) 
Electric Protection. — (See Protection, 

Electric, of Houses, Ships and Buildings?) 
Electric Protection of Metals. — (See 

Metals., Electrical Protection of.) 

Electric Pulse. — (See Pulse, Electrical?! 

Electric Pyrometer, Siemens'. — (See 
Pyrometer, Siemens ', Electric.) 

Electric Radiometer, Crookes' 

(See Radiometer, Electric, Crookes'.) 

Electric Range-Finder. — (See Finder, 
Range, Electric.) 

Electric Ratchet-Pendant for Argand 
Burner. — (See Burner, Argand Electric, 
Ratchet-P enda7it . ) 

Electric Ray. — (See Ray, Electric?) 

Electric Reaction Wheel. — (See Wheel, 
Reaction, Electric?) 
Electric Rectification of Alcohol. — (See 

Alcohol, Electric Rectification of.) 

Electric Refining of Metals. — (See Metals, 
Electric Refining of.) 

Electric Register, Watchman's 

(See Register, Watchman's Electric.) 

Electric Registering Apparatus. — (See 
Apparatus, Registering, Electric?) 

Electric Relay-Bell.— (See Bell. Relay, 
Electric.) 

Electric Repulsion. — (See Repulsion, 
Electric.) 

Electric Resistance. — (See Resistance, 
Electric?) 

Electric Resonance. — (See Resonance, 
Electric.) 

Electric Retardation.— (See Retardation, 
Electric.) 

Electric Rings. — (See Rings, Electric?) 

Electric Safety Lamps. — (See La?np, 
Electric Safety.) 

Electric Saw. — (See Saw, Electric? 



Ele. 



190 



[Ele. 



Electric Seismograph. — (See Seismo- 
graph, Electric.) 

Electric Shadow.— (See Shadow, Elec- 
tric.) 

Electric Shock. — (See Shock, Electric.) 

Electric Shower Bath. — (See Bath, 
Shower Electric.) 

Electric Shunt Bell.— (See Bell, Shunt, 
Electric.) 

Electric Single-Stroke Bell.— (See Bell, 
Single-Stroke Electric) 

Electric Siphon. — (See Siphon, Electric) 

Electric Soldering. — (See Soldering, 
Electric) 

Electric Sphygmograph. — (See Sphygmo- 
graph, Electrical.) 

Electric Sterilization. — (See Steriliza- 
tion, Electric) 

Electric Storm. — (See Storm, Electric.) 

Electric Striae. — (See Strice, Electric) 

Electric Submarine Boat. — (See Boat, 
Submarine, Electric) 

Electric Sunstroke. — (See Sunstroke, 
Electric) 

Electric Surgings. — (See Surgings, Elec- 
tric) 

Electric Swaging. — (See Swaging, Elec- 
tric) 

Electric Tanning. — (See Tanning, Elec- 
tric.) 

Electric Target. — (See Target, Electric) 

Electric Teazer. — (See Teazer, Electric 
Current) 

Electric Telehydrobarometer. — (See Tel- 
ehydrobaro7neter, Electric) 

Electric Tell-Tale Signal.— (See Signal, 
Electric Tell-Tale) 

Electric Tempering. — (See Tempering, 
Electric.) 

Electric Tension. — (See Tension, Elec- 
tric) 

Electric Thermo-Call. — (See Thermo- 
Call, Electric) 

Electric Thermometer. — (See Thermom- 
eter, Electric) 



Electric Throwback-Indicator. — ( See 

Indicator, Electrical Throwback) 

Electric Time-Ball.— (See Ball, Electric 
Time) 

Electric Time-Meter. — (See Meter, Elec- 
tric Time) 

Electric Torpedo. — (See Torpedo, Elec- 
tric) 

Electric Tower. — (See Tower, Electric) 
Electric Tramway. — (See Trajnway, Elec- 
tric) 

Electric Transmitters. — (See Transmit- 
ter, Electric) 

Electric Trumpet. — (See Trumpet, Elec- 
tric) 

Electric Turn-Table— (See Turn-Table, 
Electric) 

Electric Typewriter. — (See Typewriter, 
Electric) 

Electric Yalve. — (See Valve, Electric) 

Electric Yalve Burner, Argand 

(See Valve Burner, Argand Electric) 

Electric Varnish. — (See Varnish, Elec- 
tric) 

Electric Yibrating Burner. — (See Burner t 
Vibrating, Electric) 

Electric Volatilization. — (See Volatiliza- 
tion, Electric) 

Electric Water or Liquid Level Alarm.— 

(See Alarm, Water or Liquid Level) 

Electric Welding. — (See Welding, Elec- 
tric) 
Electric Whirl.— (See Whirl, Electric) 
Electric Whistle, Automatic Steam 

— (See Whistle, Steam, Aictomatic Elec- 
tric?) 

Electric Wood Mouldings. — (See Mould- 
ings, Electric Wood) 

Electric Work. — (See Work, Electric) 

Electrical Controlling Clock. — (See 
Clock, Electrical Controlling) 

Electrically. — In an electrical manner. 

Electrically Controlled Clock. — (See 
Clock, Electrically Controlled) 



Ele.] 



191 



[Ele. 



Electrically Discharge, To (See 

Discharge, To Electrically?) 

Electrically Discharging.— (See Dis- 
charging, Electrically?) 

Electrically Energizing.— (See Energiz- 
ing, Electrically?) 

Electrically Operated Alarm. — (See 
Alarm, Electrically Operated?) 

Electrically Retarding.— (See Retard- 
ing, Electrically?) 

Electrician. — One versed in the principles 
and applications of electrical science. 

Electrician, Electro-Therapeutical 

— A medical electrician. 

Electrician, Medical One skilled 

in the application of electricity to the human 
body for diagnosis or curative purposes. 

A medical electrician should possess a full 
knowledge, not only of the principles and appli- 
cations of electric science, but also of physics and 
chemistry and of the medical sciences. 

Electricity. — The name given to the un- 
known thing, matter or force, or both, which 
is the cause of electric phenomena. 

Electricity, no matter how produced, is be- 
lieved to be one and the same thing. 

The terms frictional '-electricity , pyro-electricity, 
magneto-electricity, voltaic or galvanic electricity, 
thermo-electricity, contact-electricity, animal or 
vegetable-electricity , etc., etc., though convenient 
for distinguishing their origin, have no longer 
the significance formerly attributed to them as 
representing different kinds of the electric force. 
(See Electricity, Single-Fluid Hypothesis of. ) 

Electricity, Accumulated — Elec- 
tricity collected in or by means of accumula- 
torsc 

Electricity, Accumulating — Ob- 
taining successively increasing electrical 
charges. (See Electricity, Acciwiulation of?) 

Electricity, Accumulation of A 

general term applied indifferently to — 

(i.) The gradual collecting of electric 
energy in a Leyden jar or condenser. 

(2.) The increase of an electric charge by 
the action of various devices called accumu- 
lators. 



(3.) The production of a charge by the use 
of machines called influence machines. 

(4.) The collection of electric energy in the 
so-called storage batteries or accumulators. 

Electricity, Animal — Electricity 

produced during life in the bodies of animals. 

All animals produce electricity during life. In 
some, such as the electric eel or torpedo, the 
amount is comparatively large. In others, it is 
small. 

Some of these animals, when of full size, are able 
to give very severe shocks, and use this curious 
power as c means of defense against their enemies. 

If the spinal cord of a recently killed frog be 
brought into contact wilh the muscles of the 
thigh, a contraction will ensue.— (Matteucci.) 

The nerve and muscle of a frog, connected 
by a water contact with a sufficiently delicate 
galvanometer, show the presence of a current 
that may last several hours. Du Bois-Reymond 
showed that the ends of a section of muscular 
fibres are negative, and their sides positive, and 
has obtained a current by suitably connecting 
them. 

In the opinion of some electro-therapeutists no 
electric current exists in passive, normal nerve or 
muscular tissue. In an injured tissue a current, 
called a demarcation current, is produced. (See 
Current, Demarcation?) 

All muscular contractions, however, apparently 
produce electric currents. 

In electro-therapeutics, it is probable that 
greater success would accrue in practice if the 
human body were regarded as an electric source 
as well as an electro-receptive device. 

Electricity, Atmospheric The free 

electricity almost always present in the atmos- 
phere. 

The following facts have been discovered con- 
cerning atmospheric electricity, viz.: 

(1.) The free electricity of the atmosphere is 
generally positive, but often changes to negative 
on the approach of fogs and clouds. 

(2.) It exists in greater quantity in the higher 
regions of the air than near the earth's surface. 

(3.) It is stronger when the air is still than 
when the wind is blowing. 

(4.) It is subject to yearly and daily changes 
in its intensity, being stronger in winter than in 
summer, and at the middle of the day than either 
at the beginning or the close. 



file.] 



192 



[Ele. 



Electricity, Atmospheric, Origin of 

■ — The exact cause of the free electricity of 
the atmosphere is unknown. 

Peltier ascribes the cause of the free electricity 
of the atmosphere to a negatively excited earth, 
which charges the atmosphere by induction. (See 
Induction, Electrostatic.) Free atmospheric elec- 
tricity has also been ascribed to the evaporation 
of water; to the condensation of vapor; to the 
friction of the wind; to the motion ot teirestrial 
objects through the earth's magneiic fit Id; to in- 
duction from the sun and other heavenly bodies; 
to differences of temperature; to combustion, and 
to gradual oxidation of plant and animal life. It 
is possible that all these causes may have some 
effect in producing the fiee electricity of the at- 
mosphere. 

Whatever is the cause of the free electricity of the 
atmosphere, there can be but little doubt that it 
is to the condensation of aqueous vapor that the 
high difference of potential of the lightning flash 
is due. (See Potential, Difference of.) As the 
clouds move through the air they colli ct the free 
electricity on the surfaces of the minute drops of 
water of which they are composed, ai,d when 
many thousands of these subsequently collect in 
larger drops the difference of potential is enor- 
mously increased in consequence of the equally 
enormous decrease in the surface of any single 
drop over the sum ot the surfaces of the drops 
that have coalesced to form it. 

Electricity, Atom of A quantity 

of electricity equal in amount to that pos- 
sessed by any chemical monad atom. 

Professor Lodge points out the fact that the 
charge of a monad atom of any element is the 
smallest charge a body can possess, and i> possibly 
as indivisible as the atom itself. He points out the 
fact that chemical affinity or atomic attraction may 
bedue to the electrical attraction of atoms contain- 
ing unlike charges; that although the difference of 
potential between the atoms is small, probably 
somewhere between I and 3 volts, the distances 
separating them are so very small that their 
mutual attractive force must be almost infinitely 
great. 

As DAuria has pointed out, if the centres of at- 
traction of the at^ms be the cc tre^ of the 
atoms themselves, then the atom=, if approached 
to actual contact, would be separated from one 
another by a distance equal to half the sum of 
their diameters. If, however, the centre of at- 



traction be situated at any point on the surface of 
the atoms the distance of separation would be- 
come equal to zero, calling d, th6 distance be- 
tween them, m and m 1 , their respective masses, 
and S, a co-effecient varying with the substance, 
and f, the force of mutual attraction, then : 



/m m'\ 



from which we see that the value of i x becomes 

infinite when the atoms are in contact. 

Electricity, Cal — Electricity pro- 
duced by changes of temperature in the core 
of a transformer. 

The changes of temperature in the transformer 
core can produce a difference of potential in the 
secondary circuit which increases the electro- 
motive force induced in the secondary by the 
variations in the primary. This is sometimes 
called the Acheson effect. (See Effect, Acheson.) 

Electricity, Conservation of — A 

term proposed by Lippman to express the 
fact that when a body receives an electric 
charge in the open air, the earth and heavenly 
bodies receive an equal and opposite charge, 
thus preserving the sum of the total positive 
and negative electricities in the universe, 

Electricity, Contact — Electricity 

produced by the mere contact of dissimilar 
metals. 

Th^ mere contact of two dissimilar metals re- 
sults in the production of opposite electrical 
charges on their opposed surfaces, or in a differ- 
ence of electric potential between these surfaces. 
The cause of this difference of potential is now 
very generally ascribed to the voltaic couple being 
surrounded by the atmosphere, the oxygen of 
which acts more energetically on the positive 
element than it does on the negative element. 

The mere contact of dissimilar metals cannot 
produce a constant electric current. An electric 
current possesses kinetic energy. To produce a 
constant electric current, therefore, energy must 
be expended. 

The voltaic pile through the contact of dis- 
similar metals produces a difference of potential, 
yet the cause of the current is to be found in 
chemical action. (See Cell, Voltaic.) 

Electricity, Disguised - Dissimu- 
lated electricity. (See Electricity, Dissimu- 
lated or Latent?) 



EleJ 



193 



[Ele, 



Electricity, Dissimulated or Latent 

—The condition of an electric charge when 
placed near an opposite charge, as inaLeyden 
jar or condenser. 

In this case, merely touching one of the 
charged surfaces will not effect its complete dis- 
charge. 

Electricity in the condition of a bound charge 
was formerly called latent electricity. This term 
is now in disuse. Such a charge is now called a 
bound charge. (See Charge, Bound. Charge, 
Free.) 

Electricity, Distribution of —Va- 
rious combinations of electric sources, circuits 
and electro-receptive devices whereby elec- 
tricity generated by the sources is carried or 
distributed to more or less distant electro- 
receptive devices by means of the various cir- 
cuits connected therewith. 

A number of different sys f ems for the distribu- 
tion of electricity exist. Among the most import- 
ant are the following, viz. : 

(i.) Direct or continuous-current distribution. 

(2.) Alternating-current distribution. 

(3.) Storage battery or secondary distribution. 

(4.) Distribution by means of condensers. 

(5.) Distribution by means of motor-gener- 
ators. 

Electricity, Distribution of, by Alterna- 
ting Currents A system of electric 

distribution by the use of alternating currents. 

A system of electric distribution in which 
lamps, motors, or other electro-receptive de- 
vices are operated by means of alternating 
currents that are sent over the line, but which, 
before passing through said devices, are modi- 
fied by apparatus called transformers or con- 
verters. 

Such a system embraces : 

(1.) An alternating-current dynamo-electric 
machine or battery of machines. 

(2.) A conductor or line wire arranged in a 
metallic circuit. 

(3.) A number of converters or transformers 
whose primary coils are placed in the circuit of 
the line wire. 

(4.) A number of electro-receptive devices 
placed in the circuit of the secondary coil of the 
converter. (See Transformer.) 



Electricity, Distribution of, by Alterna- 
ting Currents by Means of Condensers 

- — A system of alternate current distribution 
in which condensers are employed to trans- 
form current of high potential, received from 
an alternating current dynamo, to currents 
of low potential which are fed to the lamps or 
other electro-receptive devices, 

In the system of McElroy the conversion from 
high to low potential is obtained 1 y making the 
primary plates of the condensers charged by 
the dynamo smaller than the secondary plates, 
the ratio of the area of the primary plates to that 
of the secondary plates being made in accordance 
with the ratio of conversion desired. 

Electricity, Distribution of, by Commuta- 
ting" Transformers A system of elec- 
trical distribution in which motor-generators 
are used, but neither the armature nor the 
field magnets are revolved, a special commu- 
tator being employed to change the polarity 
of the magnetic circuits. 

Electricity, Distribution of, by Constant 

Currents A system for the distribution 

of electricity by means of direct, /. e., con- 
tinuous, steady or non-alternating currents, 
as distinguished from alternating currents. 

Distribution by means of direct currents may 
be effected in a number of ways ; the most im- 
portant are: 

(1.) Distribution with constant current or 
series - distribution . 

(2.) Distribution with constant fotential or 
multiple-distribution. 

Strictly speaking, these, as, indeed, all systems, 
are systems for the distribution of electric energy 
rather than the distribution of electricity. 

In a system of series -distribution, the electro- 
receptive devices are placed in the main line in 
series, so that the electric current passes succes- 
sively through each of them. In such a system 
each device added increases the total resistance of 
the circuit so that the total resistance is equal to 
the sum of the separate resistances on the line. 

In order, therefore, to maintain the current 
strength constant, independent of the number of 
devices added to or removed from the circuit, the 
electromotive force of the source must increase 
with each electro-receptive device added, and de- 
crease with each electro-receptive device taken 



He.] 



194 



[Ele. 



out. If the number of electro-receptive devices 
be great, such a circuit is necessarily character- 
ized by a comparatively high electromotive force. 

Since the current passes successively through 
all the electro-receptive devices, an automatic 
safety device is necessary in order to automatically 
provide a short circuit of comparatively low resist- 
ance past a faulty device, and thus prevent a 
single faulty device from invalidating the action 
of all other devices in the circuit. 

Arc lamps are usually connected to the line 
circuit in series. 

In a system oimultiple- distribution, the electro- 
receptive devices are connected to the main line 
or leads in multiple-arc, or parallel, so that each 
device added decreases the resistance of the circidt. 
In order, therefore, to maintain a proper current 
through the electro-receptive devices, the mains 
must be kept at a nearly constant difference of 
potential. The electro-receptive devices employed 
in such a system of distribution are generally of 
high electric resistance, so that the introduction or 
removal of a few of the electro-receptive devices 
will not materially alter the resistance of the whole 
circuit, and will not, therefore, materially affect 
the remaining lights. 

In this system automatic safety devices, opera- 
ting by the fusion of a readily melted alloy or 
metal, are provided for the purpose of preventing 
too powerful currents from passing through any 
branch connected with the main conductors or 
leads. (See Plug, Fusible.') 

Incandescent lamps are generally connected 
with the main conductors or leads in parallel or 
multiple-arc. 

Distribution of incandescent lamps by series 
connections is sometimes employed. Such lamps 
are usually of comparatively low resistance, and 
are provided each with an automatic cut-out, 
which establishes a short circuit past the lamp on 
its failure to properly operate. 

During the passage of an electric current 
through any series-distribution circuit, energy is 
expended in different portions of the circuit, in 
proportion to the resistance of these parts. In 
any system, economy of distribution necessitates 
that the energy expended in the electro-receptive 
devices must bear as large a proportion as prac- 
ticable to the energy expended in the source and 
leads. In series-distribution, this can readily be 
accomplished even if the resistance of the leads is 
comparatively high, since the total resistance of 
the circuit increases with every electro-receptive 



device added. Comparatively thin wires can 
therefore be employed for a very considerable 
extent of territory covered, without very great 
loss. 

In systems of multiple-distribution, however, 
this is impossible ; for, since every electro-recep- 
tive device added decreases the total res.stance of 
the circuit, unless the resistance of the leads is 
correspondingly decreased the economy becomes 
smaller, unless the resistance of the leads was orig- 
inally so low as to be inappreciable when com- 
pared with the change of resistance. 

In systems of distribution by alternating cur- 
rents this is avoided by passing a current of but 
small strength and considerable difference of 
potential over a line connecting distant points, 
and converting this current into a current oflarge 
strength and small difference of potential at the 
places where it is required for use. 

Electricity, Distribution of, Tby Contin- 
uous Current, by Means of Condensers 

A system of distribution devised by 

Doubrava, in which a continuous current is 
conducted to certain points in the line where 
a device called a " disjunctor " is employed, to 
reverse it periodically, and the reversed cur- 
rents so obtained directly used to charge con- 
densers in the circuit of which induction coils 
are used. 

This method of distribution is a variety of dis- 
tribution by means of constant currents. 

The condensers are used to feed incandescent 
lamps or other electro-receptive devices. 

Electricity, Distribution of, by Continu- 
ous Current, by Means of Transformers 

■ — A system for the transmission of elec- 
tric energy by means of continuous or direct 
currents that are sent over the line to suitably 
located stations where motor-dynamos are 
used for transformers. 

The dynamo armature is used with two sepa- 
rate circuits, one of a short and coarse wire, and 
one of a long fine wire. This construction will 
permit the conversion of a high to a low potential 
or vice versa; or two separate dynamos can be 
placed on the same shaft and one used as the 
motor. 

It is evident that a motor generator can be con- 
structed to convert continuous currents into alter- 
nate, or alternate currents into continuous cur- 



Hie.] 



195 



[Ele. 



rents. In this last case the armature and fixed 
circuits must be kept separate. 

Another form of .continuous current conversion 
is effected by means of the motion of a commutator 
■which effects a rotation of magnetic polarity in a 
double- wound armature of fine and coarse wire. 

Electricity, Distribution of, by Motor 
Generators — A system of electric dis- 
tribution in which a continuous current of 
"high potential, distributed over a main line, is 
employed at the points where its electric en- 
ergy is to be utilized for driving a motor, 
which in turn drives a dynamo, the current of 
which is used to energize the electro-recep- 
tive devices. 

This method of distribution is a variety of dis- 
tribution by means of continuous or direct cur- 
rents. 

In another system of distribution by means of 
-motor generators, the motor and dynamo are 
combined in one with a double-wound arnature, 
the fine wire coils in which receive the high po- 
tential driving current and the coarse wire coils 
furnish the low potential current used in the dis- 
tribution circuits. 

Electricity, Double Fluid Hypothesis of 
A hypothesis which endeavors to ex- 
plain the causes of electric phenomena by the 
assumption of the existence of two different 
electric fluids. 

The double fluid hypothesis assumes: 

(i.) That the phenomena of electricity are due 
to two tenuous and imponderable fluids, the posi- 
tive and the negative. 

(2.) That the particles of the positive fluid repel 
one another, as do also the particles of the nega- 
tive fluid; but that the particles of positive fluid 
attract the particles of the negative and vice versa. 

(3.) That the two fluids are strongly attracted 
by matter, and when present in it produce elec- 
trification. 

(4.) That the two fluids attract one another and 
unite, thus masking the properties of each. 

(5.) That the act of friction separates these 
fluids, one going to the rubber and the other to 
the thing rubbed. 

Professor Lodge is disposed to favor the double 
rather than the single fluid hypothesis. He states 
in support of this belief the following facts, viz. : 

(1.) An electric wind or breeze is produced 
both at the positive and negative terminals of an 



electrical machine, and this whether the point be 
attached directly to these terminals, or whether 
it be held in the hand of a person near them. 

(2.) The well known peculiarities connected 
with the spark discharge, seen in Wheatstone's 
experiments on the velocity of electricity. 

(3.) An electrostatic strain scarcely affects the 
volume of the dielectric, thus suggesting or show- 
ing a distorting stress, which alters the shape of 
the substance of the dielectric, but not its size. 

(4.) The effects of electrolysis in what he as- 
sumes the double procession of the atoms past 
each other in opposite directions. 

(5.) The phenomena of self-induction, or the 
behavior of a thick wire on an alternating current. 

(6.) The apparent absence of momentum in the 
electric current, or moment of inertia in an elec- 
tro-magnet so far as tested. 

Electricity, Dynamic A term some- 
times employed for current electricity in con- 
tradistinction to static electricity. 

Electricity, Franklinic — A term 

sometimes employed in electro-therapeutics, 
for the electricity produced by a frictional 
or an electrostatic-induction machine. (See 
Current, Franklinic.) 

Electricity, Frictional Electricity 

produced by friction. 

This term as formerly employed to indicate 
static charges as distinguished from currents, is 
gradually falling into disuse, and the frictional 
electric machines are being generally replaced by 
continuous-induction machines, like those of 
Holtz, Topler-Holtz, or Wimshurst. 

The character of the charge produced by fric- 
tion depends on the nature of the rubber as well 
as on that of the thing rubbed. 

In the following table the substances are so ar- 
ranged that any one in the list becomes positively 
electrified when rubbed by any which follows it : 

Positive. 
Cat's fur. 
Polished glass. 
Wool. 

Cork at ordinary temperatures. 
Coarse brown paper. 
Cork heated. 
White silk. 
Black silk. 
Shellac. 
Rough glass. — {Forbes.) 



Ele.] 



196 



[Ele. 



Negative. 

It will be seen that the character of the charge 
produced by friction depends on the character of 
the surfaces rubbed. This is seen from the fore- 
going table, where — 

(i.) The roughness of the surface, as in the 
case of glass, produces a difference in the nature of 
the charge; thus, rough glass is at the bottom of 
the table, and smooth, polished glass near the top. 

(2.) The state of the surface as shown by the 
color. Black silk rubbed with white silk is nega- 
tive to it. 

(3.) The state of the surface, as varied by the 
temperature. Hot cork receives a negative charge 
when rubbed against a piece of cold cork. 

Forbes has pointed out that these differences 
are probably due to the change produced in the 
ability of the surface to radiate heat or light. A 
substance or body which radiates the most light 
or heat is negative. Thus, a hot body radiates 
more heat than a cold body, and is negative to it. 
A rough surface is negative to a smooth surface 
because it radiates more heat than a smooth sur- 
face. For the same reason a black surface is neg- 
ative to a white surface. In this latter case, how- 
ever, the black surface is the worse radiator of 
light. 

The contact of dissimilar substances has long 
been considered by some as one of the requisites 
for the ready production of electricity by friction. 
In fact, the production of electricity by friction 
has been ascribed as an effect due to a true contact 
force at the points of junction of the rubber and 
the thing rubbed. Others, however, deny the 
existence of a true contact force of this nature. 
(See Force, Contact.') 

Electricity, Galvanic A term used 

by some in place of voltaic electricity. (See 
Electricity, Voltaic^) 

The use of the term galvanic electricity would 
appear to be less logical than the word voltaic, 
since Volta, and not Galvani, was the first to find 
out the true origin of the difference of potential 
produced in the voltaic pile. 

Electricity, Hertz's Theory of Electro- 
Magnetic Radiations or Waves ■ — A 

theory, now generally accepted, which regards 
light as one of the effects of electro-magnetic 
pulsations or waves. 

The recent brilliant researches of Dr. Hertz, of 
Carlsruhe, show that when an impulsive discharge 



is passing through a conductor, ether waves are 
radiated or propagated in all directions in the 
space surrounding the conductor, and that these 
waves are in all respects similar to those of light, 
except that they are much longer. 

The electro-magnetic waves are set up in the 
luminiferous ether, and move through it with the 
same velocity as that of light. Moreover, electro- 
magnetic waves possess the same powers of reflec- 
tion, refraction, interference, resonance, etc., etc.,, 
as are possessed by waves of light. (See Resona- 
tor, Electric.') 

When an alternating or simple faradic current 
or pulse of electricity is transmitted from one end 
to the other of a long metallic conductor, the 
pulses are believed to travel through the universal 
ether surrounding the conductor rather than 
through the conductor itself. The velocity of this 
propagation in free ether is the same as that of 
light, and, indeed, is identical with that of light 
itself. In the inter-atomic or inter -molecular 
ether, whether of conductors, or of dielectrics, the 
velocity of propagation varies with the nature of 
the medium. 

The waves produced by electric pulses are of 
much greater length than those of light. 

According to Lodge a condenser of the capacity 
of a micro-farad, if discharged through a coil hav- 
ing the self-induction of I ohm, will give rise 
to waves in the ether 1,200 miles in length, and 
will possess a rate of oscillation equal to about 157 
complete wave-lengths per second. 

A common pint Leyden jar discharged through 
an ordinary discharging rod, will produce a se~ 
ries of waves about 15 to 20 metres in length, 
and will possess a rate of oscillation equal to about 
ten million per second. 

Lodge calculates that in order to obtain the short 
waves requisite to influence the retina of the eye, 
and thus produce light, the circviit in which the 
electrical oscillations take place must have at least 
atomic dimensions, and that the phenomena of 
light may therefore be due to local oscillations or 
surgings in circuits of atomic dimensions. (See 
Light, Maxwell' 's Electro-Magnetic Theory of.) 



-A term for- 



Electricity, Latent — 

merly applied to bound electricity. 

Electricity, Magneto 



Electricity 

produced by the motion of magnets past con- 
ductors, or of conductors past magnets. 
Electricity produced by magneto-electrics 



Ele.] 



197 



[Ele. 



induction. (See Induction, Electro-Dyna- 
mic?) 

Electricity, Multiple-Distribution of, by 
Constant Potential Circuit — Any 

system for the distribution of continuous cur- 
rents of electricity in which the electro- 
receptive devices are connected to the leads 
in multiple-arc or parallel. (See Electricity, 
Distribution of, by Constant Currents) 

Electricity, Natural Unit of —A 

term sometimes used in place of an atom of 
electricity. 

The natural unit of electricity is an amount 
equal to the charge possessed by any monad atom 
of a chemical element. 

The natural unit of electricity is equal to the 
hundred thousand millionth of the ordinary 
electrostatic unit, or less than a hundred tril- 
lionth of a coulomb. {See Electricity, A ton of .) 

Electricity, Negative One of the 

phases of electrical excitement. 

The kind of electric charge produced on 
resin when rubbed with cotton. 

Electricity, Photo Electrical dif- 
ferences of potential produced by the action 
of light 

Electricity, Plant Electricity pro- 
duced in plants during their growth. 

Electricity, Positive One of the 

phases of electric excitement. 

The kind of electric charge produced on 
cotton when rubbed against resin. 

Electricity, Production of, by Light 

— The production of electric differences of 
potential by the action of light. 

Hallwachs has noticed that a clean metallic 
plate becomes electrified when light falls upon it. 

Differences of potential are produced in a 
selenium cell when its electrodes are unequally 
illumined. A thermo cell is an illustration of a 
difference of potential produced by non-luminous 
radiation. 

Electricity, Pyro Electricity de- 
veloped in certain crystalline bodies by un- 
equally heating or cooling them. 

Tourmaline, in the crystalline state, possesses 
this property in a marked degree. When a 
crystal of tourmaline is heated or cooled, it 




v^ 




Fig. 



227 . Pyro -Electric 
Crystal. 



acquires opposite electrifications at opposite 
ends or poles. 

In the crystal of tourmaline shown in Fig. 227, 
the end A, called the analogous pole, acquires a 
positive electrification, 
and the end B, called the 
antilogous pole, a nega- 
tive electrification, while 
the temperattire of the 
cry stalls rising. While 
cooling, the opposite 
electrifications are pro- 
duced. 

A heated crystal of 
tourmaline, suspended by 
a fibre, is attracted or 
repelled by an electrified 
body or by a second 
heated tourmaline, in the 
same manner as an elec- 
trified body. 

Many crystalline bodies possess similar prop- 
erties. Among these are the ore of zinc known 
as electric calamine or the silicate of zinc, bora- 
cite, quartz, tartrate of potash, sulphate of 
quinine, etc. 

Electricity, Radiation of — The 

radiation of electric energy by means of elec- 
tro-magnetic waves. (See Electricity, Hertz's 

Theory of Electro-Magnetic Radiations or 

Waves) 

Electricity, Eesinous A term 

formerly employed in place of negative elec- 
tricity. 

It was at one time believed that all resinous 
substances are negatively electrified by friction. 
This we now know to be untrue, the nature of 
electrification depending as much on the char- 
acter of the rubber as on the character of the 
thing rubbed. Thus resins rubbed with cotton, 
flannel or silk, become negatively excited, but when 
rubbed with sulphur or gun cotton, positively 
excited. The terms positive and negative are 
now exclusively employed. 

Electricity, Series Distribution of, by 
Constant Current Circuit Any sys- 
tem for the distribution of constant currents 
of electricity in which the electro-receptive 
devices are connected to the line-wire or 
circuit in series. (See Electricity, Distribu- 
tion of, by Constant Currents) 



Ele.] 



198 



[Ele. 



Electricity, Single-Fluid Hypothesis of 

A hypothesis which endeavors to ex- 



plain the cause of electrical phenomena by 
the assumption of the existence of a single 
electric fluid. 

The single-fluid hypothesis assumes: 

(i.) That the phenomena of electricity are due 
to the presence of a single, tenuous, imponder- 
able fluid. 

(2 ) That the particles of this fluid mutually 
repel one another, but are attracted by all matter. 

(3.) That every substance possesses a definite 
capacity for holding the assumed electric fluid, 
and, that when this capacity is just satisfied no 
effects of electrification are manifest. 

(4.) That when the body has less than this 
quantity present, it becomes negatively excited, 
and when it has more, positively excited. 

(5 . ) That the act of friction causes a redistribu- 
tion of the fluid, part of it going to one of 
the bodies, giving it a surplus, thus positively 
electrifying it, and leaving the other with a 
deficit, thus negatively electrifying it. 

The single-fluid hypothesis has been provis- 
ionally accepted by some with this modification, 
that a negatively excited body is thought to be 
the one wtich contains the excess of the assumed 
fluid, and a positively excited body the one which 
contains the deficit. 

They make this change on account of the 
phenomena observed in Crookes' tube, where 
the molecules of the residual gas are observed to 
be thrown off from the negative and not from the 
positive terminal. (See Tube, Crookes\) 

Another view considers electricity to be due to 
differences of ether pressure, electricity being the 
ether itself, and electromotive force, the differences 
of ether pressures. Positive electrification is as- 
sumed to result from a surplusage of energy, and 
negative electrification from a deficit of energy. 

At the present time the views of Hertz are 
generally accepted. (See Electricity, Hertz's 
Theory of Electro-Magnetic Radiations or Waves.') 

Electricity, Specific Heat of A 

term proposed by Sir William Thomson to 
indicate the analogies existing between the 
absorption and emission of heat in purely 
thermal phenomena, and the absorption and 
emission of heat in thermo-electric phe- 
nomena. (See Heat, Specific^ 
As we have already seen heat is either given 



out or absorbed, when an electric current passes 
from one metal to another across a junction be- 
tween them. (See Effect, Peltier.) 

So, too, when electricity passes through an un- 
equally heated wire, the current tends to increase 
or decrease the differences of temperature, ac- 
cording to the direction in which it flows, and 
according to the character of the metal. (See 
Effect, Thomson.) 

" If electricity were a fluid," says Maxwell, 
"running through the conductor as water does 
through a tube, and always giving out or ab- 
sorbing heat till its temperature is that of the 
conductor, then in passing from hot to cold it 
would give out heat, and in passing from cold to 
hot it would absorb heat, and the amount of this 
heat would depend on the specific heat of the 
fluid." 

Electricity, Static A term applied 

to electricity produced by friction. 

The term static electricity is properly em- 
ployed in the sense of a static charge but not as 
static electricity, since that would indicate a par- 
ticular kind of electricity, and, as is now gen- 
erally recognized, electricity, from no matter 
what source it is derived, is one and the same 
thing. 

Electricity, Storage of A term 

improperly employed to indicate such a 
storage of energy as will enable it to directly 
reproduce electric energy. 

A so-called storage battery does not store elec- 
tricity, any more than the spring of a clock can 
be said to store time or sound. The spring stores 
muscular energy, i. e., renders the muscular 
kinetic energy potential, which, again becoming 
kinetic, causes the works of the clock to move 
or strike. 

In the same way in a so-called storage battery, 
the energy of an electric current is caused to 
produce electrolytic decompositions of such a 
nature as independently to produce a current on 
the removal of the electrolyzing current. (See 
Cell, Secondary. Cell, Storage.) 

Electricity, Thermo Electricity 

produced by differences of temperature at the 
junctions of dissimilar metals. 

If a bar of antimony is soldered to a bar of bis- 
muth, and the free ends of the two metals are 
connected by means of a galvanometer, an appli- 
cation of heat to the junction, so as to raise its 



Ele.] 



199 



[Ele. 



temperature above the rest of the circuit, will pro- 
duce a difference of potential, which, if neutral- 
ized, will cause a current to flow across the junc- 
tion from the bismuth to the antimony (against 
the alphabet, or from B to A). If the junction be 
cooled below the rest of the circuit, a current is 
produced across the junction from the antimony 
to the bismuth (with the alphabet, or from A to B). 
These currents are called thermo-electric currents, 
and are proportional to the differences of tem- 
perature. 

Even the same metal, in different physical 
states or conditions, such as a wire, part of which 
is straight and the remainder bent into a spiral as 
at H C, Fig. 228, if heated at F by the flame of 
F 




Fig. 228. Thrrmo- Electricity. 

a lamp will have a difference of potential devel- 
oped in it. 

The same thing may also be shown by placing 
a cylinder of bismuth J, Fig. 229, in a gap in a 




Fig. 22Q. Thermo-Electric Circuit. 

hollow rectangle of copper A B, inside of which 
a magnetic needle, M, is supported. 

The rectangle of copper being placed in the 
magnetic meridian, on heating the junction by the 
flame of a lamp F, the needle will be deflected 
by a current produced by the difference of tem- 
perature. 

Thermo-electricity is generally obtained by 
means of the combination of a thermo-electric 
tonple, in a thermo-electric cell. (See Couple, 
Thermo-Electric. Cell, Thermo-Electric.') 

Since the difference of potential produced by 
a single thermo-electric couple is small, a number 
of such couples or cells are generally connected in 



series to produce a thermo-electric battery. (See 
Battery, Thermo-Electric.} 

Electricity, Unit Quantity of — 

The quantity of electricity conveyed by unit 
current per second. 

The practical unit quantity of electricity is the 
coulomb, which is the quantity conveyed by a 
current of one ampere in one second. 

Electricity, Unit Quantity of, Natural 
— The quantity of electricity pos- 
sessed as a charge by any elementary monad 
atom. (See Electricity, Ato7n of.) 

Electricity, Tarieties of — A classi- 
fication of electricity according to its state of 
rest or motion, or to the peculiarities of its 
motion. 

Lodge classifies the different varieties of elec- 
tricity as follows, viz.: 

(1.) Electricity at Rest, or Static Electricity. 

This branch of electric science treats of phenom- 
ena belonging to stresses and strains in insulated 
media, when brought into the neighborhood of 
electric charges, together with the modes of ex- 
citing such electric charges, and the laws of their 
interactions. 

(2.) Electricity in Locomotion, or Current Elec- 
tricity. 

This branch of electric science treats of the phe- 
nomena produced in metallic conductors, chem- 
ical compounds and dielectric media, by the pas- 
sage of electricity through them, and the modes 
of exciting electricity into motion, together with 
the laws of its flow. 

(3.) Electricity in Rotation, or Magnetism. 

This branch of electric science treats of the phe- 
nomena produced in electricity in whirling or 
vortex motion, the manner in which such whirls 
may be produced, the strains and stresses which 
they produce, and the laws of their interactions. 

(4.) Electricity in Vibration, or Radiation. 

This branch of electric science treats of the study 
of the propagation of periodic or undulatory dis- 
turbances through various kinds of media, the 
laws regulating wave velocity, wave length, re- 
flection, interference, dispersion, polarization and 
other similar phenomena generally studied under 
light. 

A misleading classification of electricity is 
sometimes made according to the sources which 
produce it. This is misleading, since electricity, 
no matter how produced, is one and the same. 



Ele.] 



200 



[Ele.. 



The so-called varieties of electricity may be di- 
vided into different classes according to the nature 
of the source. The principles of these are as fol- 
lows : 

(i.) Frictional-Electricity, or that produced by 
the friction of one substance against another. 

(2.) Voltaic-Electricity, or that produced by 
the contact of dissimilar substances under the in- 
fluence of chemical action. 

(3.) Thermo-Electricity, or that produced by 
differences of temperature in a thermo couple. 

(4.) Pyro-Electricity, or that produced by dif- 
ferences of temperature in certain crystalline 
solids. 

(5.) Magneto-Electricity, or that produced by 
the motion of a conductor through the field of 
permanent magnets. This is a variety of — 

(6.) Dynamo-Electricity, or that produced by 
moving conductors so as to cut lines of magnetic 
force. 

(7.) Vital-Electricity, or that produced under 
the influence of life or accompanying life. 

Electricity, Vitreous — A term for- 
merly employed to indicate positive elec- 
tricity. 

It was formerly believed that the friction of 
glass with other bodies always produces the 
same kind of electricity. This, however, is now 
known not to be the case. 

The term is now replaced by positive elec- 
tricity. (See Electricity, Resinous.) 

Electricity, Voltaic —Differences of 

potential produced by the agency of a vol- 
taic cell or battery. 

Electricity is the same thing or phase of energy 
by whatever source it is produced. 

Electrics. — Substances capable of becom- 
ing electrified by friction. 

Substances like the metals, which, when held 
in the hand could not be electrified by friction 
were formerly called non-electrics. 

These terms were used by Gilbert in the early 
history of the science. 

This distinction is not now generally employed 
since conducting substances if insulated, may be 
electrified by friction. 

Electrifiable. — Capable of being endowed 
with electric properties. 

Electrification.— The act of becoming 
electrified. 

The production of an electric charge. 



Electrified Body.— (See Body, Electri- 
fied?) 

Electrify. — To endow with electrical prop- 
erties. 

Electrine. — Relating to electrum, or am- 
ber. 

Electrization, Therapeutical Sub- 
jecting different parts of the human body to 
the action of electric currents for the cure of 
diseased conditions. 

Electro-Biology. — (See Biology, Electro?) 

Electro-Brassing. — (See Brassing, Elec- 
tro?) 

Electro-Bronzing". — (See Bronzing, Elec- 
tro.) 

Electro • Capillary Phenomena. — (See 
Phenomena, Electro-Capillary?) 

Electrocesis.— A word proposed for cur- 
ing by electricity. 

Electro-Chemical Equivalent. — (See 
Equivalent, Electro-Chemical.) 

Electro-Chemical Meter. — (See Meter,. 
Electro- Ch em ica I.) 

Electro-Chemical Telephone. — (See Tele- 
phone, Electro-Chemical?) 

Electro-Chemistry. — (See Chemistry, 
Electro?) 

Electro-Chromic Ring's. — (See Rings, 
Electro- Ch rom ic .) 

Electro-Contact Mine. — (See Mine, Elec- 
tro-Contact?) 

Electro-Coppering". — (See Coppering, 
Electro?) 

Electro-Crystallizat ion. — (See Crystalli- 
zation, Electro?) 

Electrocution. — Capital punishment by 
means of electricity. 

Electrode. — Either of the terminals of an 
electric source. 

The term was applied by Faraday to either of 
the conductors placed in an electrolytic bath and 
conveying the current into it, and this is its strict: 
meaning. The terms pole or terminal apply to 
the ends of a break in any electric circuit. 

Electrode, Aural A therapeutic 

electrode, shaped for the treatment of the 



Ele.] 



201 



[Ele. 



ear. (See Electrode, Electro-Thera- 
peutic^) 

Electrode, Brush A therapeutic 

electrode fashioned like a wire brush or other 
conducting brush. (See Electrode, Electro- 
Therapeutic?) 

Electrode, Cautery-Knife A knife- 
shaped electrode, that is rendered incan- 
descent by the passage of the electric cur- 
rent. 

Electrode, Clay A therapeutic elec- 
trode of clay shaped to fit the part of the 
body to be treated. (See Electrode, Electro- 
Therapeutic?) 

Electrode, Disc A disc-shaped elec- 
trode employed in electro-therapeutics. (See 
Electrode, Electro- Therapeutic?) 

Electrode, Dry A therapeutic elec- 
trode applied in a dry state. (See Electrode, 
Electro- Therapeutic?) 

Electrode, Electro-Therapeutic 

In electro-therapeutics the electrode mainly 
concerned in the treatment or diagnosis of the 
diseased parts. 

Either the positive or the negative electrode 
may be the therapeutic electrode, and one or the 
other is employed according to the particular 
character of the effect it is desired to obtain. 
The other electrode is placed at any convenient 
and suitable part of the body, and is called the 
indifferent electrode. 

The therapeutic electrode is generally placed 
nearer the organ or part to be treated than the 
indifferent electrode. 

Electrode-Handle, Pole-Changing* and 

Interrupting- A handle provided for 

the ready insertion of electro-therapeutic 
electrodes, and provided with means for inter- 
rupting or changing the direction of the cur- 
rent. 

Electrode, Illumined That elec- 
trode of a selenium cell which is exposed to 
the light. (See Cell, Selenium?) 

Electrode, Indifferent In electro- 
therapeutics the electrode that is employed 
merely to complete the circuit through the 
organ or part subjected to the electric cur- 



rent, and is not directly concerned in the 
treatment or diagnosis of the diseased parts. 
Either the positive or the negative electrode 
may be the indifferent electrode. (See Electrode, 
Electro- Therapeutic.) 

Electrode, Moist A therapeutic- 
electrode applied in a moist condition. (See 
Electrode, Electro- Therapeutic?) 

Electrode, Needle A therapeutic 

electrode in the shape of a needle, and em- 
ployed for electrolytic treatment. (See Elec- 
trode, Electro- Therapeutic?) 

Electrode, Negative The electrode 

connected with the negative pole of an elec- 
tric source. 

Electrode, Non-Illumined — That 

electrode of a selenium cell that is protected 
from the direct action of light. (See Cell, Sel- 
enium?) 

Electrode, Non-Wasting- A term 

sometimes applied to the negative electrode 
of an arc-lamp when made of iridium or other 
similar material. 

Electrode, Positive The electrode 

connected with the positive pole of an electric 
source. 

Electrode, Rectal A therapeutic 

electrode, suitably shaped for the treatment of 
the rectum. [See. Electrode, Electro-Thera- 
peutic.) 

Electrode, Spong-e A moistened 

sponge connected to one of the terminals of 
an electric source and acting as the electro- 
therapeutic electrode. 

Electrode, Urethral An electro- 
therapeutic electrode suitably shaped for the 
treatment of the urethra. (See Electrode, 
Electro- Therapeutic.) 

Electrode, Yag-inal — An electro- 
therapeutic electrode suitably shaped for the 
treatment of the vagina. (See Electrode, 
Electro- Therapeutic?) 

Electro-Deposits. — (See Deposits, Elec- 
tro?) 

Electrodes. — The terminals of an electric 
source. 

The positive electrode is sometimes called the 



Eie.] 



202 



[Ele. 



Anode, and the negative electrode the Kathode. 
No matter for what purposes employed, they are 
generally in electro-therapeutics termed electrodes. 
In precise use these terms should be restricted 
to the electrodes when used for electrolytic de- 
composition. 

The electrodes are made of different shapes and 
of different materials according to the character of 
the work the current is to perform. 

Electrodes, Carbon, for Arc-Lamps 

Rods of artificial carbon employed in arc 
lamps. 

These are more properly called simply arc- 
lamp carbons. 

Arc-lamp carbons are moulded into the shape 
of rods, from plastic mixtures of carbonaceous 
materials and carbonizable liquids. On the sub- 
sequent carbonization of these rods the ingredients 
are caused to cohere in one solid mass by the de- 
posit of carbon derived from the carbonizable 
materials. (See Carbons* Artificial.') 

Carbons for arc-lamps are generally copper- 
coated, so as to somewhat decrease their resist- 
ance, and insure a more uniform consumption. 
Arc-lamp carbons are sometimes provided with a 
central core of softer carbon, which fixes the po- 
sition of the arc and thus insures a steadier light. 
(See Carbons, Cored.) 

Electrodes, Cored Carbon elec- 
trodes of a cylindrical shape provided with a 
central cylinder of softer carbon. 

The use of cored electrodes for arc lamps is 
for the purpose of steadying the light by maintain- 
ing the arc in a central position. This is effected 
by the greater vaporization of the softer carbon 
of the core. 

Electrodes, Cylindrical Carbon 

Carbon cylinders used for electrodes of arc- 
lamps, or for battery plates. 

Electrodes, Electro-Therapeutic 

Electrodes of various shapes employed in 
electro-therapeutics. 

The electro-therapeutic electrode, as distin- 
guished from the indifferent electrode, is especially 
shaped for the particular purpose for which it is 
designed. 

When the electricity is intended to affect the 
skin or superficial portions of the body only, it is 
applied dry, and is then generally metallic. To 
reach, the deeper structures, such as the muscle 
cr nerve trunks, moistened sponge electrodes are 



employed. Before their use the skin should be 
thoroughly moistened. Sponge-electrodes are 
generally made conducting by a solution of some 
saline substance, such as common salt. 

Electrodes, Erb's Standard Size of 

— Standard sizes of electrodes generally 
adopted in electro-therapeutics. 

The following standard sizes have been pro- 
posed by Erb, viz. : 

(i.) Fine electrode y 2 centimetre diameter. 

(2.) Small " 2 " « 

(3.) Medium " 7.5 " " 

(4.) Large " ...6x2 " " 

(5.) Very large do 8 x 16 " " 

Electrodes, Non-Polarizable — 

Electrodes employed in electro-therapeutics, 
that are so constructed as to avoid the effects 
of polarization. 

Non-polarizable electrodes are obtained by 
employing two amalgamated zinc wires, dipped 
into saturated solution of zinc chloride placed in 
glass tubes, and closing the lower ends of the 
tubes by a piece of potter's clay. The contact of 
an electrode so prepared with the tissues of the 
body does not produce a polarization. 

Electro-Diagnosis. — (See Diagnosis, Elec- 
tro?) 

Electro-Diagnostic. — (See Diagnostic, 
Electro?) 

Electro-Dynamic Attraction. — (See At- 
traction, Electro-Dynamic?) 

Electro-Dynamic Capacity. — (See Ca- 
pacity, Electro-Dynamic?) 

Electro-Dynamic Induction. — (See Induc- 
tion, Electro-Dynajnic.) 

Electro-Dynamic Repulsion. — (See Re- 
pulsion, Electro-Dynamic?) 

Electro-Dynamics. — (See Dyna7nics, 
Electro.) 

Electro-Dynan/ometer. — (See Dynamom- 
eter, Electro?) 

Electro-Etching.— Electric etching. (See 

Etching, Electro?) 

Electrogenesis. — Results following the 
application of electricity to the spinal cord or 
nerve after the withdrawal of the electrodes^ 



Electro-Gildin? 



■(See Gilding, Electro?? 



Ele.] 



203 



[Ele. 



Electro-Kinetics. — (See Kinetics, Elec- 
tro) 

Electrolier. — A chandelier for holding 
electric lamps, "as distinguished from a chan- 
delier for holding gas-lights. 

Electrology. — That branch of science 
which treats of electricity. (Obsolete.) 

Electrolysis. — Chemical decomposition 
effected by means of an electric current. 

When an electric current is sent through an 
electrolyte, i. e. , a liquid which permits the cur- 
rent to pass only by means of the decomposition 
of the liquid, the decomposition that ensues is 
called electrolytic decomposition. 

The electrolyte is decomposed or broken up 
into atoms or groups of atoms or radicals, called 
ions. 

The ions are of two distinct kinds, viz. : The 
electro-positive ions, or kathions, and the electro- 
negative ions, or anions. 

Since the anode of the source is connected with 
the electro-positive terminal, it is clear that the 
anions, or the electro-negative ions, must appear 
at the anode, and the kathions, or electro-positive 
ions, must appear at the kathode. 

Hydrogen, and the metals generally, are 
kathions. Oxygen, chlorine, iodine, etc., are 
anions. 

The vessel containing the electrolyte, in which 
these decompositions take place, is sometimes 
called an electrolytic cell. 

An electrolytic cell is called a voltameter when 
it is arranged for measuring the current passing 
by means of the amount of decomposition it 
effects. (See Voltameter.) 

Electrolysis toy Means of Alternating 
Currents. — Electrolytic decomposition ef- 
fected by means of alternating currents. 

When an alternating current is passed through 
dilute sulphuric acid, in a voltameter provided 
with large platinum electrodes, no visible decom- 
position occurs. If, however, the size of the 
electrodes be decreased below a certain point, 
then visible decomposition occurs. 

Verdet showed that when no other break ex- 
ists in the circuit of the alternating current 
within the voltameter, no indications of elec- 
trolysis are obtained, unless the alternating 
current is very powerful. If, however, a break is 
made in the secondary circuit, so that the dis- 



charge has to pass as a spark, then visible signs 
of electrolysis are produced by comparatively 
feeble alternating currents. 

When electrolysis occurs by means of alternat- 
ing currents— 

(i.) The gases collected at both electrodes 
have the same composition. 

(2.) Where the quantities of electricity that al- 
ternately pass in opposite directions are unequal, 
the electrodes show manifest polarization, and, 
when connected by a conductor, yield a current 
like a secondary battery. 

(3.) The electrodes manifest no sensible polari- 
zation where the quantities of electricity that al- 
ternately pass in opposite directions are equal. 

Electrolysis, Faraday's Laws of ■ 



The principal facts of electrolysis are given 
in the following laws: 

(1.) The amount of chemical action in any 
given time is equal in all parts of the circuit. 

(2.) The number of ions liberated in a given 
time is proportional to the strength of the cur- 
rent passing. Twice as great a current will 
liberate twice as many ions. The current may 
be regarded as being carried through the elec- 
trolyte by the ions: since an ion is capable of 
carrying a fixed charge only of -|- or — electri- 
city, any increase in the current strength necessi- 
tates an increase in the number of ions. 

(3.) When the same current passes successively 
through several cells containing different elec- 
trolytes, the weights of the ions liberated at the 
different electrodes will be equal to the strength 
of the current multiplied by the electro-chemical 
equivalent of the ion. (See Equivalence, Elec- 
tro-Chemical, Law of.) 

The chemical equivalent is proportional to the 
atomic weight divided by the valency. (See 
Equivalent, Chemical. ) 

The electro-chemical equivalent of any element 
is equal to the weight in grammes of that element 
set free by one coulomb of electricity, and is found 
by multiplying the electro-chemical of hydrogen 
by the chemical equivalent of that element. (See 
Equivalent, Electro- Chtmical. ) 

Electrolyte, Polarization of The 

formation of molecular groups or chains, in 
which the poles of all the molecules of any 
chain are turned in the same direction, viz.: 
with their positive poles facing the negative 
plate, and their negative poles facing the 



Ele.] 



204 



[Ele, 



positive plate. (See Cell, Voltaic. Hypoth- 
esis, Grotthus'.) 

Electrolytic or Electrolytical. — Pertain- 
ing to electrolysis. 

Electrolytic Analysis. — (See Analysis, 
Electrolytic) 

Electrolytic Cell.— (See Cell, Electro- 
lytic, Testa's?) 

Electrolytic Clock. — (See Clock, Electro- 
lytic) 

Electrolytic Conduction. — (See Conduc- 
tion, Electrolytic?) 

Electrolytic Convection. — (See Convec- 
tion, Electrolytic?) 

Electrolytic Decomposition. — (See De- 
composition, Electrolytic?) 

Electrolytic Hydrogen. — (See Hydrogen, 
Electrolytic?) 

Electrolytic Writing. — (See Writing, 
Electrolytic?) 

Electrolytically. — In an electrolytic man- 
ner. 

Electrolyzable. — Capable of being elec- 
trolyzed, or decomposed by means of elec- 
tricity. 

Electrolyzed. — Separated or decomposed 
by means of electricity. 

Electrolyzing. — Causing or producing 
electrolysis. 

Electro-Magnet. — (See Magnet, Electro?) 

Electro-Magnetic Ammeter. — (See Am- 
meter, Electro-Magnetic?) 

Electro-Magnetic Annunciator.— (See 
Annunciator, Electro-Magnetic?) 

Electro-Magnetic Attraction. — (See At- 
traction, Electro-Magnetic?) 

Electro-Magnetic Bell-Call.— (See Call, 
Bell, Magneto-Electric?) 

Electro-Magnetic Bell, Siemens' Arma- 
ture (See Bell, Electro-Magnetic, 

Siemens' Armature Form?) 

Electro-Magnetic Brake. — (See Brake, 
Electro-Magnetic?) 

Electro-Magnetic Cam. — (See Cam, 
Electro-Magnetic?) 



Electro-Magnetic Dental-Mallet. — (See 
Dental-Mallet, Electro-Magnetic?) 

Electro-Magnetic Drill. — (See Drill, 
Electro-Magnetic?) 

Electro-Magnetic Engine. — (See Engine, 
Electro-Magnetic?) 

Electro-Magnetic Exploder. — (See Ex- 
ploder, Electro-Magnetic?) 

Electro-Magnetic Eye. — (See Eye, Elec- 
tro-Magnetic?) 

Electro-Magnetic Impulse. — (See Im- 
pulse, Electro-Magnetic?) 

Electro-Magnetic Induction. — (See In- 
duction, Electro-Magnetic?) 

Electro-Magnetic Medium. — (See Me- 
dium, Electro-Magnetic?) 

Electro-Magnetic Meter. — (See Meter, 
Electro-Magn etic?) 

Electro-Magnetic Momentum of Sec- 
ondary Circuit. — (See Momentum, Elec- 
tro-Magnetic, of Secondary Circuit?) 

Electro-Magnetic Pop-Gun. — (See Pop- 
Gun, Electro-Magnetic.) 

Electro-Magnetic Radiation. — (See Ra- 
diation, Electro-Magnetic.) 

Electro-Magnetic Repulsion. — (See Re- 
pulsion, Electro-Magnetic?) 

Electro-Magnetic Resonator. — (See Res- 
onator, Electro- Magnetic?) 

Electro-Magnetic Shunt. — (See Shunt, 
Electro-Magnetic?) 

Electro-Magnetic Solenoid. — (See Sole- 
noid, Electro-Magnetic.) 

Electro-Magnetic Strain. — (See Strain, 
Electro- Magnetic?) 

Electro-Magnetic Stress. — (See Stress, 
Electro-Magnetic?) 

Electro-Magnetic Theory of Light, Max- 
ell's (See Light, Maxwell's Elec- 
tro-Magnetic Theory of?) 

Electro-Magnetic Vibrator.— (See Vi- 
brator, Electro-Magnetic?) 

Electro-Magnetic Voltmeter.— (See Volt- 
meter, Electro-Magnetic?) 



lie.] 



205 



[Ele. 



Electro-Magnetic Units.— (See Units, 
Electro-Magnetic?) 

Electro-Magnetics. — (See Magnetics, 
Electro?) 

Electro-Massage. — (See Massage, Elec- 
tro?) 

Electro-Mechanical Alarm. — (See Alarm, 
Electro-Mechanical.) 

Electro-Mechanical Gong. — (See Gong, 
Electro-Mechanical^) 

Electro-Metallurgical Crystalline De- 
posit. — (See Deposit, Crystalline, Electro- 
Metallurgical?) 

Electro-Metallurgical Galvanization.— 

(See Galvatiization, Electro- Metallurgical?) 

Electro-Metallurgical Nodular Deposit. 

— (See Deposit, Electro - Metallurgical 
Nodular?) 

Electro - Metallurgical Reguline De- 
posit. — (See Deposit, Electro-Metallurgical 
Reguline?) 

Electro-Metallurgical Sandy Deposit. — 

(See Deposit, Electro-Metallurgical Sandy?) 

Electro-Metallurgy.— (See Metallurgy, 
Electro?) 

Electrometer. — An apparatus for measur- 
ing differences of potential. 

Electrometers operate, in general, by means 
of the attraction or repulsion of charged conduc- 
tors on a suitably suspended needle or disc. As 
no current is required to flow through the appa- 
ratus electrometers are especially adapted to many 
cases where voltmeters could not be so readily 
used. 

Electrometer, Absolute An elec- 
trometer the dimensions of which are such 
that the value of the electromotive force can 
be directly determined from the amount of 
the deflection of the needle. 

A form of attracted-disc electrometer. 
(See Electrometer, Attracted-Disc) 

Electrometer, Attracted-Disc A 

form of electrometer devised by Sir William 



Thomson, in which the force is measured by 
the attraction between the two discs. 

Thomson's Attracted-Disc Electrometer is 
shown in Fig. 230. It consists of a plate C, sus- 
pended from the longer end of a lever 1, within the 
fixed guard plate, or guard ring B, immediately 
above a second plate A, supported on an insulated 
stand, and capable of a measurable approach 




Fig. 230. A.tracted-Disc Electrometer. 

towards C, or a movement away from it. The 
plate, C, is placed in contact with B, by means of 
a thin wire. By means of this connection the 
distribution of the charge over the plate, C, is 
uniform. The electrostatic attraction is meas- 
ured by the attraction of the fixed disc, A, on the 
movable disc, C, connected respectively to the two 
bodies whose difference of potential is to be 
measured. One of these may be the earth. The 
fulcrum of the lever 1, is formed of an aluminium 
wire, the torsion of which is used to measure the 
force of the attraction; or, it may be measured 
directly by the counterpoise weight Q. 

This instrument is sometimes called an absolute 
electrometer, because, knowing the dimensions of 
the apparatus, the value of the difference of poten- 
tial can be directly determined from the amount 
of the motion observed. 

Electrometer, Capillary An elec- 
trometer in which a difference of potential is 




Fig. 231. Capillary Electrometer. 

measured by the movement of a drop of 
sulphuric acid in a tube filled with mercury. 



Ele.] 



206 



[Ele. 



A form of capillary electrometer is shown in 
Fig. 231, in which a horizontal glass tube with 
a drop of acid at B, has its ends connected with 
two vessels M and N, filled with mercury. If 
a current be passed through the tube, a move- 
ment of the drop towards the negative pole 
will be observed. Where the electromotive 
force does not exceed one volt, the amount of 
the movement is proportional to the electro- 
motive force. 

Electrometer, Quadrant An elec- 
trometer in which an electrostatic charge is 
measured by the attractive and repulsive 
force of four plates or quadrants, on a light 
needle of aluminium suspended within them. 

The sectors or quadrants are of brass, and are 
so shaped as to form a hollow cylindrical box 
when placed together. The four sectors, or quad- 
rants, are insulated from one another, but the 
opposite ones are connected by a conducting wire, 
as shown in Fig. t 

232. A light needle 
of aluminium, u, 
maintained at some 
constant potential, 
by connection with 
the inner coating 
of a Ley den jar, is 
suspended, gener- 
ally by two par- 
allel silk threads, 
so as to freely swing inside the hollow box. This 
needle, when at rest, is in the position shown by 
the dotted lines, with its axis of symmetry exactly 
under one of the slots or spaces between two 
opposite sectors. (See Suspension, Bi- Filar.) 

The quadrant electrometer, shown in Fig. 233, 
has one of its quadrants removed so as to show 
the suspended aluminium needle. 

A similar form of instrument is shown in Fig. 
234, with all the quadrants in place, and the 
whole instrument covered by a glass shade. 

To use the quadrant electrometer the pairs of 
sectors are connected with the two bodies whose 
difference of potential is to be measured, and the 
deflection of the needle observed, generally 
through a telescope, by means of a spot of light 
reflected from a mirror attached to the upper part 
of the needle. 

Sometimes the segments are made in the shape 
of a cylinder, and the needle in the shape of a 
suspended rectangle. 



Electrometer, Registering An elec- 
trometer, the deviations of the needle of. 
which are automatically registered. 




Fig. 232. Quadrant Elec- 
trometer. 




Fig. 233. Quadrant Electrometer, Showing Suspended 

Needle. 

The registration of this class of electrometer is 
obtained by means of photography. The spot of 




Fig. 234. Quadrant Electrometer. 

light, reflected from the mirror of the electrometer, 
falls on a fillet of sensitized paper, moved by 
clockwork. 



Ele.J 



20 7 



[Ele. 



Electromotive Arrangement or Device. 

— (See Arrangement or Device, Electromo- 
tive?) 

Electromotive Difference of Potential. — 
(See Potential, Difference of Electromotive?) 

Electromotive Force. — (See Force, Elec- 
tromotive.) 

Electromotive Force, Average (See 

Force, Electromotive, Average or Mean.) 

Electromotive Force, Back or Counter 
(See Force, Electromotive. Back) 

Electromotive Force, Direct (See 

Force, Electromotive, Direct?) 

Electromotive Force, Inductive 

(See Force, Electromotive, Inductive?) 

Electromotive Force, Secondary-Im- 
pressed — (See Force. Electromotive \ 

Secondary-Impressed.) 

Electromotive Force, Simple-Periodic 
— (See Force, Electromotive, Simple- 
Periodic?) 

Electromotive Force, Transverse 

(See Force, Electromotive. Transverse.) 

Electromotive Impulse. — (See Impulse, 
Electro?notive.) 

Electro-Motograph. — (See Motograph, 
Electro?) 

Electro-Muscular. — (See Muscular, Elec- 
tro?) 

Electro-Muscular Excitation. — (See Ex- 
citation, Electro-Muscular?) 

Electroneerosic— Pertaining to capital 
punishment by means of electricity. 

Electronecrosis.— A word proposed for 
capital punishment by means of electricity. 

Electro-Negative Ions. — (See Ions, Elec- 
tro-Negative?) 

Electronegatives. — The atoms or radicals 
that appear at the anode or positive terminal 
during electrolysis. 

The anions. (See Electrolysis. Anion?) 

Electro-Nervous Excitability. — (See Ex- 
citability, Electro-Nervous?) 

Electro- Nickeling. — (See Nickeling, 
Electro?) 

Electro-Optics.— (See Optics, Electro?) 



Electrophanic. — Pertaining to capital pun- 
ishment by means of electricity. 

Electrophanical. — Pertaining to capital 
punishment by means of electricity. 

Electrophanize.— To inflict capital pun- 
ishment by means of electricity. 

Electrophany. — Capital punishment by 
means of electricity. 

The word electrophany would appear to be far 
preferable to the word electrocution, since it is in 
accordance with etymological usage, while elec- 
trocution is not. 

Electrophila. — A devotee of electricity. 

Electrophobia. — A word proposed for fear 
of electricity. 

Electrophoric. — Pertaining to an electro- 
phorus. (See Electrophorus?) 

Electrophorus. — An apparatus for the 
production of electricity 
by electrostatic induc- 
tion. (See Induction, 
Electrostatic?) 

A disc of vulcanite, or 
hard rubber B, contained 
in a metallic form, is rub- 
bed briskly by a piece of 
cat's skin and the insu- 
lated metallic disc, A, is Fig. 235. Electrophorus, 
placed on the centre of the Charging. 

vulcanite disc, as shown in Fig. 235. 

The negative charge produced in B, by fric- 
tion, produces by induction a positive charge on 
the part of A, nearest it, 
and a negative charge 
on the part furthest from 
it. 

In this condition, if 
the disc be raised from 
the plate by means of its 
insulating handle, as 
shown in Fig. 256, no 
electrical effects will be 
noticed, since the two op- 
posite and equal charges 
unite and neutralize each &£> *J 6 « Electrophorus, 
other. If, however, the Discharging. 

disc A, be first touched by the finger, and then 
raised from the disc B, it will be found to be pos- 
itively charged. 





Ele.] 



208 



[Ele. 



E 1 e c t r o-Physiology. — (See Physiology, 
Electro?) 

Electropic Medium. — (See Medium, Elec- 
tropic) 

Electro-Plating 1 . — (See Plating, Electro) 

Electro-Plating Bath. — (See Bath, Elec- 
tro-Plating.) 

Electro-Pneumatic Signals. — (See Sig- 
nals, Electro-Pneumatic.) 

Electro-Pneumatic Thermostat. — (See 
Thermostat, Electro-Pneumatic.) 

Electropoion Liquid. — (See Liquid, Elec- 
tropoion) 

Electro-Positiye Ions. — (See Ions, Elec- 
tro-Positive.) 

Electropositives. — The atoms or radicals 
that appear at the kathode or negative termi- 
nal of any source during electrolysis. 

Thekathions. (Sec Electrolysis. Kathion) 

E 1 e c t r o-Prognosis. — (See Prognosis, 
Electric.) 

Electro-Puncture. — (See Puncture, Elec- 
tro) 

Electro-Receptive Devices. — (See Device, 
Electro-Receptive) 

Electro-Receptive Devices, Multiple-Arc- 
Connected (See Devices, Electro- 
Receptive, Multiple-Arc-Connected) 

Electro-Receptive Devices, Multiple-Se- 
ries-Connected (See Devices, Elec- 
tro-Receptive, Multiple-Series-Connected) 

Electro-Receptive Devices, Series-Con- 
nected (See Devices, Electro-Recep- 
tive, Series-Connected) 

Electro-Receptive Devices, Series-Mul- 
tiple-Connected (See Devices, Elec- 
tro-Receptive, Series-Multiple-Connected) 

Electroscope. — An apparatus for showing 
the presence of an electric charge, or for de- 
termining its sign, whether positive or nega- 
tive, but not for measuring its amount or 
value. 

In the gold-leaf electroscope, two gold leaves, 
n, n, Fig. 239, suspended near each other, show 
by their repulsion the presence of an electric 
charge. Two pith balls may be used for the same 
purpose. 



The pith balls B, B, shown in Fig. 237, form 
a simple electroscope. If repelled by a charge, 
when approached by a similar charge in S, they 
will at once be still further repelled, as shown by 
the dotted lines. 

To use an electroscope for determining the sign of 




Fig- 237. Pith Ball Electroscope. 

an unknown charge, the gold leaves or pith balls are 
first slightly repelled by a charge of known name, 
as, for example, positive, applied to the knob C, 
Fig. 239. They are then charged by the electrified 
body whose charge is to be determined. If they 
are further repelled, its charge is positive. If 
they are first attracted and afterwarJs repelled, 
its charge is negative. 

Two posts B, Fig. 239, connected with the 
earth, increase the amount of divergence by in- 
duction. 



Electroscope, Condensing,Tolta's 



An electroscope employed for the detection 
of feeble charges, the leaves of which are 
charged by means of a condenser. 

The condensing electroscope, Fig. 
formed of two metallic 
plates, placed at the 
top of the instrument, 
and separated by a 
suitable dielectric. 
The upper plate, P, is 
removable by means 
of the insulated han- 
dle, G. 

To employ the elec 
troscope, as for exam- 
ple, to detect the free 
charge in an unequal- Figt 2 3 s. Condensing Elec 
ly heated crystal of troscope. 

tourmaline, the crystal is touched to the lower 
plate, while the upper plate is connected to the 
ground by the finger. On the subsequent re- 
moval of the upper plate an enormous decrease 




Ele.J 



209 



[Ele. 




Fig. 23Q. Gold- Leaf 
Electroscope. 



ensues in the capacity of the condenser, and the 
charge now raises the potential of the lower 
plate, and causes , a marked divergence of the 
leaves L, L. (See Electricity, Fyro.) 

Electroscope, Gold-Leaf An elec- 
troscope in which two leaves of gold are used 
to detect the presence of an electric charge, 
or to determine its character whether positive 
or negative. 

When a charge is imparted to the knob C, Fig. 
239, the gold leaves n, n, diverge. This will oc- 
cur whether the charge be 
positive or negative. 

To determine the char- 
acter of an unknown 
charge, the leaves are first 
caused to diverge by means 
of a known positive or neg- 
ative charge. The un- 
known charge is then given 
to the leaves. If they di- 
verge still further, then the charge is of the same 
name as that originally possessed by the leaves. 
If, however, they first move to- 
gether and are afterwards re- 
pelled, the charge is of the 
opposite name. 

Electroscope, Pith - Ball 

— An electroscope 

which shows the presence of 
a charge by the repulsion of 
two similarly charged pith 
balls. (See Electroscope?) 

Any two pith balls, suspend- 
ed by conducting threads, but 
insulated from the earth, will 
serve as an electroscope. 

Electroscope, Quadrant, 
Henley's An electro- 
scope sometimes employed 
to indicate large charges of 
electricity. 

A pith ball placed on a light 
arm A, of straw or other simi- 
lar material, Fig. 240, is pivoted 
at the centre of a graduated 
circle B. The arm, C, is at- Fig. 240. Henley's 
tached by means of the screw Electroscope. 
to the prime conductor of an electric machine. 
The s : milar charge imparted to A, by contact 





with C, causes a repulsion which may be meas- 
ured on the graduated arc. 

This instrument approaches the electrometer in 
the character of its operation, since by its means, 
approximately correct measurements may be made 
of the value of the repulsion. It should not, how- 
ever, be confounded with the quadrant electroin- 
eter. (See Electrometer ', Quadrant.) 

Electroscopieally. — By means of the elec- 
troscope. (See Electroscope?) 

Electroscopy. — The art of determining the 
kind of charge a body possesses, by means 
of an electroscope. 

Electro - Sensibility. — (See Se?isibility, 
Electro?) 

Electro-Silvering. — (See Silvering, Elec- 
tro.) 

Electro-Smelting. — (See Smelting, Elec- 
tro.) 

Electrostatic Attraction. — (See Attrac- 
tion, Electrostatic?) 

Electrostatic Capacity.— (See Capacity, 
Electrostatic?) 

Electrostatic Circuit. — (See Circuit, 
Electrostatic?) 

Electrostatic Field. — (See Field, Electro- 
static?) 

Electrostatic Induction. — (See Induction, 
Electrostatic?) 

Electrostatic Induction Machine. — (See 
Machine, Electrostatic Induction.) 

Electrostatic Leakage. — (See Leakage, 
Electrostatic?) 

Electrostatic Lines of Force. — (See Force, 
Electrostatic, Lines of.) 

Electrostatic Repulsion. — (See Repulsion, 
Electrostatic?) 

Electrostatic Screening.— (See Screening, 
Electrostatic?) 

Electrostatic Stress. — (See Stress, Elec- 
trostatic?) 

Electrostatic Tnits. — (See Units, Electro- 
static?) 

Electrostatics. — That branch of electric 
science which treats of the phenomena and 
measurement of electric charges. 



Ele.] 



210 



[Ele. 



The principles of electrostatics are embraced 
in the following laws, viz.: 

(i.) Charges of like name, i. e., either positive 
or negative, repel each other. Charges of unlike 
name attract each other. 

(2.) The forces of attraction or repulsion be- 
tween two charged bodies are directly propor- 
tional to the product of the quantities of elec- 
tricity possessed by the bodies and inversely 
proportional to the square of the distance be- 
tween them. 

These laws can be demonstrated by the use of 
Coulomb's torsion balance. (See Balance, Tor- 
sion.) 

Calling q, and q 1 , the quantities of electricity 
possessed by the two bodies, and r, the distance 
between them, then, if f, is the force exerted by 
their mutual action, 

f qq 1 

J r 2 

Electro-Technics.— (See Technics, Elec- 
tro^ 

Electrothanasing\— Producing death by 
electricity. 

Electrothanasis.— A word proposed for 
death by electricity. 

The death referred to here is death other than 
that caused by capital punishment. 

Electrothanasise.— To produce death by 
electricity. 

The death here referred to is other than that 
caused by capital punishment. 

Electrotlianatose. — To cause death by 
electricity. 

Electrothanatosic. — Pertaining to capital 
punishment by means of electricity. 

Electrothanatosing.— Causing death by 
electricity. 

Electrothanatosis. — A word proposed for 
death by electricity. 

The death here referred to is death other than 
that caused by capital punishment. 

Electro-Therapeutic Bath.— (See Bath, 
Electro- Therapeutic?) 

Electro-Therapeutic Breeze. — (See 
Breeze, Electro- Therapeutic?) 



Electro-Therapeutic Diffusion of Cur- 
rent. — (See Current, Diffusion of, Electro- 
Therapeutic^) 

Electro-Therapeutic Dosage.— (S e e 
Dosage, Electro- Therapeutical?) 

Electro-Therapeutic Electrode.— (See 

Electrode, Electro- Therapeutic?) 

Electro-Therapeutic Electrodes.— (See 
Electrode, Electro- Therapeutic?) 

Electro-Therapeutic Galvanization. — 

(See Galvanization, Electro- Therapeutical?) 

Electro-Therapeutic Head-Breeze. — 

(See Breeze, Head, Electro- Therapeutic?) 

Electro-Therapeutics. — (See Therapeu- 
tics, Electro?) 

Electro-Therapeutist. — (See Therapeu- 
tist, Electro?) 

Electro-Therapy. — (See Therapy, Elec- 
tro.) 

Electro-Thermal Meter.— (See Meter, 
Electro- Thermal.) 

Electro-Tinning. — (See Tinning, Elec- 
tro?) 

Electrotisic. — Pertaining to capital pun- 
ishment by means of electricity. 

Electrotising. — Producing capital punish- 
ment by means of electricity. 

Electrotisis. — A word proposed for capi- 
tal punishment by means of electricity. 

Electrotonic Current.— (See Current, 
Electrotonic.) 

Electrotonic Effect.— (See Effect, Electro- 
tonic.) 

Electrotonic Excitability. — (See Excita- 
bility, Electrotonic?) 

Electrotonic State.— (See State, Electro- 
tonic) 

Electrotonus.— A condition of altered 
functional activity which occurs in a nerve 
when subjected to the action of an electric 
current. 



Ele.] 



211 



[Ele. 



The electrotonic state is produced by the 
passage through a nerve of a constant current 
called the polarizing current. 

Electrotonus is attended by the modification of 
the nerve in the following respects, viz. : 

(i.) In its electromotive force. 

(2.) In its excitability. 

The passage of the constant current produces 
a change in the electromotive force of that part of 
the nerve traversed by the current. 

This alteration in muscular excitability may 
consist in either an increased or a decreased func- 
tional activity. The decreased functional activity 
occurs in the neighborhood of the anode, or the 
positive terminal, and is called the anelectrotonic 
state. The increased functional activity occurs in 
the neighborhood of the kathode, or the negative 
terminal, and is called the kathelectrotonic state. 
(See Anelectrotonns. Kathelectrotonns .) 

This altered functional activity affects not only 
the intra polar parts of the nerve, or that part 
between the electrodes, but also the extra-polar 
portions, or, in other words, the remainder of the 
.nerve. 

The electrotonic state is characterized by two 
varieties, viz. : those in which the electromotive 
force of the nerve is decreased, and those in which 
the electromotive force of the nerve is increased. 
These varieties of electrotonus are called respec- 
tively the negative and positive phase of electro- 
tonus. (See Electrotonus, Negative Phase of. 
Electrotonus, Positive Phase of.) 

Electrotonus, Negative Phase of 

A decrease in the electromotive force of a 
nerve effected by sending - a current through 
the nerve in the opposite direction to the 
nerve current. (See Current, Nerve?) 

Electrotonus, Positive Phase of 

An increase in the electromotive force of a 
nerve effected by sending a current through 
the nerve in the same direction as the nerve 
current. 

The increase in the electromotive force not only 
affects the portions of the nerve in the intra-polar 
regions, but in the extra polar regions as well. 

Electrotype. — A type, cast, or impression 
of an object obtained by means of electro- 
metallurgy. (See Metallurgy, Electro. Elec- 
trotyfiing?) 

Electrotyping, or the Electrotype Pro- 



cess Obtaining casts or copies of 

objects by depositing metals in molds by 
the agency of electric currents. 

The molds are made of wax, or other plastic 
substance, rendered conducting by coating it with 
powdered plumbago. 

The mold is connected with the negative 
battery terminal, and placed in a metallic solu- 
tion, generally of copper sulphate, opposite a 
plate of metallic copper, connected with the posi- 
tive battery terminal. As the current passes, the 
metal is deposited on the mold at the kathode, 
and dissolved from the metallic plate at the 
anode, thus producing an exact copy or cast and 
at the same time maintaining constant the strength 
of the bath. 

Electrozemia. — A word proposed for capi- 
tal punishment by means of electricity. 

Electrum. — A name given by the ancients 
to various substances that could be readily 
electrified by friction. 

The term electrum included a number of sub- 
stances, but was applied mainly either to amber 
or to an alloy of gold and silver. 

Element. — Any kind of matter which can- 
not be decomposed into simpler matter. 

Matter that is formed or composed of but 
one kind of atoms. 

Oxygen and hydrogen are elements or varie- 
ties of elementary matter. They cannot be de- 
composed into anything but oxygen or hydrogen. 
Water, on the contrary, is compound matter, 
since it can be decomposed into its constituent 
parts, oxygen and hydrogen. 

There are about seventy well-known elements, 
some of which are very rare, occurring in ex- 
tremely small quantities. 

The evidence of the true elementary condition 
of many of the elements is based, to a great ex- 
tent, on the fact that so far they have resisted all 
efforts made to decompose them into simpler sub- 
stances. We should bear in mind, however, that 
until D ivy's use of the voltaic battery, potash, 
soda, and many other similar compounds were re- 
gaided as true elements. It is not improbable 
that many of the now so-called elements, may 
hereafter be decomposed into simpler constitu- 
ents. 

The following table gives the names, chemical 



Ele.] 212 

symbols, approximate atomic weights and equiva- 
lents of the principal elements : 



[Ele. 



Names ot 
Elements. 



Aluminium . . 
Antimony ... 

Arsenic 

Barium 

Beryllium ... 

Bismuth 

Boron 

Bromine 

Cadmium.. .. 
Caesium. ... 

Calcium 

Carbon 

Cerium 

Chlorine 

Chromium . . 

Cobalt 

Copper 

Didymium... 

Erbium 

Fluorine 

Gallium 

Germanium. . 
Glucinum.... 

Goid 

Hydrogen ... 

lnuium 

Iodine 

Iridium , 

Iron , 

Lanthanum. . 

Lead 

L'thium , 

Magnesium.. . 
Manganese.. 

Mercury . 

Molybdenum. 

Nickel , 

Niobium 

Nitrogen 

Osmium 

Oxygen 

Palladium..., 
Phosphorus. . 

Platinum 

Potassium.... 
Rhodium 
Rubidium 
Ruthenium..., 

Samarium 

Scandium 

Selenium 

Silicon. , 

Silver , 

Sodium , 

Strontium 

Sulphur 

Tantalum 

Tellurium 

Thallium 

Thorium 

Tin 

Titanium 

Tungsten 

Uranium 

Vanadium 
Ytterbium.... 

Yttrium 

Zinc 

Zirconium 



Al. 

bb. 

As. 

Ba. 

Be 

Bi. 

B. 

Br. 

Cd. 

Cs. 

Ca. 

C. 

Ce. 

CI. 

Cr. 

Co 

Cu. 

D 

E. 

F. 

Ga. 

Ge. 

G. 

Au. 

H. 

In. 

I. 

Ir 

Fe. 

L. 

Pb. 

L-. 

Mg. 

Mn. 

Hg. 

Mo. 

Ni. 

Nb. 

N. 

Os. 

O. 

Pd. 

P. 

Pt. 

K. 

R. 

Rb. 

Ru. 

S'n. 

Sc. 

Se. 

bi. 

Ag. 

Na. 

Sr. 

S. 

Ta. 

Te 

Tl. 

Th. 

Sn. 

'Ji. 

W. 

u. 

Va. 

Yb. 

Y. 

Zn. 

Zr. 



o 2'S 



27. 
120. 

74-9 

136.8 

9.1 

207.5 

10.9 

79-8 

in. 8 

132.6 

40. 

12. 

140.4 

35-4 

52- 

58 9 

63.2 

144.6 

165.9 

19. 

68.9 

72.3 

196.2 
1. 

113. 4 
126.6 

192.7 

55-9 

138.5 

206.5 

7- 

*4- 
53-9 

199.7 
95-5 
57-9 
93.8 
14. 

198.5 
16. 

105.7 
3i- 

194.4 

39- 1 
104. 1 

85.3 
104.2 
150.02 

44. 

78.8 

28.2 
107,7 

23. 

87.4 

32. 



233 

117 
48 

183 

238 
5i 

172.8 
89.8 
64.9 
89.4 



Chemical Equivalent.* 



9 _ [compounds 

40 in ous, 24 in ir 
24.9 in ous, 15 in ic 
68.4 

4.6 
69.2 

3-6 

79.8 

55-9 
66.3 



35-4 

26 in ous, 17.3 in ic 

29-5 

31.6 



19. 



196.2 in ous, 65.4 in ic 

37-3 
126.6 

96.4, 64.2, 48.2 
■26 in ous, 18.6 in ic 

I03-3 
7 
12 

2 7 
199.7 in ous, 99.9 inzic 

28 



52 . 9 in ous, 26 . 4 in ic 

6.2 in phosphates 
97.2 in ous, 48 . 6 in ic 
39-. 

52 in ous, 34.7 in ic 
85-3. 
52.1 in o us, 34 . 7 in ic 



7- 
107.7 

23 
43-7 



203 . 7 in ous, 67.9 in ic 

58.9 in ous, 29.4 in ic 
24 in ous, 12 in ic 
91.8 in ous 
119. 2 in ous 
\j.i in ous 



32-5 



* Atomic weight divided by the valency. 



Element, Negative One of the 

substances forming a voltaic couple. (See 
Couple, Voltaic?) 

Element, Negative, of a Toltaic Cell 

— That element or plate of a voltaic cell into* 
which the current passes from the exciting^ 
fluid of the cell. 

The plate that is not acted on by the elec- 
trolyte during the generation of current by 
the celL 

The copper or carbon plate, respectively, 
in a zinc-copper or zinc-carbon couple. 

It must be carefully borne in mind that the 
conductor attached to the negative element of a 
voltaic pile is the positive conductor or electrode 
of the pile, since the current that flows into the 
plate from the liquid or electrolyte must flow out 
of the plate where it projects beyond the liquid. 

Element of Current. — (See Current, Ele- 
ment of.) 

Element of Storage Battery. — (See Bat- 
tery, Storage, Element of.) 

Element, Positive That element or 

plate of a voltaic cell from which the current 
passes into the exciting fluid of the cell. 

The element of a voltaic couple which is 
acted on by the exciting fluid of . the cell.. 
(See Couple, Voltaic) 

Element, Thermo-Electric One of 

the two metals or substances which form a 
thermo-electric couple. (See Couple, Ther- 
mo-Electric) 

Element, Voltaic One of the two 

metals or substances which form a voltaic 
couple. (See Couple, Voltaic) 

Elements, Electrical Classification of 

A classification of the chemical ele- 
ments into two groups or classes according 
to whether they appear at the anode or kathode 
when electrolyzed. 

The chemical elements may be arranged into 
electro-positive and electro-negative according to 
whether, during electrolysis, they appear at the 
negative or positive terminal of the source respec- 
tively. 

The electro-positive elements or radicals are- 
called kathions, and appear at the kathode or 
electro-negative terminal. The electro-negative: 



Ele.J 



213 



[Ene. 



elements are called anions, and appear at the 
anode, or the electro- positive terminal. (See 
Ions.) 

The metals generally are electro-positive; oxy- 
gen, chlorine, iodine, fluorine, etc., are electro- 
negative. 

Elements, Magnetic, of a Place 

The values of the magnetic intensity, the mag- 
netic declination or variation, and the mag- 
netic inclination or dip at any place. 

Elevator Annunciator. — (See Annuncia- 
tor, Elevator :) 

Elevator, Electric An elevator 

operated by electric power. 

Elongated Ring Core. — (See Core, Ring, 
Elongated?) 

Elongation, Magnetic An increase 

in the length of a bar of iron on its magnetiza- 
tion. 

This increase in length is thought to greatly 
strengthen Hughes' theory of magnetism. (See 
Magnetism, Hughes' 1 Theory of.) 

Elongation of Needle. — (See Needle-, Elon- 
gation of.) 

Embosser, Telegraphic An appa- 
ratus for recording a telegraphic message in 
raised or embossed characters. 

Emptied. — A term sometimes applied to a 
completely discharged secondary or storage 
cell. 

It is difficult to determine exactly when a stor- 
age cell is completely emptied or "discharged." 
The cell is generally regarded as discharged 
when its voltage falls below a certain point. 

Endosmose. — The unequal mixing of two 
liquids or gases through an interposed me- 
dium. 

The presence of an electric current affects the 
endosmose. (See Currents, Diaphragm.) 

Endosmose, Electric. — Differences in the 
level of liquids capable of mixing through the 
pores of a diaphragm separating them, pro- 
duced by the flow of an electric current 
through the liquid. 

Wiedemann, who investigated these phenom- 
ena, employed a porous earthenware vessel closed 
at the bottom and terminated at its upper end by 
a glass bell provided with a glass tubulure, to 



which was attached a horizontal arm for the es- 
cape of the liquid raised in the tubulure. The 
battery terminals were attached to platinum elec- 
trodes placed- respectively inside the porous cell, 
and in a vessel of water outside of the porous cell, 
in which the porous cell was placed ; on the passage 
of the current from the outside of the cell to the 
inside the liquid rose in the glass tubulure and ran 
over the horizontal tube into a vessel placed ready 
to receive it. 

Energizing, Electrically Causing 

electricity to produce any effect in an electro- 
receptive device. 

An electro-magnet is energized by the passage 
of a current through its coils. 

Energy. — The power of doing work. 

The amount of work done is measured by the 
product of the force, by the space through which 
the force moves. Thus one pound raised verti- 
cally through ten feet, ten pounds raised through 
one foot, or five pounds raised through two feet, all 
represent the same amount of work; viz., ten foot- 
pounds. 

If a weight of ten pounds be raised through a 
vertical height of one foot, by means of a string 
passing over a pulley, there will have been ex- 
pended an amount of energy represented by the 
work often foot-pounds. If the weight be pre- 
vented in any way from falling, as by securing 
the string to a fixed support, the weight will have 
stored in it an amount of energy equal to ten foot- 
pounds, and if permitted to fall, wilL be capable 
of doing an amount of work which, leaving out air 
resistance and friction, is exactly equal to that 
originally expended in raising it to the position 
from which it fell; viz., ten foot-pounds of work. 

Energy, Actual Energy actually 

employed in doing work as distinguished 
from energy that only possesses the power of 
doing work, but not actually doing such 
work. 

This term is also used in the sense of kinetic 
energy or energy due to motion, but kinetic en- 
ergy is no more actual than potential energy. 

Energy, Atomic Chemical-potential 

energy. (See Energy, Chemical-Potential.) 
Energy, Chemical-Potential The 

potential energy possessed by the elementary 
chemical atoms. (See Energy, Potential.) 
If a weight of one pound be raised vertically 



Ene.] 



214 



[Ene. 



against the earth's attraction, through a distance 
of say ten feet, and placed on a suitable support, 
an amount of energy, equal to the ten foot-pounds 
of work done on the weight, becomes potential. 

In the same manner if the elementary atoms of 
carbon and oxygen, when combined so as to form 
carbonic acid, are raised or separated fi om one 
another sufficiently to decompose the carbonic 
acid and separate the carbon from the oxygen, the 
amount of potential energy the carbon and oxygen 
possess, as a result of having been separated, is 
equal precisely to that originally required to sepa- 
rate them. In this manner each chemical element 
possesses a store of chemical- potential energy 
peculiar to it, and any element with which it may 
subsequently enter into combination. When ele- 
ments combine chemically this potential energy is 
expended in producing heat. 

Energy, Conservation of The in- 
destructibility of energy. 

The total quantity of energy in the universe is 
unalterable. 

The total energy of the universe is not, how- 
ever, available for the production of work useful 
for man. 

When energy disappears in one form it reap- 
pears in some other form. This is called the con- 
servation or indestructibility of energy. The com- 
monest form in which energy reappears is as heat, 
and in this case some of the heat is lost to the 
earth by radiation. This degradation or dissipa- 
tion of energy causes some of the energy of the 
earth to become non-available to man. 

Energy is therefore available and non-available. 
(See Entropy.) 

Energy, Correlation of A term 

sometimes applied to the different phases un- 
der which energy may appear. 

Since energy is indestructible, when it disap- 
pears in one form or phase, it must reappear in 
another form or phase. The correlation of the 
different phases of energy, therefore, necessarily 
follows from the fact that all energy is indestruc- 
tible. 

Energy, Degradation of Such a 

dissipation of energy as to render it non- 
available to man. (See Energy, Conserva- 
tion of. Entropy?) 

Energy, Dissipation of The ex- 
penditure or loss of available energy. 



Energy, Electric —The powei 

which electricity possesses of doing work. 

In the case of a liquid mass at different levels, 
the liquid at the higher level possesses a certain 
amount of potential energy measured by the 
quantity of the liquid at the higher level, an 1 the 
excess of its height over that of the lower level; 
or, by the difference between the two levels. Any 
difference of level will produce a flow of the liquid 
from the higher to the lower level, and during 
the flow of this current of liquid, potential energy 
will be lost, and a certain amount of work will be 
done. 

In the case of electricity, the difference of elec- 
tric level, or potential, between any two points of 
a conductor, causes an electric current to flow 
between these points toward the lower electric 
level, during which electric potential energy is 
lost, and work is accomplished by the electric 
current. (See Potential, Electric.) 

The amount of this electric work is measured by 
the quantity of electricity that flows, multiplied 
by the difference of potential under which it 
flows. (See Joule. Volt -Coulomb.) 

Electric energy, however, is generally meas- 
ured in electric power, or rate of doing electric 
xvork. 

Since an ampere is one coulomb-per-second, if 
we measure the difference of potential in volts, 
the product of the amperes by the volts will give 
the electrical power in volt -amperes, or watts, or 
units of electric power. C E = Watts. (See 
Ampere. Volt. Watt.) 

One horse power equals 550 foot-pounds per 
second. One watt or volt-ampere =: 7 |g of a 
horse-power, or one horse-power equals 746 volt 
amperes or watts, therefore: 

The curre7it in amperes, multiplied by the dif- 
ference of potential in volts, divided by 746, 
equals the rate of doing work in horse-powers. 

Thus, if .7 ampere is required to operate a 
16 candle, no volt, incandescent lamp, it requires 
4.8 watts per candle. 

One Watt = 44.2394 foot-pounds per minute. 

One Watt == .737324 foot-pound per second. 

The Heat Activity, or the heat-per-second 
produced by an electric current, is also propor- 
tional to the product C E, or the watts, for the 
heat is proportional to the square of the current 
in amperes multiplied by the resistance in ohms, 
or C 2 R = the watts. (See Calorimeter, Elec- 
tric.) 



£ne.] 



215 



[Ene. 



By Ohm's Law (See Ohm's Law) 

C = 5- (i), or C R = E (2), 
K 

But the electric power, or the watts, = C E (3). 
If, now, we substitute the value of E, taken 
frcm equation (2) in equation (3) we have 

CE = C X CR = C2 R; 
therefore C 2 R = Watts. 

To determine the heating power of a current 
•in small calories, calling H, the amount of heat 
required to raise 1 gramme of water through i° 
Cent., and C, the current in amperes — 

H = C 2 R X .24. 
Or, for any number of seconds, t, 
H = C 2 R/ X .24. 
(See Calorie.) 

But from Ohm's Law, 

c = | 0, 

and the formula for electric power or the watts 
= C E. (2) By substituting in equation (2) 
and the value of C, in equation (1), 

F F 2 

CE = Ex^^- = Watts. 

That is to say, the electric power in any part of 
a circuit varies directly as the square of the 
electromotive force. 

We, therefore, have three expressions for the 
value of the watt, or the unit of electric power, 
*viz. : 

C E = Watts. (1) 

C 2 R = Watts. (2) 

^= Watts. (3) 

(I.) C E = Watts; or the electric power is pro- 
portional to the product of the quantity of elec- 
tricity ptr -second, that passes, in amperes, and 
the difference of electric potential or level, 
through which it passes, in volts. 

(2.) C 2 R = Watts; or the electric power 
varies directly as the resistance R, when the cur- 
rent is constant, or as the square of the current, 
if the resistance is constant. That is to say, if 
with a given resistance the power of a given 
current has a certain value, and the current 
flowing through this same resistance be doubled, 
the power is four times as great, or is as the 
square of the current. 

E 8 

(3-) tY- = Watts, or the electric power is in- 



versely as the resistance R, when the electro- 
motive force is constant, and is directly propor- 
tional to the square of the electromotive force if 
the resistance is constant. 

A circuit of one ohm resistance will have a 
power of one watt, when under an electromo- 
tive force of one volt, since it would then have 
a current of one ampere flowing through it, and 
CE = i. If, however, the resistance be halved 
or becomes .5 ohm, then two amperes pass, or 
the power equals 2 watts. 

The power varies as the square of the electro- 
motive force in any part of a circuit, when the 
resistance is constant in that part. Thus 2 am- 
peres, and 2 volts, in a circuit of one ohm 
resistance, give a power, C E = 2 X 2 =4 watts. 
If now, R, remaining the same, the electro- 
motive force be raised to 4 volts, then since E, is 
doubled, C, or the amperes, is doubled, and C 

XE = 4X4=i6 watts, or -5- = — = 16. 
K. I 

Energy, Electric, Transmission of 

— The transmission of mechanical energy be- 
tween two distant points connected by an 
electric conductor, by converting the me- 
chanical energy into electrical energy at one 
point, sending the current so produced 
through the conductor, and reconverting the 
electrical into mechanical energy at the other 
point. 

A system for the electric transmission of energy 
embraces: 

(1.) A conducting circuit between the two 
stations. 

(2.) An electric source or battery of electric 
sources or machines at one of the stations, gener- 
ally in the form f a dynamo-electric machine 
or machines, for converting mechanical energy 
into electric energy. 

(3.) Electro-receptive devices, generally electric 
motors, at the other station for reconverting the 
electric into mechanical energy. (See Motor, 
Electric. ) 

Energy, Flow of The flow or trans- 
mission of energy from the medium or die- 
lectric surrounding a conductor which is 
directing a current of electricity on to the 
conductor. * (See Law, Poyntzng's.) 

Energy, Hysteresial, Dissipation of 

— The dissipation of energy by means of 



EneJ 



213 



[Ent. 



hysteresis. (See Energy, Dissipation of. 
Hysteresis?) 

Energy, Kinetic Energy which is 

due to motion as distinguished from potential 
energy, (See Energy, Potential) 

Energy-Meter.— (See Meter, Energy) 

Energy of Position. — (See Position, En~ 
ergy of) 
Energy of Stress. — (See Stress, Energy 

"/■) 

Energy, Potential Stored energy. 

Potency, or capability of doing work. 

Energy possessing the power or potency of 
doing work, but not actually performing such 
work. 

The capacity for doing work possessed by 
a body at rest, arising from its position as 
regards the earth, or from the position of its 
atoms as regards other atoms, with which it 
is capable of combining. 

A pound of coal, if raised vertically one foot, 
possesses, as a mere weight, an amount of energy 
capable of doing an amount of work equal to one 
foot-pound. The atoms of carbon, however, of 
which it is composed, have been raised or sepa- 
rated from those of oxygen, or some other elemen- 
tary substance, and when the coal is burned, or 
the carbon atoms fall towards the oxygen atoms 
(z. e., unite with them), the coal gives up the 
potential energy of its atoms in the form of heat. 

All elementary substances possess in the same 
way atomic or chemical-po 'ential energy, or the 
energy with which they tend to fall together, 
or enter into combination. This energy varies in 
amount in different elements and becomes kinetic, 
as heat, on combination with other elements. (See 
Energy, Chemical- Potential.) 

Energy, Radiant Energy trans- 
ferred to or charged on the universal ether. 

Radiant energy is of three forms, viz.: 
(I.) Obscure radiation, or heat. 
(2.) Luminous radiation, or light. 
(3.) Electro-magnetic radiation. 

Energy, Static A term used to ex- 
press the energy possessed by a body at rest, 
resulting from its position as regards other 
bodies, in contradistinction to kinetic energy 
or the energy possessed by a body whose 



atoms, molecules or masses are in actual 
motion. 

Potential energy. 

The general term for static energy is potential 
energy. (See Energy, Potential.) 

Energy, Storage of —The change 

from any form of kinetic energy, to any form 
of potential energy. (See Energy. Kinetic. 
Energy, Potential) 

Engine, Electro-Magnetic A mo- 
tor whose driving power is electricity. (See 
Motor, Electric) 

Engraving, Acoustic Engraving 

by the human voice. 

In the Phonograph, Graphophone and Gramo- 
phone, a diaphragm, set in vibration by the 
speaker's voice, cuts or engraves a record of it9 
to-and-fro movements on a sheet of tin foil, a 
cylinder of hardened wax, or a specially coated 
plate of mctrd or glass. This record is employed 
in order to reproduce the speech. (See Phonograph. ) 

Engraving, Electric — A method 

for electrically etching or engraving a me- 
tallic plate by covering it with wax, tracing 
the design on the wax so as to expose the 
metal, connecting the metal with the positive 
terminal of a battery, and placing it in a 
bath opposite another plate of metal. 

By the action of electrolysis the metal is dis- 
solved from the exposed portions and deposited 
on the plate connected with the other terminal 
of the battery. (See Electrolysis.) 

In this manner the design is obtained in the 
form of an etching or cutting of the plate. 

By connecting the waxed plate to the negative 
terminal of the electric source, the metal will be 
deposited on the exposed portions of the plate, 
thus producing the design in relief. Unless 
great care is taken, this latter method is not, 
however, apt to produce a sufficiently uniform 
deposit to enable the plate so formed to be used 
for printing from. 

Electric engraving is sometimes called electro- 
etching. 

Entropy. — In thermo-dynamics the non- 
available energy in any system. — {Clausius 
and Mayer) 

In thermo-dynamics, the available energy 
in any system. — ( Tait, Thomson and Max- 
well) 



Ent.] 



217 



[Equ. 



As will be noticed, this term is used in entirely 
different and opposite senses by different scientific 
men. The latter sense is, perhaps, the one most 
generally taken. 

Heat energy is available for doing useful exter- 
nal work only when the source of heat utilized is 
hotter than surrounding bodies, that is, when the 
heat is transferred from a hotter to a colder body. 
When all bodies have acquired the same temper- 
ature, they can do no more external work. In 
the various transformations of energy some of the 
energy is converted into heat, and this heat is 
gradually diffused through the universe and thus 
becomes non-available to man. Therefore, the 
entropy of our earth is decreasing. 

"Entropy, in thermodynamics," says Max- 
well, " is a quantity relating to a body such that 
its increase or diminution implies that heat has 
entered or left the body. The amount of heat 
which enters or leaves the body is measured by the 
product of the increase or diminution of entropy 
into the temperature at which it takes place." 

Entropy, Electric — A term pro- 
posed by Maxwell for use in thermo-elec- 
tric phenomena to include the doctrine of 
entropy in electric science. 

"When an electric current,'' says Maxwell, 
"passes from one metal to another, heat is 
emitted or absorbed at the junction of the metals. 
We should, therefore, suppose that the electric 
entropy has diminished or increased when the 
electricity passes from one metal to the other, the 
electric entropy being different according to the 
nature of the medium in which the electricity is, 
and being affected by its temperature, stress, 
strain, etc." 

Equalizer, Feeder An adjustable 

resistance placed in the circuit of a feeder for 
the purpose of regulating the difference of 
potential at the junction box. 

Equalizer, Magnetic A device for 

equalizing the otherwise unequal force ex- 
erted between a magnet pole and its arma- 
ture at varying distances. 

Since the force of magnetic attraction increases 
rapidly with the decrease of the distance, it fol- 
lows that any force sufficiently great to cause the 
motion of an "armature towards a pole, against the 
force of gravity, will result in the movement of the 
armature to the pole, and that, therefore, no dif- 
ferentiation as to the final result will be produced 



by a powerful current, and a current just strong 
enough to start the action. If, however, the 
armature move against the action of a spring, the 
latter can be so arranged that the force with 
which it opposes the motion of the armature in- 
creases, the nearer the armature is to the pole, 
and in this way the movement of the armature 
can be made proportional to the strength of the 
current energizing the electro-magnet. 

A similar method consists in mechanical devices 
that cause the armature to work with lessened 
mechanical advantage as it approaches the pole. 

Or, the polar surfaces may be so shaped by cut- 
ting, or by the addition of suitable projections, 
as to cause the approach of the armature to be 
attended by a nearly constant force. 

Equator, Geographical An imag- 
inary great circle passing around the earth 
midway between its poles. 

Equator, Magnetic ■ — The magnetic 

parallel or circle on the earth's surface where 
a magnetic needle, suspended so as to be free 
to move in a vertical as well as in a horizontal 
plane, remains horizontal. 

An irregular line passing around the earth 
approximately midway between the earth's 
magnetic poles. (See Dip or Inclination, 
Angle of.) 

Equator of Magnet. — (Set Magnet, Equa- 
tor of.) 

Equatorial. — Pertaining to the equator. 

Eqnatorially. — In the direction of the 
equator. 

Equipotential Surface of a Conductor 
through which a Current is Flowing. — 
(See Surface, Eqnipote7itial, of a Conductor 
through which a Current is Flowing.) 

Equipotential Surface, or Level Surface 
of Escaping Fluid. — (See Surface, Equipo- 
tential, or Level Surface of Escaping Fluid.) 

Equipotential Surfaces,Electrostatic 

— (See Surfaces, Equipotential, Electro- 
static^) 

Equipotential Surfaces, Magnetic 

— (See Su? faces, Equipotential, Magnetic.) 

Equivalence, Electro-Chemical, Law of 
The amount of chemical action pro- 
duced by an electric current, passed through 
various chemical substances, is proportional 
to the chemical equivalent of each substance, 



Equ.] 



218 



[Equ 



that is, to its atomic weight, divided by its 
valency. (See Valency.) 

Thus, the atomic weight of oxygen is sixteen 
times greater than the atomic weight of hydrogen. 
Oxygen is a diad; that is, has twice the combin- 
ing power of hydrogen. The passage of a given 
quantity of electricity will liberate eight times, by 
weight, as much oxygen as hydrogen; or, to put 
it in another way, the passage of a given quan- 
tity of electricity will liberate two atoms of 
hydrogen for every atom of oxygen. 

The atomic weight of chlorine is 35.4. The 
passage of a given amount of electricity will 
liberate a weight of chlorine 35.4 greater than the 
weight of hydrogen; or, for every atom of 
chlorine it will liberate one atom of hydrogen. 
Here the passage of a given amount of electricity 
liberates one atom of the monad element hydrogen 
for every atom of the monad element chlorine. 

The atomic weight of gold is 196.2, and its 

atomicity or valency is 3. The passage of a 

196.2 
given amount of electricity will liberate — -— = 

65.4 in ic compounds as great a weight of the 
triad element gold as of hydrogen ; or, will liberate 
them in the proportion of one atom of gold for 
every three atoms of hydrogen. 

Generalizing, it appears, therefore, that the 
passage of the same quantity of electricity through 
an electrolyte liberates the same number of atoms 
of a monad element, no matter what their nature 
may be. It liberates one-half as many of the diad 
atoms as it does of the monads, and one-third as 
many of the triad atoms as of the monads. 

Professor Lodge points out, that assuming the 
-""truth of the theory that a current of electricity 
flows in an electrolyte by means of a true electric 
convection, each atom carrying an electric 
charge, then it would seem that every monad 
atom carries an equal charge of electricity, 
whether it be an atom of hydrogen, chlorine, 
potassium, silver, or mercury. That each diad 
element carries twice as much, and that each 
triad element carries three times as much. 

In general, the number of atoms liberated by a 
given current of electricity is equal to the num- 
ber of atoms of hydrogen, divided by the valency 
of the atom. ' ' The electric charge, ' ' says Lodge, 
•'belonging to each atom of matter, is a simple 
multiple of a definite quantity of electricity, which 
quantity is an absolute constant, quite independent 
of the nature of the particular substance to which 
the atom belongs." 



The specific charge thus hypothetically given to- 
each atom of matter is believed never to be lost. 

Atoms capable of entering into combination are 
supposed to be oppositely charged, and chemical 
affinity is, according to this supposition, believed 
to be the result of th e mutual attractions of opposite 
electric charges naturally and originally pos- 
sessed by the atoms of matter. 

Lodge points out the following results which 
naturally flow from the hypothesis that the atoms 
of matter possess definite positive and negative 
charges of electricity, viz. : 

(1.) That the amount of electricity possessed 
by each monad atom is exceedingly small, being 
about the hundred thousand millionth part of 
the ordinary electrostatic unit, or less than the 
hundred trillionth of a coulomb. 

(2.) The charge being small, the potential is 
necessarily low. 

Probably something between one and three 
volts is a high difference of potential between two 
oppositely charged atoms. 

(3.) The nearness of the attracting atoms, how- 
ever, can cause a very strong electrostatic attrac- 
tion between them. 

(4. ) That chemical affinity, or atomic attraction, 
is caused by the presence of these electric charges. 

(5.) That the electrical force between two 
atoms at any distance is ten thousand million 
billion billion times greater than their gravitation 
attraction at the same distance, or, the force has 
an intensity per unit of mass capable of producing 
an acceleration, nearly one trillion times greater 
than that of gravity at the earth's surface. 

Equivalent, Chemical The quo- 
tient obtained by dividing the atomic weight 
of any elementary substance by its atomicity. 
(See Weight, Atomic. Atomicity.) 

The ratio between the quantity of an ele- 
ment and the quantity of hydrogen it is 
capable of replacing. 

That quantity of an elementary substance 
that is capable of combining with or replac- 
ing one atom of hydrogen. 

The chemical equivalent has a different value 
from the 'atomic weight whenever the valency 
is greater than unity. Thus the atomic weight 
of gold is 196.2, but since in ic compounds one 
atom of gold is capable of combining with three 
atoms of hydrogen, the weight of the gold equiva- 
lent to that of one atom of hydrogen is one-third 
of 196.2, or 65.4. 



Eqn. 



219 



[Esc. 



Equivalent Conductivity.— (See Conduc- 
tivity, Equivalent^ 
Equivalent, Electro-Chemical A 

number representing the weight in grammes 
of an elementary substance liberated during 
electrolysis by the passage of one coulomb of 
electricity. (See Electrolysis. Coulomb.) 

The chemical equivalent of a substance 
multiplied by the electro- chemical equivalent 
of hydrogen. 

The electro-chemical equivalent is, therefore, 
found by multiplying the electro-chemical equiva- 
lent of hydrogen by the chemical equivalent of 
the element. 

It may be determined experimentally that one 
coulomb of electricity, expended electrolytically, 
will liberate .0000105 gramme of hydrogen. 
Therefore a current of one ampere •, or one coulomb - 
per -second, will liberate .0000105 gramme of hy- 
drogen per second. The number .0000105 is the 
electro-chemical equivalent of hydrogen. 

In the same manner the electro-chemical equiva- 
lents of the other elements are obtained by multi- 
plying the electro-chemical equivalent of hydrogen 
by the chemical equivalent of the substance. 

Thus, the chemical equivalent of potassium is 
39.1, therefore its electro-chemical equivalent is 
39.1 X .0000105 = .00041055. By multiplying 
the strength of the current that passes by the 
electro-chemical equivalent of any substance we 
obtain the weight of that substance liberated by 
electrolysis. (See Equivalence, Electro-Chemical, 
Law of.) 

To determine the electro-chemical equivalent 
of the other elements see table of chemical equiva- 
lents on page 212. 

Equivalent, Joule's — The mechan- 
ical equivalent of heat. (See Heat, Mechan- 
ical Equivaleiit of.) 

Equivalent of Heat, 3Iechauicai 

(See Heat, Mechanical Equivalent of.) 

Equivalent Eesistance.— (See Resistance, 
Equivale?it.) 

Equivolt— A term proposed by J. T. 
Sprague for the unit of electrical energy, ap- 
plied especially to chemical decomposition. 

Sprague defines an equivolt as follows : ' ' The 
mechanical energy of one volt electromotive force 
exerted under unit conditions through one equiva- 
lent of chemical action in grains." 



This term has not been generally accepted. 
(See Volt -Coulomb. Joule.) 

Erb's Standard Size of Electrodes.— (See 

Electrodes, Erb's Standard Size of.) 

Erg". — The unit of work, or the work done 
when unit force is overcome through unit 
distance. 

The work accomplished when a body is 
moved through a distance of one centimetre 
with the force of one dyne. (See Dyne.) 
A dyne centimetre. 

The work done when a weight of one gramme 
is raised against gravity through a vertical height 
of one centimetre is equal to 981 ergs, because 
the weight of one gramme is 1 X 981 dynes, or 
981 ergs. 

The following values for the erg, the unit of 
work, and the dyne, the unit of force, are taken 
from Hering: 

1 erg = 1 dyne centimetre. 
I erg = 0.0000001 joule. 
981 ergs == 1 gramme centimetre. 
1,937.5 ergs = I foot grain. 
13,562,600 ergs = 1 foot-pound. 

1 dyne == 1. 0194 milligrammes. 
I dyne =0.015731 grain. 
I dyne = 0.0010194 grammes. 
1 dyne == 0.00003596 ounce avoirdupois, 
63.568 dynes = 1 grain. 
981 dynes = 1 gramme. 

Ergmeter. — An apparatus for measuring 
the work of an electric current in ergs. 

Erg-ten. — A term proposed for ten million 
ergs or 1 X 10 10 = 10,000,000,000. 

In representing large numbers containing many 
ciphers the following plan is generally adopted for 
representing the number of ciphers that are to be 
added to a given number. Thus, suppose it is 
desired to represent the number 3,800,000,000. 
When written 38 X 10 8 it indicates that 38 is to 
be multiplied by io 8 or 100,000,000, or, in other 
words, that 38 is to be followed by 8 ciphers, 
thus 3,800,000,000. 

A negative exponent, as 3 X i°~ 8 represents 
the corresponding decimal thus, .00000003. 

I erg X io 10 , or 10,000,000,000 is called an 
erg ten. 1 X i° 6 = an erg six. These terms 
are not in general use. Ten meg-ergs is a pref- 
erable phrase to an erg-ten. (See Meg-erg. ) 

Escape, Electric A term some- 



Esc] 



220 



[Eva. 



times employed to indicate the loss of charge 
on an insulated conductor. (See Leakage, 
Electric?) 

Escaping" Fluid, Flow-Lines of 

(See Flow-Lines of Escaping Fluid?) 

Escaping Fluid, Stream-Lines of 

* (See Stream-Lines of Escaping Fluid.) 

Essential Resistance. — (See Resistance, 
Essential?) 

Etching, Electro — 



-A term some- 



times employed instead of electro-engraving. 
(See Engraving, Electric?) 

Etching", Galvanic Electro-En- 
graving. (See Engraving, Electric?) 

Ether. — The tenuous, highly elastic fluid 
that is assumed to fill all space, and by vibra- 
tions or waves in which light and heat are 
transmitted. 

Although the existence of the ether is assumed 
in order to explain certain phenomena, its actual 
existence is very generally credited by scientific 
men, and, in reality, proofs are not wanting to 
fairly establish such existence. 

Light and heat are believed to be due to trans- 
verse vibrations in the ether. Magnetism appears 
to be due to whirls or whirlpoo s, and an elec- 
tric current is believed by some to be due to 
pulses of waves of ether set in motion by differ- 
ences in the ether pressures. 

It is not correct to regard the luminiferous 
ether as possessing no weight, or as being im- 
ponderable. Maxwell estimates its density as 

^k- that of water. It 

I , ooo, ooo, ooo, ooo, ooo, ooo, ooo 

is very readily moved or set into vibration, its 

rigidity being estimated at about 

° J ° 1,000,000,000 

that of steel. 

According to the speculations of some physi- 
cists the ether is not discontinuous or granular, 
but it is similar to what might be regarded as an 
almost impalpable jelly. 

Ethereal. — Pertaining to the universal 
ether. 

Eudiometer. — A voltameter in which sep- 
arate graduated vessels are provided for the 
reception and measurement of the gaseous 
products evolved during electrolysis. (See 
Volta?neter?) 




In all cases electrodes for eudiometers must be 
used which do not enter into combination with the 
evolved gaseous products. In the case of oxygen 
and hydrogen, platinum is generally used. 

A form of eudiometer is shown in Fig. 241. 
Two separate glass ves- 
sels, provided at the top 
with stop cocks, and 
open at their lower 
ends, rest in a vessel of 
water A, over platinum 
electrodes, connected 
electrically with binding 
posts K, K. Both ves- 
sels are filled with water 
slightly acidulated with 
sulphuric acid, and, 
when connected with 
a battery of sufficient 
electromotive force (not 
less than 1.45 volts), 
electrolysis takes place, Fig, 24 r. Eudiometer. 
and hydrogen gas collects in the vessel over 
the platinum electrode connected with the neg- 
ative battery terminal, and oxygen in the vessel 
over the electrode connected with the positive 
battery terminal. The volume of the hydrogen 
is approximately twice as great as that of the 
oxygen. (See Water, Electrolysis of.) 

The proportion is not exactly 2 to 1, because, 

(1.) Some of the hydrogen is occluded or ab- 
sorbed by the platinum electrode. 

(2.) Some of the oxygen is given off as tri- 
atomic oxygen, or ozone, which is denser and 
occupies less space than free atomic oxygen. 

Eudiometric— Pertaining to the eudiom- 
eter. (See Eudiometer?) 

Eudiometrically. — By means of the eudi- 
ometer. 

Evaporation.— The change from the liquid 
to the vaporous state. 

Wet clothes exposed to the air are dried by the 
evaporation of the water. 

Evaporation is greater: 

(1.) The more extended the surfaces exposed. 

(2.) The higher the temperature of the air. 

(3.) The dryer the air, or the smaller the 
quantity of vapor it contains already. 

(4.) The stronger the wind. 

(5.) The smaller the barometric pressure. 

Evaporation, Electric The forma- 



Hva.] 



221 



[Exc. 



lion of vapors at the surfaces of substances 
by the influence of negative electrification 

The term electric evaporation was proposed by 
Crookes for the formation of metallic vapors of 
such substances as metallic platinum, exposed in 
high vacua t) the effects of negative electrifica- 
tion. He shows that under these circumstances 
-the surface molecules of the platinum lose their 
power of cohering and fly off into the space 
around them, i. e , suffer true evaporation. This 
action takes place under atmospheric pressures, 
but. like ordinary evaporation, is greatly facili- 
tated by the presence of a high vacuum. 

True electric evaporation takes place with 
liquids as well as with solids. In an experiment 
with water, the influence of the kind of the elec- 
trification was clearly shown. A vessel of water 




Fig. 242. Electrical Evaporation. 

exposed to the air was first positively electrified, 
but after an exposure of i| hours only a trifling 
evaporation was noticeable. The water was 
then negatively electrified, and at the end of ii 
hours had lost yoV o P ar ^ °^ * ts we ight more than 
did the positively charged water. 

Professor Crookes experimented with cadmium, 
and, in order to show that electric evaporation is 
different from evaporation produced by the agency 
of heat, tried the following, viz.: A high vacuum 
U-tube, shaped as shown in Fig 242, was pro- 




Fig 243. Electrical Evaporation. 

vided with platinum poles sealed in the glass at 
A and B. Two pieces of cadmium, C and D, 
were placed in the tube in the position shown, 
and the tube uniformly heated by means of a gas- 
burner and air bath, and maintained at a constant 
temperature. The current was then passed for 
about an hour, B. being made the negative pole. 



No metal was deposited in the neighborhood of 
the positive pole, the portions ot the tube sur- 
rounding the positive pole being quite clean, 
while the corresponding portions of the other limb 
of the tube were thickly coated, as shown by the 
shading m the drawmg- 

In another experiment, in which the tempera- 
ture was kept lower than in the preceding, viz., 
just below the melting point of the cadmium, 
after the current had passed for an hour, the limb 
of the tube through which the current had passed 
had received a thick coating, while the other was 
nearly free from coating, as shown in Fig. 243. 
Here the increase in the amplitude of t' e mole- 
cular oscillation under the influence of the elec- 
tricity is manifest. 

Evaporation, Electrification by — 



An increase in the difference of potential ex- 
isting in a mass of vapor attending its sudden 
condensation. 

The free electricity of the atmosphere is be- 
lieved by some to be due to the condensation of 
the vapor of the air that results in rain, hail, 
clouds, etc. It is probable, however, that the 
true effect of condensation is mainly limited to 
the increase of a feeble electrification already 
possessed by the air or its contained vapor. The 
small difference of potential of the exceedingly 
small drops of water in clouds is enormously in- 
creased by the union or coalescing of many 
thousands of such drops into a single rain drop. 
(See Electricity, Atmospheric.) 

Exchange, Telephonic, System of 

— A combination of circuits, switches and 
other devices, by means of which any one of 
a number of subscribers connected with a 
telephonic circuit, or a neighboring telephonic 
circuit or circuits, may be placed in electrical 
communication with any other subscriber 
connected with such circuit or circuits. 

A telephone exchange consi-ts essentially of a 
multiple switchboard, or a number of multiple 
switchboards, furnished with spring-jacks, an- 
nunciator drops, and suitable coJinecting cords. A 
call bell, or bells, is also provided. The annun- 
ciator drops are often omitted. (See Board^ 
Multiple Switch. ) 

Excitability. Electric, of Nerve or Mus- 

cnlar Fibre The effect produced by an 

electric current in stimulating the nerve of a 



Exc] 



222 



[Exh. 



living animal, or in producing an involuntary 
contraction of a muscle. 

Du Bois-Reymond has shown that these effects 
depend : 

(i.) On the strength of the current employed. 
The excitability occurs only when the current 
begins to flow, and when it ceases flowing; or, 
when the electrodes first touch the nerves, and 
when they are separated from it. Subsequent 
investigations have shown that this is true only 
for the frog's nerves, and is true for the human 
nerves only in the case of moderate currents, 
strong currents producing tetanus. 

(2.) On the rapidity with which the current 
used reaches its maximum value, that is, on the 
rapidity of change of current density. (See 
Current Density.) 

Excitability, Electro-Nervous — 

In electro-therapeutics the electric excitation 
of a nerve. 

Excitability, Electrotonic — The 

actual excitability of a nerve when in the 
electrotonic condition. (See Electrotonus. 
Anelectrotonus. Kathelectrotonus.) 

Excitability, Faradic — Muscular or 

nervous excitability following the employment 
of the rapidly intermittent currents produced 
by induction coils. (See Coil, Induction?) 

Faradic excitability is different from galvanic 
excitability ; or that produced by means of a con- 
tinuous voltaic current. (See Excitability, Gal- 
vanic. ) 

Excitability, Galvanic —A term 

sometimes employed for electric excitability 
of nerve or muscular fibre. (See Excitability, 
Electric, of Nerve or Muscular Fibre?) 

Excitation, Compensated, of Alternator. 
— (See Alternator, Compensated Excitation 
of.) 

Excitation, Direct — The excitement 

of a muscle by placing an electrode on the 
muscle itself. 

Excitation, Electro-Muscular — 

In electro-therapeutics the galvanic or faradic 
excitation of the muscle, or its excitation by 
the continuous currents of a voltaic battery, or 
the alternating currents of an induction coil. 

Excitation, Faradic — Excitation of 

muscle or nerve fibre by means of rapidly 



alternating currents of electricity. (See* 
Excitability, Faradic?) 

Excitation, Indirect The excite- 
ment of a muscle from its nerve. 

Exciter of Field.— (See Field, Exciter of.) 

Exciting Liquid of Voltaic Cell.— (See 
Cell, Voltaic, Primary, Exciting Liquid of .) 

Execution, Electric Causing the 

death of a criminal, in cases of capital pun- 
ishment, by means of the electric current. 

Electric execution has been adopted by the 
State of New York, in accordance with the 
following law : 

"The Court shall sentence the prisoner to' 
death within a certain week, naming no day or 
hour, and not more than eight nor less than five 
weeks from the day of sentence. The execution 
must take place in the State prison to which con- 
victed felons are sent by the Court, and the execu^ 
tioner must be the agent and warden of the prison. 

"No newspaper may print any details of the 
execution, which is to be inflicted by electricity. 
A current of electricity is to be caused to pass 
through the body of the condemned of sufficient 
intensity to kill him, and the application is to be: 
continued until he is dead." 

Exhaustion, Electric Physiological 

effects resembling those produced by sun- 
stroke, resulting from prolonged exposure 
to the radiation of unsually large voltaic arcs.. 
(See Sun-Stroke, Electric.) 

Exhaustion of Primary Voltaic Cell.— 
(See Cell, Voltaic, Primary, Exhaustion of)< 

Exhaustion of Secondary Voltaic Cell. — 

(See Cell, Voltaic, Secondary, Exhaustion oj ".) 

Exhaustion of Voltaic Cell.— (See Cell* 

Voltaic, Exhaustio7i of.) 

Exhaustion, Reaction of A con- 
dition of nervous and muscular irritability to 
electric excitation when a certain reaction, 
produced by a given current strength, cannot 
be reproduced without an increase of current 
strength. 

The reaction of exhaustion may be regarded as 
a special variety of the reaction of degeneration. 
(See Degeneration, Reaction of.) 

The reaction of degeneration embraces the 
following modifications of irritability, viz.: 



Exp. J 223 

(i.) Disappearance or diminution of nervous 
irritability to both galvanic and farad ic currents. 

(2.) Disappearance of far die and increase of 
galvanic irritability of muscles, generally associ- 
ated with an increase of mechanical irritability. 

(3 ) Disappearance of faradic and increase of 
galvanic muscular irritability associated generally 
with increased mechanical irritability. 

(4.) Tardy, delayed contraction of muscles in- 
stead of quick reaction of normal muscle. 

(5.) Marked modifications of normal sequence 
of contraction. — Liebig &° Rohe. 

Expanding Magnetic Whirl. — (See 
Whirl, Exficuiding Magnetic.) 

Expansion, Co-efficient of The 

fractional increase in the dimensions of a bar 
or rod when heated from 32 degrees to 33 
degrees F. or from o degree to 1 degree C. 

The fractional increase in the length of the bar 
is called the Co -efficient of Linear Expansion. 

The fractional increase in the surface is called 
the Co-efficient of Surface Expansion. 

The fractional increase in the volume is called 
the Co-efficient of Cubic Expansion. 

Expansion, Electric The increase 

in volume produced in a body on giving such 
body an electric charge. 

A Ley den jar increases in volume when a 
charge is imparted to it. This result is due to an 
expansion of the glass due to the electric charge. 
According to Quincke, some substances, such as 
resinous or oily bodies, manifest a contraction of 
volume on the reception of an electric charge. 

Expansion Joint. — (See Joint, Expan- 
sion^ 

Expansion, Linear, Co-efficient of 

A number expressing the fractional increase in 
length of a bar for a given increment of heat. 

The co-efficients of expansion of a few sub- 
stances are given in the following table: 

Temp. 

Aluminium 16 to 100 degrees C. .0.0000235 

Brass o -> 100 " " ..0.0000188 

Copper o •' 100 " '* ..0.0000167 

German silver., o- 100 4< " ..0.0000184 

Glass o '• 100 " " ..0.0000071 

Iron 13" 100 " " ..0.0000123 

Lead o" 100 "• " ..0.0000280 

Platinum o" 100 " " . 0.0000089 

Silver o" 100 " " ..0.0000194 

Zinc o" 100 " " .0.0000230 

— {Anthony &> Brackett.) 



[Eye. 



Exploder, Electric Mine A small 

magneto-electric machine used to produce the 
currents of high electromotive force employed 
in the direct firing of blasts. 

Exploder, Electro-Magnetic —A 

small magneto-electric machine used to pro- 
duce the currents of high electromotive force 
employed in the direct firing of blasts. 

Explorer, Electric An apparatus 

operated by means of induced currents, and 
employed for the purpose of locating bullets 
or other foreign metallic substances in the 
human body. (See Balance, Induction, 
Hughes '.) 

Explorer, Magnetic A small, flat 

coil of insulated wire, used, in connection with 
the circuit of a telephone, to determine the 
position and extent of the magnetic leakage 
of a dynamo-electric machine or other similar 
apparatus. (See Magnetopho?ie.) 

Explosive Distance. — (See Distance, Ex- 
plosive.) 

Extension Call-Bell.— (See Bell, Exten- 
sion Call.) 

External Circuit. — (See Circuit, Exter- 
nal.) 

External Secondary Resistance. — (See 
Resistance, Exterfial Secondary ) 

Extra Currents.— (See Currents, Extra.) 

Extraordinary Resistance. — (See Resist- 
ance, Extraordinary ■.) 

Extra-Polar Region. — (See Region, Ex- 
tra-Polar.) 

Eye, Electro-Magnetic A term pro- 
posed for a certain form of spark-micrometer 
employed by Hertz in his experiment on elec- 
tro-magnetic radiation. 

This apparatus has received the above name 
because it enables the observer to see or localize 
an electromagnetic disturbance. 

The particular spark -micrometer that has re- 
ceived the name of the electro-magnetic eye had 
the form of a circle 35 centimetres in radius, and 
was formed of a copper wire 2 millimetres in di- 
ameter. Like all spark-micrometer circuits, it 
had its terminals separated by a small air-space. 

Eye, Selenium An artificial eye in 



Fac] 

which a selenium resistance takes the place 
of the retina and two slides the place of the 
eyelids. 

The selenium resistance is placed in the circuit 
of a battery and a galvanometer. When the 
slides L, L, Fig. 244, are shut, the galvanometer 
deflection is less than when they are open. 

The opening of the aperture between the slides 
L, L, may be automatically accomplished by the 
action of the light itself, by moving them by an 
electro-magnet placed in the circuit of a local bat- 
tery, and a selenium resistance maybe so arranged 
that when light falls on it the slides L, L, are 
moved together, and when the amount of such 
nght is small they are moved apart, by the action 



224: 



[Far. 



of a spring. In this way there is obtained a 
device roughly resembling the dilatation or con- 




Fig 244- Selenium Eye. 

traction of the pupil of the eye from the action of 
light on the iris. (See Photometer, Selenium.) 



Fac-Simile Telegraphy, or Panteleg- 
raphy. — (See Telegraphy, Fac-Simile.) 

Fahrenheit's Thermometer Scale. — (See 
Scale, Thermometer, Fahrenheit's.) 

Fall of Potential.— (See Potential, Fall 
of.) 

False Magnetic Pole (See Pole, 

Magnetic, False.) 

False Resistance. — (See Resistance, 
False.) 

False Zero.— (See Zero, False) 

Fan Guard. — (See Guard, Fan) 

Farad. — The practical unit of electric 
capacity. 

Such a capacity of a conductor or condenser 
that one coulomb of electricity is required to 
produce in the conductor or condenser a 
difference of potential of one volt. 

As in gases, a quart vessel will hold a quart of 
gas under unit pressure of one atmosphere, so, in 
electricity, a conductor or condenser, whose capa- 
city is one farad, will hold a quantity of electricity 
equal to one coulomb when under an electromotive 
force of one volt. 

It may cause some perplexity to the student to 
understand why there should be in electricity one 
unit of capacity to represent the size of the vessel 
or conductor, and another to represent the 
amount or quantity of electricity required to fill 



such vessel. But, like a gas, electricity acts, in 
effect, as if it were very compressible, so that the 
quantity required to fill any condenser will de- 

P' 




Fig 245. Elevation of Standardized Condenser. 
pend on the electromotive force under which it is 
put into the conductor cr condenser. 

For purposes of measurement, capacities of 
conductors are compared with those of condensers 




Fig. 24b. Plan 0/ Standardized Condenser. 

whose capacities are known in microfarads, or 
fractions thereof. The microfarad, or the 

of a farad, is used because of the very 



1,000,000 

great size of a farad. 



JTai\ 



225 



[Fail. 



Fig. 245 shows an elevation, and Fig. 246 a 
plan of the form often given to a standardized 
condenser or microfarad. The condenser is 
charged by connecting the terminals of the elec- 
tric source to the binding posts N and N. It is 
discharged by means of the plug key P', that 
connects the brass pieces A and B, when pushed 
firmly into the conical space between them. 

The condenser is made by placing sheets of tin 
foil between sheets of oiled silk or mica in the 
box and connecting the alternate sheets to one of 
the brass pieces B, and the other set to the brass 
piece A, as will be better understood from an 
inspection of Fig. 247. 

b 



Fig. 24J Method of Construction of a Condenser. 

Condensers are generally made of the capacity 
of the i of a microfarad. Sometimes, however, 
they are made so that either all or part of the 
condenser may be employed, by the insertion of 
the different plug keys. 

The form of condenser shown in Fig. 248 is 




Fig. 248 . Standard Condenser 

capable of ready division into five separate val- 
ues, viz.: .05, .05, .2, .2 ami .5 microfarad. 

Farad, 3Iicro The millionth part 

of a farad. (See Farad.) 

Faraday Effect— (See Effect, Faraday.) 
Faraday's Cube. — (See Cube, Faraday s.) 



Faraday's Dark 

Dark, Faraday s) 

Faraday's Net. — (See 

Faradic Apparatus, 

(See Apparatus, 

neto-Electric.) 

Faradic Brush.— (See 

Current 



Space.— (See Space, 



Net, Faraday s.) 

Mag-neto-Electric 

Faradic. Mag- 

Brush, Faradic ) 



(See Current Fara- 
Excitation. — (See Excitation. 



Faradic 

die) 

Faradic 

Faradic) 

Faradic Induction Apparatus. — (See 
Apparatus, Faradic Induction.) 

Faradic Irritability. — (See Irritability, 
Faradic.) 

Faradic Machine. — (See Machine, Fara- 
dic.) 

Faradization. — In electro-therapeutics, the 
effects produced on the nerves or muscles 
by the use of a faradic current, in order to 
distinguish such effects from galvanization 
or those produced by a voltaic current. (See 
Galvanization.) 

Faradization, General A method 

of applying the faradic current similar to 
that employed in general galvanization. 
(See Galvanization, General.) 

Faradization, Local A method of 

applying the faradic current in general simi- 
lar to that employed in local galvanization. 
(See Galvanization, Local.) 

Fault. — Any failure in the proper working 
of a circuit due to ground contacts, cross- 
contacts or disconnections. (See Contacts. 
Cross.) 

Faults are of three kinds, viz. : 

(1.) Disconnections. (See Disconnection.) 

(2.) Earths. (See Earth.) 

(3.) Contacts. (See Contacts.) 

Various methods are employed for detecting 
and localizing faults, for the explanation of 
which reference should be had to standard elec- 
trical works on testing or measurements. 

Fault, Ironwork, of Dynamo A 

ground or connection between the current of 
a dynamo and any part of its ironwork. 



Fau.J 



22T6 



[Fie. 



If the dynamo is in good connection with the 
ground, as is frequently the case in marine plants, 
this fault is the same as a ground. 

Faults, Localization of Determin- 
ing the position of a fault on a telegraph line 
or cable by calculations based on the fall in 
the potential of the line measured at different 
points, or by loss of charge, etc. 

For details, see standard works on electrical 
measurements. 

Feed, Clockwork, for Arc Lamps 

An arrangement of clockwork for obtaining 
a uniform feed motion of one or both elec- 
trodes of an arc lamp. 

The clockwork is automatically thrown into or 
out of action by an electro-magnet, usually placed 
in a shunt circuit around the carbons. 

Feed, To To supply with an electric 

current, as by a dynamo or other source. 

Feeder.— One of the conducting wires or 
channels through which the current is dis- 
tributed to the main conductors. 

Feeder, Standard or Main The 

main feeder to which the standard pressure 
indicator is connected, and whose pressure 
controls the pressure at the ends of all the 
other feeders. 

The term pressure in the above definition is 
used in the sense of electromotive force or differ- 
ence of potential. 

Feeder-Wires. — (See Wires, Feeder?) 
Feeders. — In a system of distribution by 
constant potential, as in incandescent elec- 
tric lighting, the conducting wires extend- 
ing between the bus-wires or bars, and the 
junction boxes. 

A feeder differs from a main in that a main 
consists of a conductor that maybe tapped at any 
point to supply a customer, while a feeder leads 
direct from the dynamo or other source to a main 
and is not tapped at any point. 

Feeders, Negative The feeders 

that are connected with the negative terminal 
of the dynamo. (See Feeders?) 

Feeders, Positive The feeders that 

are connected with the positive terminal of 
the dynamo. (See Feeders?) 



Feeding Device of Electric. Arc Lamp. — 

(See Device, Feeding, of art Arc La?np. 
Feed, Clockwork, for Arc-Lajnps?) 

Feeding-Wire. — (See Wire, Feeding^ 

Feet, Ampere The product of the 

current in amperes by the distance in feet 
through which that current passes. 

It has been suggested that the term ampere- 
feet should be employed in expressing the strength 
of electro-magnetism . in the field magnets of 
dynamo-electro machines or other similar ap- 
paratus. 

Ferranti Effect.— (See Effect, Ferranti) 

Ferro-Magnetic Substance. — (See Sub- 
stance, Ferro-Magnetic?) 

Fibre, Quartz A fibre suitable for 

suspending galvanometer needles, etc., made 
of quartz. 

The quartz fibre is obtained by fusing quartz and 
drawing out the fused material as a fine thread, 
in a manner similar to the production of glass 
fibres. Quartz fibres possess marked advantage 
over silk fibres, in that they are 5.4 times stronger 
for equal diameters, and especially, in that they 
return to the zero point, after very considerable 
deflections. 

Quartz fibres are readily obtained by fusing 
quartz pebbles together in the voltaic arc, and 
drawing them apart with a rapid, but steady, uni- 
form motion. 

Fibre Suspension. — (See Suspension, 
Fibre.) 

Fibre, Tulcanized A variety of in- 
sulating material suitable for purposes not 
requiring the highest insulation. 

Vulcanized fibre is, however, seriously affected 
by long exposure to moisture. 

Fibrone. — An insulating substance. 

Field, Air That portion of a mag- 
netic field in which the lines of force pass 
through air only. 

Field, Alternating An electrostatic 

or magnetic field the positive direction of the 
lines of force in which is alternately reversed 
or changed in direction. 

Field, Alternating Electrostatic 

An electrostatic field, the potential of which 
is rapidly alternating. 



Tie.] 



227 



[Fie. 



An alternating electrostatic field is, according 
to Tesla's experiments, produced in the neighbor- 
hood of the terminals of the secondary of an in- 
duction coil, through whose primary, alternations 
of high frequency are passing. 

Field, Alternating 1 Magnetic. — A mag- 
netic field the direction of whose lines of 
force is alternately reversed. 

Field, Density of The number of 

lines of force that pass through any field, per 
unit of area of cross-section. 

Field, Electric A term sometimes 

used in place of an electrostatic field. (See 
Field, Electrostatic?) 

Field, Electro-Magnetic The space 

traversed by the lines of magnetic force pro- 
duced by an electro-magnet. (See Field, 
Magnetic.) 

Field, Electrostatic The region of 

electrostatic influence surrounding a charged 
body. 

Electrostatic attractions or repulsions take 
place along certain lines called lines of electro- 
static force. These lines of force produce a field 
called an electrostatic field. Electric level or 
potential is measured along these lines, just as 
gravitation levels are measured with a plumb line 
along the lines of gravitation force. (See Poten- 
tial, Electric.) 

Work is done when a body is moved along the 
lines of electrostatic force in a direction from an 
oppositely charged body, or towards a similarly 
charged body, just as work is done against 
gravity when a body is moved along the lines of 
gravitation force, away from the earth's centre, 
or vertically upwards. 

Field; Exciter of In a separately 

excited dynamo-electric machine, the dyna- 
mo-electric machine, voltaic battery, or other 
electric source employed to produce the field 
of the field magnets. (See Machine, Dyna- 
mo-Electric.) 

Field, Intensity of The strength 

of a field as measured by the number of lines 
of force that pass through it per unit of area 
■of cross-section. (See Field, Electrostatic. 
Field, Magnetic.) 

Field, Magnetic The region of 



magnetic influence surrounding the poles of a 
magnet. 

A space or region traversed by lines of 
magnetic force. 

A place where a magnetic needle, if free 
to move, will take up a definite position, under 
the influence of the lines of magnetic force. 

Unit strength of magnetic field is the field 
which would be produced by a magnetic pole of 
unit strength at unit distance. 

Magnetic attractions and repulsions are assumed 
to take place along certain lines called lines of 
magnetic force. The directions of these lines in 
any plane of a magnetic field may be shown by 
sprinkling iron filings over a sheet of paper held 
in a horizontal position to a magnet pole inclined 




Fig. 24Q. Magnetic Field. 

to the paper in the desired plane and then gently 
tapping the paper. 

The groupings of iron filings so obtained are 
sometimes called magnetic figures. 

The directions of the lines of force thus shown 
will appear from an inspection of Fig. 249, taken 
in a plane joining the two poles of a straight bar 
magnet, and Fig. 250, taken in a plane at right 
angles to the north pole of a straight bar magnet. 

In Fig. 249, the repulsion of the lines of force 
at either pole is shown by the radiation of the 
chains ot magnetized iron particles. The mutual 
attraction of unlike polarises is shown by the 
curved lines. 

In Fig. 250, the repulsion of the similarly mag- 
netized chains is clearly shown. 

Lines of magnetic force are assumed to pass 
out fr 077i the north pole and back again into the 
magnet at its south pole. This assumed direction 



Fie.] 



228 



[Fie. 



is called the direction of the lines of magnetic 
force. 

Faraday expressed his conception of lines of 
magnetic force as follows: 

" Every line of force must therefore be consid- 
ered as a closed circuit, passing, in some part of 
its course, through a magnet and having an equal 
amount of force in every part of its course. There 




Fig., 250. Magnetic Field. 

exist lines of force within the magnet of the same 
nature as those without. What is more, they are 
exactly equal in amount to those without. They 
have a relation in direction to those without and 
are, in fact, continuations of them." 

When a conductor, such as a wire through 
which a powerful current of electricity is flowing, 
is dipped in a mass of iron filings, a chain of iron 
filings is formed, the north end of which is urged 
around the conductor in one direction and the 
south end in the opposite direction, so that the 
movable chain of filings surrounds or grips the 
conductor in concentric rings or circles. 

The density of a magnetic fi 'eld is directly pro- 
portional to the nu.nber of lines of f >rce per unit 
of area of cross-section. 

A single line of force, or a unit line of force, is 
such an intensity of fie'd as exists in each square 
centimetre of cross-section of a unit magnetic 
field. 

A magnetic field is uniform, or possesses uni- 
form intensity, when it possesses the same num- 
ber of lines of force per square centimetre of area 
of cross-section. 

Field, Magnetic, Alternating- The 

magnetic field produced by means of an 
alternating current. 



Field, Magnetic, Dissymmetrical 

A field whose lines of force are not symmet- 
rically distributed in adjacent halves. 

Field, Magnetic, Expanding of 

An increase in the length of the lines of mag- 
netic force in any field, or an increase in the 
length of their magnetic circuit. 

Field, Magnetic, of an Electric Current 
The magnetic field surrounding a cir- 




Fig. 251. Field of Current. 

cuit through which an electric current is flow- 
ing. 

An electric current produces a magnetic field. 
This was discovered by Oersted 
in 18 19, and may be shown by 
sprinkling iron filings on a sheet 
of paper, placed on the wire 
conductor conveying the cur- 
rent, at right angles to the direc- 
tion in which the current is pass- 
ing. Here the lines of force 
appear as concentric circles, ex- 
tending around the conductor, 
as shown in Fig. 251. Their 
direction, as regards the length 
of the conductor, is shown in 
Fig. 252. The electric current 
sets up these magnetic whirls 
around the conductor on its 
passage through it. 

The direction of the lines of ^ 

J J Fig. 252. Direc- 

magnetic force produced by an tion / Lines of 
electric current, and hence its Force, 
magnetic polarity, depends on the direction in 
which the electric current flows. This direction; 




Fie.] 



229 



[Fie. 



may be remembered as follows: If the current 
flows towards the observer, the directions of the 
lines of magnetic force is opposite to that of the 
hands of a watch, as shown in Fig. 253. 



^LQJUU^^r 




Fig 253. Direction of Lines 0/ Force, 

It is from the direction of the lines of magnetic 
force that the polarity of a helix carrying a cur- 
rent is deduced. (See Solenoid, Magnetic. Mag. 
net, Electro.) 

A magnetic field possesses the following prop- 
erties, viz.: 

(1.) All magnetizable bodies are magnetized 
when brought into a magnetic field. (See Induc- 
tion, Magnetic.) 

(2.) Conductors moved through a magnetic 
field so as to cut its lines of force have differences 
of potential generated m them at different points, 
and if these points be connected by a conductor, 
an electric current is produced. (See Induction, 
Electro-Magnetic . ) 

Field, Magnetic, Pulsatory A field, 

the strength of which pulsates in such manner 
as to produce oscillatory currents by induc- 
tion. 

Field, 3Iagnetic, Reversing That 

portion of the field of a dynamo-electric ma- 
chine, produced by the field-magnet coils, in 
which the currents flowing in the armature 
coils are stopped or reversed after the coil has 
passed its theoretical position of neutrality. 

Sparkless commutation is obtained by placing 
the brushes on the commutator so as to corre- 
spond with the reversing field. 

Field, Magnetic, Shifting A term 

proposed by Professor Elihu Thomson to ex- 
press a field of magnetic lines of changing 
position with respect to the axis of the pole 
from which they emanate. 

A shifting magnetic field is especially a phe- 
nomenon of a rapidly alternating magnetic field 



occurring in a substance like hardened steel in 
which the coercive force is fairly nigh. If, for 
example, a single magnet pole of an electro- 
magnet, whose coils are traversed by a rapidly 
alternating current of electricity, is placed near one 
end of a steel file, the changing polarity developed 
thereby moves or shifts from the point directly 
over the pole towards the distant end. The 
presence of this shifting field can be shown by the 
rotation of discs of copper suitably inclined to uhe 
end of the file. In a similar manner a prismatic 
mass of steel, placed with one of its flat sides 
on the pole of a rapidly alternating magnetic 
field, will have a magnetic field developed in it, 
which will move or shift from the flat base 
towards the upper edge. Movable masses of good 
conducting metal, such as copper, will be set in 
rotation in a direction such as would be caused 
by an escape of gas therefrom. 

The shifting magnetic field travels from the 
upper portions of the prism just as a stream of 
escaping gaseous substance would. 

Field, Magnetic, Spreading-Out A 

term sometimes used to represent an expand- 
ing magnetic field. (See Field, Magnelic, 
Expanding of,) 

Field, Magnetic, Stray That por- 
tion of the field of a dynamo-electric machine 
which is not utilized for the development of 
differences of potential in the armature, be- 
cause its lines of force do not pass through 
the armature. 

Field, Magnetic, Strength of The 

dynamic force acting on a free magnetic pole, 
placed in a magnetic field. 

If a free magnetic pole could be placed in a 
magnetic field, it would begin to move towards 
the opposite pole of the field, under its magnetic 
attraction, just as an unsupported body, free to 
move, would begin to fall towards the earth. 
The strength of a magnetic field corresponds to 
the acceleration of the force of gravity in the 
case of a falling body. The strength of the mag- 
netic pole corresponds to the mass of the falling 
body. The force impressed in the case of the 
magnetic field is equal to the strength of the pole 
multiplied by the strength of the field. 

Field, Magnetic, Symmetrical A 

field whose lines of force are symmetrically 
distributed in adjacent halves. 



Fie.] 



230 



[Fil. 



Field, Magnetic, Uniform 



■A field 



traversed by the same number of lines of 
magnetic force in all unit portions of area of 
cross-section. (See Field, Magnetic) 

Field, Magnetic, Waste A term 

sometimes employed for stray field. (See 
Field, Magnetic, Stray) 

Field, Rotating-Cnrrent A mag- 
netic field produced by means of a rotating 
current. (See Current, Rotating') 

Field, Uniform Density of A uni- 
form density in all equal areas of cross- 
section of field. 



Field, Yortex-Ring 



-The field of 



influence possessed by a vortex-ring. 

Professor Dolbear points out the fact that the 
direction of the rotation of a fluid constituting a 
vortex-ring resembles the magnet flux in a mag- 
netic field, and shows, from the action of such rings 
on one another, that they possess a true field, or 
atmosphere of influence outside their actual 
bodies. He infers that such rings possess true 
polarity, since the motions producing them have 
different directions on opposite sides or ends. 

Figure of Merit of Galvanometer. — (See 
Galvanometer, Figure of Merit of) 

Figures, Breath Faint figures of 

condensed vapor produced by electrifying a 
coin, placing it momentarily on the surface of 
a sheet of clean, dry glass, and then breath- 
ing gently on the spot where the coin was 
placed. 

The moisture collects on the electrified portions 
of the plate and forms a fairly distinct image of 
the coin. 



Figures, Electric 



-Figures of various 



shapes produced on electrified surfaces by the 
arrangement of dust particles or vapor 
vesicles under the influence of electric charges. 

Electric figures are of two varieties, viz.: 

(i.) Dust figures. 

(2.) Breath figures. 

Figures, Lichtenberg's Dust — 

Figures produced by writing on a sheet of shel- 
lac with the knob of a charged Leyden jar and 
then sprinkling over the sheet dried and 
powdered sulphur and red lead, which have 



been previously mixed together, and are so 
rendered, respectively negative and positive. 

The red lead collects on the negative parts of 
the shellac surface, and the sulphur on the posi- 
tive parts, in curious figures, known as Lichten- 
berg's Dust Figures, one of which is shown in 
Tig- 254. 




Fig. 254- Lichtenberg's Dust Figures. 

These figures show very clearly that an electric 
charge tends to creep irregularly over the surface 
of an insulating substance. 

Figures, Magnetic A name some- 
times applied to the groupings of iron filings 
on a sheet of paper so held in a magnetic field 
as to be grouped or arranged under the in- 
fluence of the lines of force of the same. (See 
Field, Magnetic) 

Filament— A slender thread or fibre. 
The term is applied generally to threads or 
fibres varying considerably in diameter. 

Filament, Current A term some- 
times employed in place of current streamlet. 
(See Streamlets, Current) 

Filament, Magnetic A polarized 

line or chain of ultimate magnetic particles. 

This is sometimes called a unifor?n magnetic 
filament. 

A bar-magnet possesses but two free poles. 
When broken ai its neutral point or equator, the 
bar will develop free poles at the broken ends. 
This is explained by considering the magnet to 
be composed of a number of separate particles, 
separately magnetized. A single chain or fila- 
ment of such particles is called a magnetic 
filament. (See Magnet, Neutral Point of. Mag' 
netism, Hughes' Theory of. Magnetism, 
Ewing^s Theory of.) 

Filament of Incandescent Electric Lamp. 



Ml.] 



231 



[Fir. 



— (See Lamp, Incandescent Electric, Fi 'la- 
ment of.) 
Filament, Uniform Magnetic A 

term sometimes applied to a magnetic fila- 
ment. (See Filament, Magnetic.) 

Filaments, Flashed Filaments for 

an incandescent lamp, that have been sub- 
jected to the flashing process. (See Carbons, 
Flashi?ig Process fori) 

Filamentous Armature Core. — (See Core, 
Armature, Filamentous.) 

Film Cut-Out— (See Cut-Out, Film) 

Finder, Induction A term some- 
times employed for a magnetic explorer. 

Finder, Position, Electric A de- 
vice by means of which the exact position of 
an object can be obtained. 

By means of a position -finder a gunner can 
be telephoned or otherwise ordered to fire at ob- 
jects he cannot see, and yet obtain a fair degree 
of accuracy. 

Finder, Range, Electric A de- 
vice by means of which the exact distance of 
an enemy's ship or other target can be readily 
determined. 

The operation of an electric range-finder is based 
on a method somewhat similar to the solving of a 
triangle for the purpose of determining distances. 
If the base line of a triangle and the two angles 
at the base are known, the other two sides and 
the included angle can be determined. 

In the range-finder, the resistance of a German 
silver wire corresponds to the graduated arc of 
the theodolite used to measure the angles, and a 
rheostat, as a receiving instrument, measures the 
values of the angles. The base line is a constant, 
so that the receiving instrument is marked in 
yards instead of angles. To use the range-finder, 
two observers watch the target object continu- 
ously through a telescope. They do this and 
nothing else, while a third observer watches a 
galvanometer and so alters a resistance, by moving 
a contact or slide key along a resistance wire, as 
to keep the needle of the galvanometer constantly 
at zero. The exact distance being thus ascer- 
tained, the gunner can make the proper allowance 
in firing. 

Finder, Wire Any form of galva- 
nometer used to locate or find the corre- 



sponding ends of different wires in a bunched 
cable. 

The different wires in a cable are usually tagged 
and numbered at the end of the cable and at the 
joints. The telephone has been successfully em- 
ployed as a wire finder. 

Fire Alarm Annunciator. — (See Annun- 
ciator, Fire Alar??t) 

Fire Alarm, Automatic (See 

Alarm, Fire Autojnatic) 

Fire Alarm Contact. — (See Contact, Fire 
Alarm) 

Fire Alarm Signal Box. — (See Box, Fire 
Alarm Signal.) 

Fire Alarm Telegraph Box. — (See Box, 
Fire Alarm Telegraph.) 

Fire Ball.— (See Ball, Fire) 

Fire Cleansing. —(See Cleansing, Fire) 

Fire Extinguisher, Electric A 

thermostat or mercury contact, which auto- 
matically completes a circuit and turns on a 
water supply for extinguishing a fire, on a 
certain predetermined increase of tempera- 
ture. 

Fire, Hot, St. Elmo's A term pro- 
posed by Tesla for a form of powerful brush 
discharge between the secondary terminals of 
a high frequency induction coil. (See Dis- 
charge, Brush-and- Spray) 

This form of St. Elmo's fire differs from the 
ordinary form in being hot. Its general appear- 
ance is shown in Fig. 255, taken from Tesla. 




Fig. 255. St. Elmo's Hot Fire. 

Describing its production he says : 'In many of 
these experiments, when powerful effects are 
wanted for a short time, it is advantageous to use 



Fir.] 



232 



[Flo. 



iron cores with the primaries. In such case a 
very large primary coil may be wound and placed 
side by side with the secondary, and, the nearest 
terminal of the latter being connected to the 
primary, a laminated iron core is introduced 
through the primary into the secondary as far as 
the streams will permit. Under these conditions 
an excessively powerful brush, several inches 
long, which may be appropriately called ' St. 
Elmo's hot fire,' may be caused to appear at the 
other terminal of the secondary, producing strik- 
ing effects. It is a most powerful ozonizer ; so 
powerfuL indeed, that only a few minutes are suf- 
ficient to fill the whole room with the smell of 
ozone, and it undoubtedly possesses the quality of 
exciting chemical affinities." 

Fire, St. Elmo's Tongues of faintly 

luminous fire which sometimes appear on the 
pointed ends of bodies in connection with the 
earth, such as the tops of church steeples or 
the masts of ships. 

The appearance of the St. Elmo's fire is due to 
brush discharges of electricity. 

Fishes, Electric A term applied to 

various fishes, such as the eel and the ray, 
which possess the ability of protecting them- 
selves by giving electric shocks to objects 
touching them. (See Eel, Electric.) 

Fishing" Box. — (See Box, Fishing) 

Fitting's or Fixtures, Electric Light 

— The sockets, holders, arms, etc., required 
for holding or supporting incandescent electric 
lamps, 

Fixed Secondary. — (See Secondary, 
Fixed.) 

Fixtures, Telegraphic A term gen- 
erally limited to the variously shaped supports 
provided for the attachment of telegraphic 
wires. 

Fixtures, Telegraphic House-Top 

Telegraphic fixtures placed on .the roofs of 
buildings for the support of the lines. 

Flaming Discharge. — (See Discharge, 
Flaming.) 

Flash, Side A sparking or lateral 

discharge taking place from the sides of a 
conductor, when an impulsive rush of elec- 
tricity passes through it. 



The phenomenon of siae flashing is due to a. 
lateral discharge which takes the alternative path, 
instead of a path of much smaller ohmic resist- 
ance. The tendency to side flash results from 
the fact that the metallic circuit possesses induct- 
ance. (See Path, Alternative. Discharge, Lat- 
eral. Inductance. ) 

Flashed Carbons. — (See Carbons, 
Flashed.) 

Flashed Filaments. — ( See Filame7its, 
Flashed?) 

Flashes, Auroral — Sudden variations 

in the intensity of the auroral light. 

Intermittent flashes of auroral light that 
occur during the prevalence of an aurora. 
(See Aurora Borealis.) 

Flashing of Carbons, Process for the 

— (See Carbons, Flashing Process for.) 

Flashing of Dynamo-Electric Machine. — 

(See Machine, Dynamo-Electric, Flashing 
of) 

Flat Cable.— (See Cable, Flat) 

Flat Duplex Cable.— (See Cable, Flat 
Duplex) 

Flat Ring Armature. — (See Armature,. 
Flat Ring.) 

Flats. — A name sometimes applied to those 
parts of commutator segments the surface of 
which, through wear, has become lower than 
the other portions. (See Cojnmutator) 

Fleming's Gauss. — (See Gauss, Flem- 
ing's) 

Fleming's Standard Yoltaic Cell. — (See 
Cell, Voltaic, Standard, Fleming s.) 

Flexible Electric Light Pendant.— (See 
Pendant, Flexible Electric Light) 

Flexible Lead.— (See Lead, Flexible) 

Floating Battery, De la Rive's.— (See 
Battery Floating, De la Rives) 

Flow.— In hydraulics, the quantity of 
water or other fluid which escapes from an 
orifice in a containing vessel, or through a 
pipe, in a given time. 

Flow-Lines of Escaping Fluid. — Lines 
within the mass of a fluid in motion, drawn at 



Tlo.] 



233 



[Fly. 



a number of points, so that the flow at any 
instant is tangential at such points to the 
curved path. 

Flow, Magnetic — The magnetic 

flux. (See Flux, Magnetic.) 

Flow of Current, Assumed Direction of 

— (See Current, Assumed Direction 

of Flow of.) 

Flow of Energy. — (See Energy, Flow of.) 
Flow of Lines of Electrostatic Force. — 

(See Force, Electrostatic, Lines of, Assumed 
Flow of) 

Flow of Magnetic Induction. — (See In- 
duction, Magnetic, Flux or Flow of.) 

Fluid, Depolarizing An electro- 
lytic fluid in a voltaic cell that prevents polari- 
sation. (See Cell, Voltaic, Polarisation of) 

Fluid Insulator. — (See Insulator., Fluid) 

Fluoresce. — To become self-luminous 
when exposed to light. 

A body is said to fluoresce when it shines, by 
means of the light it produces. In this respect it 
differs from an illumined body, which shines by 
reflected light. 

Fluorescence. — A property possessed by 
certain solid or liquid substances of becoming 
self-luminous while exposed to light. 

In fluorescence the refrangibility of rays of 
light is changed. The invisible rays beyond the 
violet, the ultra-violet, become visible, so that 
the light is transformed, the particles absorbing 
one wave length and emitting another. (See Incan- 
descence. ) 

Canary glass, or glass colored yellow by oxide 
of uranium, or a solution of sulphate of quinine, 
possesses fluorescent properties. The path of a 
pencil of light brought to a focus in either of these 
substances, or a beam or cone of li^ht passed 
through them, is rendered visible by the particles 
lying in this path becoming self-luminous. The 
path of a beam of light entering the dusty air of 
a darkened chamber is visible from the light being 
diffused or scattered in all directions by the float- 
ing dust particles. 

In a fluorescent substance, the path of the light 
is also rendered visible by the particles -which lie 
in its path, throwing out light in all directions. 
There is, however, this difference, that in the 



case of the dust particles the light which comes 
directly from the beam is reflected ; while in the 
case of the fluorescent body the light comes from 
the particles themselves, which are set into vibra - 
tion by the light that is passing through, and has 
been absorbed by their mass. 

Fluorescence is, therefore, a variety of phos- 
phorescence. (See Phosphorescence.) 

Fluorescent. — Possessing the capability of 
fluorescing. 

Fluorescing. — Exhibiting the property of 
fluorescence. 

Flush Box.— (See Box, Flush) 

Fluviograph. — An apparatus for electri- 
cally registering the varying height of water 
in a tidal stream or in the ocean ; or, in general, 
differences of water levels. 

Flux, Magnetic —The number of 

lines of magnetic force that pass or flow 
through a magnetic circuit. 

The total number of lines of magnetic force 
in any magnetic field. 

The magnetic flux is also called the magnetic 
flow. 

A Committee of the American Institute of 
Electiical Engineers on " Units and Standards " 
propose! the following as the definition of mag- 
l.etic flux. 

" The magnetic flux through a surface bounded 
by a closed curve is the surface integral of mag- 
netic induction taken over the bounded surface, 
and when produced by a current is also equal to 
the line integral of the vector potential of the cur- 
rent taken round the boundary." 

" The uniform and unit time rate of change in 
flux through a closed electric circuit establishes 
unit electromotive force in the circuit." 

Fluxes range in present practical work from 
ioo to 100,000,000 C. G. S. lines, and the working 
units would perhaps prefix milli- and micro-. 

Flux of Magnetic Induction. — (See In- 
duction, Magnetic, Flux or Flow of) 

Flux or Flow of Magnetism. — (See Mag- 
netism, Flux or Flow of) 

Fly, Electric A wheel or other de- 
vice driven by the reaction of a connective 
discharge. (See Flyer, Electric. Convec- 
tion, Electric.) 



Fly.] 



234 



[Fur. 



-A wheel arranged 





Flyer, Electric — 

so as to be set into rotation by the escape of 
convection streams from its points when 
connected with a charged conductor. 

A wheel formed of 
light radial armsP, P, P, 
etc., shaped as shown in, 
Fig. 256, and capable of 
rotation on the vertical 
axis A, is set into rapid 
rotation when connected 
with the prime conduc- 
tor of a frictional or in- 
fluence machine, through 
the convection streams of 
air particles, which are Fig. 2s 6. Electric Flyer. 
shot off from the points or extremities of the 
radial arms. The wheel is driven by the reac- 
tion of these streams in a direction opposite to 
that of their escape. (See Discharge, Convective. ) 

Focus. — A point in front or back of a lens 
or mirror, where all the rays of light meet or 
seem to meet. (See Lens, Achromatic) 

Fog*, Electric A dense fog which 

occurs on rare occasions when there is an 
unusual quantity of free electricity in the 
atmosphere. 

Daring these electric fogs the free electricity of 
the atmosphere changes its polarity at frequent 
intervals. 

Following Horn of Pole Pieces of 
Dynamo-Electric Machine.— (See Horns, 
Following, of Pole Pieces of a Dynamo- 
Electric Machine) 

Foot-Candle.— (See Candle, Foot) 

Foot-Pound. — A unit of work. (See 
Work) 

The amount of work required to raise 1 
pound vertically through a distance of 1 foot. 

The same amount of work, viz., 3 foot-pounds, 
is done by raising I pound through a vertical 
distance of 3 feet, or 3 pounds through a verti- 
cal distance of I foot. 

Apart from air friction, the amount of work 
done in raising I pound through 1 foot, viz., 1 
foot-pound, is the same whether this work be 
done in one second or in one day. The potver, 
or the rate of doing work, is, however, very dif- 
ferent in the two cases. (See Power.) 

Force. — Any cause which changes or tends 



to change the condition of rest or motion of 
a body. 

Force, Centrifugal The force that 

is supposed to urge a rotating body directly 
away from the centre of rotation. 

If a stone be tied to a string and whirled around, 
and the string break, the stone will not fly off di- 
rectly away from the centre, but will move along 
the tangent to the point where it was when the 
string broke. 

The centrifugal force in reality is the force 
which is represented by the tension to which the 
string is subjected during this rotation. 

Force, Coercitive A name some- 
times applied to coercive force. (See Force t 
Coercive) 

Force, Coercive The power of re- 
sisting magnetization or demagnetization. 

Coercive force, in the sense of resisting demag- 
netization, is sometimes called ?nagnetic reten- 
tivity. 

Hardened steel possesses great coercive force;, 
that is, it is magnetized or demagnetized with 
difficulty. 

Soft iron possesses very feeble coercive force. 

It is on account of the feeble coercive force of 
the soft iron core of an electro-magnet that its 
main value depends, since it is thereby enabled to 
rapidly acquire its magnetization, on the comple- 
tion of a circuit through its coils, and to rapidly 
lose its magnetization on the opening of such 
circuit. 

Force, Contact A difference of elec- 
trostatic potential, produced by the contact of 
dissimilar metals. 

That a difference of potential is produced by 
the mere contact of dissimilar metals is now gen- 
erally recognized. Such a force is generally 
called the true contact force. (See Force, True 
Contact. ) 

Acco ding to Lodge, a true contact force has 
no existenje. There is no evidence, he thinks, 
of a peculiar electromotive force at the point of 
contact, but that the phenomena are due simply 
to the fact that the metals are immer?ed in air or 
oxygen, which is capable of combining with one 
of them, and that, therefore, the cause of the 
phenomena is the greater action, for instance, of 
the oxygen of the air on the zinc than on the 
copper. 



For.] 



235 



[For. 



According to this view, the voltaic effect is 
due not to the difference of potential between 
the zinc and copper, but to the difference of the 
action of the air or moisture. 

Force de Cheral or Cheval Tapenr. — 

The French term for horse-power. 

The force de cheval is equal to 75 kilogramme- 
metres per second, or 32,549 foot-pounds per 
minute. 

The English horse-power is equal to 33,000 
foot-pounds per minute. I force de cheval equals 
.98634 horse-power; 1 horse-power equals 1. 01 385 
force de cheval. — {Hering.) 



-The force developed 



Force, Electric — 

by electricity. 

This term is generally limited to the force of 
attraction or repulsion produced by an electro- 
static charge. 

Force, Electromotive The force 

starting electricity in motion, or tending to 
start electricity in motion. 

The force which moves or tends to move 
electricity. 

The term is an unfortunate one. Strictly speak- 
ing, electromotive force is not a force at all : 
at least, it is not a force in the Newtonian sense, 
where force is only that which acts on matter. 

The term electromotive force is generally writ- 
ten thus : E. M. F. 

The unit of electromotive force is the volt. 

When electric induction takes place, there 
results a change in the distribution of the thing 
called electricity, whereby a movement occurs that 
results in a positive and a negative charge. The 
cause which produces this movement is called the 
electromotive force. 

There is an unfortunate want of uniformity at 
present in the use of the term "electromotive 
force." By some, the electromotive force is re- 
garded as something which causes the difference 
of potential ; by others the electromotive force is 
regarded as being produced by the difference of 
potential; and, by still others, electromotive force 
is regarded as the entire electric moving cause 
produced by any source; while anything less than 
this is called by them potential difference. 

Those who regard the electromotive force as 
the cause which produces the potential difference 
look on the electromotive force as acting within 



the source and maintaining a potential difference 
at its terminals. 

Silvanus P. Thompson uses the term electro- 
motive force in his "Elementary Lessons in 
Electricity and Magnetism" as follows: "The 
term 'electromotive force' is employed to denote 
that which moves or tends to move electricity 
from one place to another. For brevity we some- 
times write it E. M. F. In this particular case it 
is obviously the result of difference of potential 
and proportional to it ; just as in water pipes, a 
difference in level produces a pressure, and the 
pressure produces a flow as soon as the tap is 
turned on, so difference of potential produces 
electromotive force, and electromotive force sets 
up a current as soon as a circuit is completed for 
the electricity to flow through." 

Mascart and Joubert, in their work on "Elec- 
tricity anl Magnetisn," Vol. I., say: "In all 
cases the difference of potential V^ — V 2 , may be 
considered as producing the motion of electrical 
masses ; it is often called the electromotive force." 

Maxwell, in his "Elementary Treatise on Elec- 
tricity," speaking of the potential differences 
which may be shown to exist at the terminals of 
a Daniell voltaic cell when on open circuit, says : 
"This difference of potential is called the electro- 
motive force of a Daniell cell." 

Balfour Stewart, in his " Electricity and Mag- 
netism, ' ' says : ' ' This difference of electric level 
we shall call E, and, indeed, it is merely a manner 
of expressing the cause of electromotive force." 

Prof. Fleming, in his "Short Lectures to Elec- 
trical Artisans," says: "The difference of elec- 
trical level or potential must be caused by some 
electromotive force acting in the conductor." 

Prof. Anthmy, in "A Review of Modern 
Electrical Theories," regards the potential dif- 
ference as due to electromotive force. He says : 
"Difference of potential results from a changed 
electrical distribution, an electrical strain, and 
represents the tendency to return to the state of 
equilibrium. Electromotive force is the some- 
thing from without that produced the electric 
strain." 

Hering, in his "Principles of Dynamo-Electric 
Machines," says : " Difference of potential is, as 
the name implies, the difference of electrical po- 
tential between any two points of a circuit, and 
may, therefore, be applied to that at the poles of 
a machine, battery or lamp, or at the ends of 
leads, or, in general, to any two points in a cir- 
cuit. The term 'electromotive lorce,' however, 



For.] 



236 



[For. 



applies only to the maximum difference ot potential 
which exists in the circuit, or, in other words, the 
total generated difference of potential." 

This last paragraph expresses the distinction 
"between the two terms as ordinarily used in con- 
nection with dynamos and batteries. 

Force, Electromotive, Absolute Unit of 
A unit of electromotive force ex- 
pressed in absolute or C. G. S. units. 

The one-hundred millionth part of a volt, 
since i volt equals 10 s C. G. S. units of elec- 
tromotive force. (See Units, Practical) 

Force, Electromotive, Average or Mean 

The sum of the values of a number of 

separate electromotive forces divided by their 
number. 

The square root of the mean square of the 
electromotive force of an alternating or vari- 
able current. 

When a wire in the armature of a dynamo- 
electric machine cuts the lines of magnetic force 
in the field of the machine, the ele tromotive 
force produced depends on the number of lines 
of force cut per second. This will vary for dif- 
ferent positions of the coil. The mean value of 
the varying electromotive forces between the 
brushes is the average electromotive force. 

Force, Electromotive, Back — A 

term sometimes used for counter electro- 
motive force. 

Counter electromotive force is the preferable 
term. (See Force, Electromotive, Counter.) 

Force, Electromotive, Counter 

An opposed or reverse electromotive force, 
which tends to cause a current in the oppo- 
site direction to that actually produced by 
the source. 

In an electric motor, an electromotive force 
contrary to that produced by the current 
which drives the motor, and which is pro- 
portional to the velocity attained by the 
motor. 

Counter electromotive force acts to diminish 
the current in the same manner as a resistance 
would, and is therefore sometimes called spurious 
resistance i 1 order to distinguish it from an ohmic 
or true resistance . 

Counter electromotive force is sometimes ex- 
pressed in ohms, though it is not a true ohmic 
resistance. (See Resistance, Spurious.) 



The counter electromotive force of a voltaic 
battery is due to the polarization of the cells. 
Since this force is due to the current in the cell, it 
can never exceed such current or reverse its direc- 
tion. It may, however, equal it and thus stop its 
flow. (See Cell, Voltaic, Polarization oj '.) 

In a storage cell, the charging current produces 
an electromotive force counter to itself, which, as 
in a motor, is a true measure of the energy stored 
in the cell. Economy requires that the electro- 
motive force of the charging current should be as 
little as possible greater than that of the counter 
electromotive force of the cell it is charging. 

In a voltaic arc a counter electromot.ve force is 
believed to be set up by polarization. 

Force, Electromotive, Counter, of Con- 

vective Discharge Resistance to the 

passage of an electric discharge through a 
high vacuum, somewhat of the nature of a 
counter electromotive force. 

The resistance t > the passage of convecive dis- 
charges, therefore, is due to the following causes: 

(i.) True ohmic resistance. 

(2.) Counter electromotive force. 

Force, Electromotive, Counter, of Mutual 

Induction The counter electromotive 

force produced by the mutual induction of 
the primary and secondary circuits on each 
other. 

Force, Electromotive, Counter, of Self- 
induction That part of the impressed 

electromotive force which is producing, or 
which tends to produce, at any instant a 
change in the current strength. 

Force, Electromotive, Counter, of Self- 
induction of the Primary A counter 

electromotive force produced in the primary 
circuit of an induction coil by the action 
thereon of a simple periodic electromotive 
force. 

The counter electromotive force produced 
in the primary circuit of an induction coil by 
the application of a simple periodic impressed 
electromotive force to the primary circuit. 

Force, Electromotive, Counter, of Self- 
induction of the Secondary — A 

counter electromotive force produced in the 
secondary by the periodic variations in the 
effective electromotive force in the secondary. 



For.] 



237 



[For 



Force, Electromotiye, Direct 



—An 

electromotive force acting in the same direc- 
tion as another electromotive force already 
existing. 

The term direct electromotive force is em- 
ployed in contradistinction to counter electromo- 
tive force. (See Force, Electromotive, Counter. ) 

Force, Electromotive, Effective 

The difference between the direct and the 
counter electromotive force. 

Force, Electromotive, Effective, of Sec- 
ondary The difference between the 

direct and the counter electromotive force in 
the secondary of an induction coil. 

Force, Electromotive, Generated by Dy- 
namo-Electric Machine, Method of Increas- 
ing* The electromotive force of a dy- 
namo-electric machine may be increased in 
the following ways, viz : 

(i.) By increasing its speed of rotation. 

(2.) By increasing the strength of the magnetic 
field in which the armature rotates. 

(3.) By increasing the size of the field through 
which the armature passes in unit time, the in- 
tensity remaining the same. 

(4.) By increasing the number of armature 
windings, i. <?., by making successive parts of the 
same wire pass simultaneously through the field. 

Force, Electromotive, Impressed 

The electromotive force acting on any cir- 
cuit to produce a current therein. 

The impressed electromotive force may be re- 
garded as producing two parts, viz. : The effective 
electromotive force and the counter electromotive 
force. 

Force, Electromotive, Inductive 

A term sometimes used in place of counter 
electromotive force of self-induction. 

Force, Electromotive, Inverse — 



—An 

electromotive force which acts in the oppo- 
site direction to another electromotive force 
already existing. (See Force, Electro?notzve, 
Counter.) 

Force, Electromotive, Motor A 

term proposed by F. J. Sprague for the coun- 
ter electromotive force of an electric motor. 
(See Force, Electromotive, Counter}) 

This term was propose! by Sprague as express- 



ing the necessity for the existence of a counter 
electromotive force in an electric motor, in order 
to permit it to utilize the energy of the electric 
current which drives it. 

Force, Electromotive, of Induction 

— The electromotive force developed by any 
inductive action. 

In a coil of wire undergoing induction, the 
value of the induced electromotive force does not 
depend in any manner on the nature of the ma- 
terial of which the coil is composed. 

It has been shown: 

(1.) That the electromotive force of induction is 
independent of the width, thickness or material of 
the wire windings. — {Far a day.) 

(2.) That it is dependent on the form of the 
conductor, and the character of the change it ex- 
periences as regards the magnetic induction which 
takes place through it. 

Since any increase in the strength of a current 
flowing through a coiled circuii, pioduces a coun- 
ter electromotive force, which opposes the electro- 
motive force producing the current, it is clear 
that the impressed electromotive force must do 
work against this counter electromotive force all 
the time the current strength is increasing. 

The movement of a circuit of a given length 
through a given field with a given velocity pro- 
duces the same electromotive force whether the 
circuit be formed of conducting material or non- 
conducting material, or consists of an electrolyte. 

Force, Electromotive, of Secondary or 

Storage Cell, Time-Fall of A gradual 

decrease in the potential difference of a stor- 
age battery observed during the discharge of 
the same. 

When a secondary or storage battery is first 
discharged, a slight decrease of its potential dif- 
ference takes place and a po'ential difference of a 
slightly decreased value is maintained nearly con- 
stant during a protracted period of disdiarge. 

Force, Electromotive, of Secondary or 

Storage Cell, Time-Rise of A gradual 

increase in the potential difference of a 
secondary or storage cell observed on begin- 
ning the discharge after a prolonged rest. 

When a secondary or storage cell is discharged 
and then given a prolonged rest by opening its 
circuit, a gradual but decided rise in its potential 
difference is observed on again beginning its dis- 
charge. 



For. 



233 



[For. 



Force, Electromotive, Photo An 

electromotive force produced by the action of 
light on selenium. (See Cell, Selenium.) 

Force, Electromotive, Reacting Induc- 
tive, of the Primary Circuit The back 

or counter electromotive force produced in the 
primary circuit by the current set up by in- 
duction in the secondary. 

Force, Electromotive, Secondary Im- 
pressed An electromotive force pro- 
duced in the secondary coil or circuit by a 
periodic electromotive force impressed on the 
primary. 

Force, Electromotive, Simple-Periodic 

An electromotive force which varies 

in such manner as to produce a simple 
periodic current, or an electromotive force the 
variations of which can be correctly repre- 
sented by a simple-periodic curve. 

Force, Electromotive, Thermo An 

electromotive force, or difference of potential, 
produced by differences of temperature 
acting at thermo-electric junctions. 

Force, Electromotive, Transverse 

An electromotive force excited by a mag- 
netic field in a substance in which electric 
displacement is occurring. 

It is to a transverse electromotive force that the 
Hall effect is due. (See Effect, Hall.) 

Force, Electromotive, Zigzag An 

electromotive force, the curve of which would 
have the general form of a zigzag. 

Force, Electrostatic The force pro- 
ducing the attractions or repulsions of charged 
bodies. 

Force, Electrostatic, Lines of 

Lines of force produced in the neighborhood 
of a charged body by the presence of the 
charge. 

Lines extending in the direction in which 
the force of electrostatic attraction or repul- 
sion acts. 

An insulated charged conductor produces 
around it an electrostatic field, in a manner some- 
what similar to the magnetic field produced by 
a magnet or an electric current. (See Field, 
Electrostatic. ) 



Lines of electrostatic force pass through dielec- 
trics. Whether the force acts to produce electro- 
static induction, by means of a polarization of the 
dielectric, or by means of a tension set up in the 
substance of the dielectric, is not known. 

Force, Electrostatic, Lines of, Assumed 

Flow of A mathematical conception in 

which the phenomena of electricity are com- 
pared with the similar phenomena of heat. 

In heat no flow of heat occurs over isothermal 
surfaces, or surfaces at the same temperature. 
Between different isothermal surfaces, the flow 
will vary with the power of heat conduction. In 
electricity, no flow occurs over equipotential sur- 
faces. Specific inductive capacity corresponds to 
heat conductivity, and the lines of force to the 
lines of heat conduction. (See Capacity, Specific 
Inductive.) 

Force, Lines of, Contraction of 

A decrease that occurs in the length of the 
circular lines of force that surround a circuit 
through which an electric current is passing, 
while the current is decreasing in intensity or 
strength. 

The contraction or decrease in the average 
diameter of the circular lines of force of an elec- 
tric circuit is similar to the expansion or growth 
of lines offeree, excepting that the movement is 
one of decrease in diameter, and takes place in 
the opposite direction, i. e., towards the circuit, 
instead of away from it. (See Force, Lines of,. 
Growth or Expansion of.) 

Force, Lines of, Cutting- Passing a 

conductor through lines of magnetic force, so 
as to cut or intersect them. 

The cutting of lines of magnetic force produces 
differences of potential. This is true whether the 
conductor moves through a stationary field or 
whether the field itself moves through the 
stationary conductor, so that the lines of force and 
the conductor cut one another. This cut.ing is 
mutual. Each line of force cuts and is cut by the 
circuit. Since all lines of force form closed-cir- 
cuits or paths, the cutting of the circuit by the 
lines of force, or the reverse, forms a link or chain, 
and the cutting takes place at the moment of 
linking or unlinking, i. e., of cutting. 

Force, Lines of, Diffusion of The 

deflection of the lines of magnetic force from 



For.] 



239 



[For. 



their ordinary position, between the poles 
that produce them. 

Force, Lines of, Direction of The 

direction in which it is assumed that the lines 
of magnetic force pass. 

It is generally agreed to consider the lines of 
magnetic force as coming out of the north pole of 
a magnet and passing into its south pole, as 
shown in Fig. 257. 




Fig. 257. Direction of Lines of Force. 

This is sometimes called the positive direction 
of the lines of force and agrees in general with the 
direction in which the electric current is assumed 
to flow, which is from the positive to the nega- 
tive. That is to say, the lines of magnetic force 
are assumed to flow or pass out of the north pole 
and into the south pole of a magnet. Of course 
there is no direct evidence of any flow, or of any 
particular dire:tion characterizing the lines of 
force. (See Field, Magnetic.) 

The lines of electrostatic force are assumed to 
pass out of a positively charged surface and into 
a negatively charged surface. 

Force, Lines of, Growth or Expansion of 

The increase in the length of path 

through which lines of force pass, consequent 
on an increase in the strength of the mag- 
netization of a magnet, or on an increase in 
the strength of the magnetizing current. 

The circular lines of force which surround a con- 
ductor through which a current is flowing, may be 
regarded as starting from the surface of the con- 
ductor and growing in size as they spread out- 
wards, at the same time new lines of force being 
formed in their places. This action continues while 
the strength of the current is increasing, somewhat 
like the series of concentric wives which are 
formed on the surface of water, when a stone is 
dropped into it. 

In their growth or expansion outwards from 
the conductor, if the lines of force cut or pass 
through neighboring conductors, they produce 



therein differences of electric Dotential, capable, 
on being connected by a conductor, of produc- 
ing electric currents. 

Force, Lines of. Radiation of The 

passing of lines of force out of the north 
pole of a magnet or solenoid. 

In gross matter all lines of magnetic induction 
either pass through magnetized iron, or other 
paramagnetic substance which surrounds an 
electric circuit. Since lines of force pass through 
a vacuum, the ether which occupies such a space 
must also be regarded as permitting the passage 
of lines of force. 

Force, Loops of A term sometimes 

employed in the sense of lines of force. (See 
Force, Magnetic, Lines of.) 

The term "Lines of Force" is generally 
a I opted in place of Faraday's term -'Loops of 
Force." 

Force, Magnetic The force which 

causes the attractions or repulsions of mag- 
netic poles. 

Force, Magnetic, Line of Arbitra- 
rily a single line of magnetic force. 

Practically the lines of magnetic force 
which pass through a unit area of cross-sec- 
tion of a magnetic field of unit strength. 

Force, Magnetic, Lines of Lines 

extending in the direction in which the mag- 
netic force acts. 

Lines extending in the direction in which 
the force of magnetic attraction or repulsion 
acts. (See Field, Magnetic) 

Faraday regarded the lines of magnetic force as 
possessing tension along one direction. Lines of 
force act as if they were stretched elastic threads, 
possessed of the property of lengthening or short- 
ening, and of repelling one another. 

Force, Magnetic, Lines of, Conducting 
Power for A term employed by Fara- 
day for magnetic permeability. (See Perme- 
ability, Magnetic.) 

Force, Magnetic, Lines of, Positive 

Direction of — The direction in which 

a free north-seeking pole would move along 
the lines of force when placed in a magnetic 
field. 



For.] 



240 



[For. 



Force, Magnetic, Telluric —The 

earth's magnetic force. 

Force, Magneto-Motive The force 

that moves or drives the lines of magnetic 
force through a magnetic circuit against the 
magnetic resistance. 

A Committee of the American Institute of Elec- 
trical Engineers on "Units and Standards " pro- 
posed the following definition. 

The magneto-motive force in a magnetic cir- 
cuit is 47T multiplied by the flow of the current 
linked with that circuit. The magneto-motive 
iorce between two points connected by a line is 
the line integral of the magnetic force along that 
line. Difference of magnetic potential constitutes 
magneto-motive force. ' ' 

The same committee gave the electro -magnetic 
dimensional formula L,2 M* T -1 . 

The flow or flux of lines of magnetic force in 
any magnetic circuit is proportional to the mag- 
neto-motive force divided by the magnetic resist- 
ance ; or, expressing the law in the form of Ohm's 
law for current: 

,, ,. T71 Magneto-Motive Force 

Magnetic Flux = ^r^ — 

Reluctance. 

In this formula the word reluctance is used in 
place of magnetic resistance. In the case of an 
electro-magnet, the magneto-motive force is pro- 
portional to the strength of the current which flows 
and the number of times it circulates; or, more 
simply, is proportional to the number of ampere 
turns. (See Turns, Ampere.) 

Force, Magneto-Motive, Absolute Unit of 

— 47r multiplied by unit current of one 

turn. 

Force, Magneto-Motive, Practical Unit 

of A value of the magneto-motive force 

equal to \n multiplied by the amperes of one 
turn, or to ■& of the absolute unit. 

Force, Motor Electromotive — A 

term proposed by F. J. Sprague for the 
counter electromotive force of a motor. 

During the rotation of the armature of an 
electric motor in its field, a counter electromotive 
force is produced in its coils, which acts as a 
spurious resistance and opposes the flow or pass- 
age of the driving current through its coils. As 
the speed of ihe motor increases, this counter 
electromotive force increases and the strength of 
the driving current decreases until a certain 



maximum speed is reached, when, theoretically, 
no current passes. 

When a load is placed on the electric motor, 
the speed, and consequently the counter electro- 
motive force, is decreased and more driving cur- 
rent is permitted to pass. It was this considera- 
tion, viz. : that the load automatically regulates 
the current required to drive the motor, that led 
to the name motor- electromotive force. (See 
Force, Electromotive, Counter.) 

Force, Resolution of The separa- 
tion of a single force, acting with a given 
intensity in a given direction, into a number 
of separate forces 
acting in some other 
direction. 

Thus the force D B, 
Fig. 258, acting with 
the intensity and in the 
direction shown, may 
be resolved into two 
component forces, D 
E and D C, acting in the directions and having 
the intensities shown. The single force D B, has 
been resolved into two separate forces D E and 
CD. 

— A force or 




258. Resolution of 
Force. 



Force, True Contact — 

effect entirely distinGt from the voltaic effect, 
which exists at the points of contact be- 
tween two dissimilar metals. 

The truth of the existence of a true contact force 
at the junction of dissimilar metals is seen by the 
reversible heat effects observed, when a current 
of electricity is passed across a junction of two 
dissimilar metals. When the current is passed in 
one direction, an increase of temperature is pro- 
duced, but when passed in the opposite direction, 
a decrease of temperature. (See Effect, Peltier.) 

Hence there would appear to be a force existing 
at the junction, helping the electricity along in 
one direction, but opposing it in the opposite di- 
rection. In one direction the electricity does 
work and consumes its own energy in so doing. 
In the other direction it opposes the passage of 
the current, and there results a generation of 
heat. 



Force, Tubes of 



-Tubes bounded by 



lines of electrostatic or magnetic force. 

Lines of force never intersect one another. 
Hence a tube of force may be regarded as con- 



For.] 



241 



[*r. 



taining the same number of lines of force at any 
and every cross-section. 

Tubes of electrostatic force always terminate 
against equal quantities of positive a id negative 
electricity respectively. They terminate when 
they meet a conducting surface. 

The term tubes of force is somewhat mislead- 
ing, since such so-called tubes are in general 
cones rather than tubes. 

Force, Twisting- A term sometimes 

used for torque. (See Torque.) 

Force, Unit of A force which, act- 
ing for one second on a mass of one 
gramme, will give it a velocity of one centi- 
metre per second. 

Such a unit of force is called a dyne. (See 
Dyne.) 

Forces, Composition of Finding 

the direction and intensity of a single force 
which represents the total effect of two or 
more forces acting simultaneously on a body. 
(See Component .) 

Forces, Parallelogram of A paral- 
lelogram constructed about the two lines that 
represent the direction and intensity with 
which two forces are simultaneously acting 
on a body, in order to determine the direction 
and intensity of the resultant force with 
which it moves. 

If the two forces A C and A B, Fig. 259, simul- 
taneously act in the direc- B ! D 
tion of the arrows on a 
body at A, the direction 
and intensity of the re- 
sultant A D, is deter- Ffo-. 2JQ . Farallelo- 
mined by drawing C D gram of Forces. 
and B D, parallel respectively to A B and A C. 
The diagonal A D, of the parallelogram AC D B, 
thus produced, gives this resultant. (See Com- 
ponent.) 

Fork, Trolley The mechanism 

which mechanically connects the trolley wheel 
to the trolley pole. (See Trolley.) 

Forked Circuits. — (See Circuits, Forked) 

Forked Lightning. — (See Lightning, 
Forked.) 

Formal Inductance of Circuit.— (See In- 
ductance, Formal, of Circuit.) 




Forming Plates of Secondary or Stor- 
age Cells. — (See Plates of Secondary or Stor- 
age Cells, Forming of.) 

Formulae. — Mathematical expressions for 
some general rule, law, or principle. 

Formulas are of great assistance in science in 
expressing the relations which exist between cei 
tain forces or values, and the effects that result 
from their operations, since they enable us to ex 
press these relations in clear and concise forms. 

Thus in the formulation of Ohm's law: 

«? = i 

we see that the continuous current C, in any cir- 
cuit, is equal to the elec rormtive force E, divided 
by the resistance R. Again, we see that the cur- 
rent is directly proportional to the electromotive 
force, and inversely prop jrtional to the resistance. 

Formulae are usually written in the form of an 
equation and therefore contain the sign oi equality 
or =. 

Formulae, Photometric (See Pho- 
tometric Formula.) 

Foucault Currents.— (See Currents, Fou- 
cault.) 

Four- Way Splice Box.— (See Box, Splice, 
Four- Way) 

Frames, Sectional Plating Frames 

employed for so holding the objects to be 
plated that they shall receive a greater depth 
of deposit on certain portions of their surface 
than elsewhere. 

Sectional printing frames depend for their 
action on the fact that the portions receiving the 
greater depth of deposit are nearer one of the 
electrodes than the rest of the surface. 

Franklinic Electricity. — (See Elec- 
tricity, Franklinic.) 

Franklinization. — Electrization by means 
of a frictional or influence machine as distin- 
guished from faradization or electrization by 
means of an induction coil. 

This term is used only in medical electricity. 

Free Charge. — (See Charge, Free.) 
' Free Magnetic Pole.— (See Pole, Mag- 
netic, Free.) 

Frequency of Alternations. — (See Alter- 
nations, Frequency of ) 



FrL] 



242 



[Fun. 



Friction Brake.— (See Brake, Friction?) 
Frictional Electrical Machine. — (See 

Machine. Frictional Electric?) 
Frictional Electricity.— (See Electricity. 

Frictional?) 

Frog, Galvanoscopic The hind legs 

cf a recently killed frog employed as an elec- 
troscope or galvanoscope, by sending- an elec- 
tric current from the nerves to the muscles. 
(See Electroscope?) 

In 1786, Luigi Galvani made the observation 
that when the legs of a recently killed frog were 
touched by a metallic conductor connecting the 
nerves with the muscles, the legs were convulsed 
as though alive. He repeated this experiment 
and found the move- 
ments were more pro- 
nounced when two dis- 
similar metals, such as 
iron and copper, were 
employed in the manner 
shown in Fig. 260. 

The classic experi- 
ment created intense 
excitement in the scien- 
tific world, and Galvani 
at first believed that he 
had discovered the true vital fluid of the animal, 
but afterwards recognized it as electricity, which 
he believed to be obtained from the body of the 
animal. Volta claimed that the movements were 
due to electricity caused by the contact of dissimi- 
lar metals, and thus produced his famous voltaic 
pile. (See Pile, Voltaic.) 

Frog, Trolley The name given to 

the device employed in fastening or holding 
together the trolley wires at any point where 
the trolley wire branches, and properly guiding 
the trolley wheel along the trolley wire on the 
movement of the car over the track. 

Frog, Trolley, Right-Hand A trol- 
ley frog used at the point where the branch 
trolley wire leaves the main line on the right 
of the direction in which the car is moving. 

Frog, Trolley, Standard The trol- 
ley frog used at the point where two branch 
lines make equally converging angles to the 
main line. 

Frog, Trolley, Three- Way A trol- 




Fig. 260. Galvanoscopic 
Frog. 



ley frog used where the line branches in three 
directions. 
Frying of Arc— (See Arc, Frying of) 
Fulgurite.— A tube of vitrified sand, be- 
lieved to be formed by a bolt of lightning. 

The fulgurite consists of an irregular shaped 
tube of glass formed of sand which has been 
melted by the electric discharge. 

Full Contact— (See Contact, Metallic) 

Fuller's Mercury Bichromate Voltaic 
Cell. — (See Cell, Voltaic, Fuller s Mercury 
Bickro?7iate.) 

Fulminate.— The name of a class of highly 
explosive compounds. 

Fulminating gold, silver and mercury are 
highly explosive substances. Fulminates are 
employed in percussion caps. 

Function, Trigonometrical Cer- 
tain quantities, the values of which are de- 
pendent on the length of the arcs subtended 
by angles, which are taken for the measures 
of the arcs or angles instead of the arcs 
themselves. 

The trigonometrical functions are the sine, the 
co-sine, the tangent, the co-tangent, the secant 
and the co-secant. 

These are generally abbreviated thus, viz. : sin. , 
cos., tan., cot., sec. and co-sec. 

The sine of an angle or arc is the perpendic- 
ular distance from one L C 
extremity of the arc to 
the diameter passing 
through the other ex- 
tremity. 

Thus in Fig. 261 B D,' G 
is the sine of the angle 
BOA, or of the arc, 
B A. 

The co-sine of an an - 
gleor arc is that part of Fig. 261. Trigonometri- 
the diameter which lies cal Functions. 

between the foot of the sine and the centre. Thus, 
D O, is the co-sine of the angle B O A, or of the 
arc B A. 

The co-sine of an arc is equal to the sine of its 
complement. Thus E O B, or B E, the comple- 
ment of B A, has for its sine I B, which is equal 
to O D. (See Angle, Complement of ".) 

If the arc is greater than a right angle, or 90 




Fun.] 



243 



[Fus. 



degrees, such, for instance, as the angle TOG, 
or the arc B E F G, B D, is its sine. This is also 
the sine of B O A, or B A, which is the supple- 
ment of T O G, or B E F G. Hence the sine of 
an arc is equal to the sine of its supplement. 

The same is true of the co-sine. 

The tangent of an angle or arc is a straight 
line touching the arc at one extremity, drawn 
perpendicular to the diameter at that end of the 
arc, and limited by a straight line connecting the 
centre of the circle and the other end of the arc. 
Thus C A, is the tangent of the angle B O A, or 
the arc B A. 

The co-tangent of an angle or arc is equal to 
the tangent of its complement. Thus E T, is the 
co-tangent of the angle B O A, or the arc B A. 

The tangent of an angle or arc is equal to the 
tangent of its supplement. Thus A C, is the tan- 
gent of the angle B O A, or the arc B A. It is 
also equal to the tangent of the angle B O G, or 
the arc BEFG. the correspo .ding supplement of 
the angle B O A, or the arc B A. 

The secant of an angle or arc is the straight 
line drawn from the centre of the circle through 
one extremity of the arc and limited by the tan- 
gent passing through the other extremity. Thus 
O C, is the secant of the angle B O A, or of the 
arc B A. 

The secant of an angle or arc is equal to the 
secant otits supplement. 

The co-secant of an angle or arc is equal to 
the secant of its complement. 

Thus O T, is the co-secant of the angle BOA, 
or of the arc B A. 

It will be observed that the co-sine, the co- 
tangent and the co-secant are respectively the 
sine, tangent and secant of the complement of 
the arc, or in other words, the complement-sine, 
the complement-tangent and the complement- 
secant. 

Fundamental Units. — (See Units, Funda- 
mental.) 

Furnace, Electric — A furnace in 

which heat generated electrically is employed 
for the purpose of effecting difficult fusions 
for the extraction of metals from their ores, 
or for other metallurgical operations. 

In electric furnaces, the heat is derived either 
from electric incandescence or from the voltaic arc. 
"The latter form is frequently adopted. 

The substance to be treated is exposed directly 



to the voltaic arc. In some forms of furnace the 
crushed ore is permitted to fall through the arc, 
and the melted matter received in a suitable ves- 
sel in which the separation of the substances so 
formed is afterwards completed. In other forms 
of furnace, the ore is placed between two elec- 
trodes of carbon or other refractory substance, 
between which a powerful current is passed. In 
the Cowles furnace, when aluminium is reduced, 
molten copper forms an alloy with the aluminium 
as soon as separated. 

Very numerous applications of electricity to 
furnace operations have been made. 

Fuse Block.— (See Block, Fuse.) 

Fuse Board.— (See Board, Fuse.) 

Fuse Box.— (See Box, Fuse.) 

Fuse, Branch —A safety fuse or 

strip placed in a branch circuit. (See Fuse, 
Safety.) 

Fuse, Converter —A safety fuse con- 
nected with the circuit of. a converter or 
transformer. 

Fuse, Electric A device for elec- 
trically igniting a charge of powder. 

Electric fuses are employed both in blasting 
operations and for firing cannon. 

Electric fuses are operated either by means of 
the direct spark, or by the incandescence of a 
thin wire placed in the circuit. They are there- 
fore either high tension, or low tension fuses. 

The advantages of an electric fuse consist in 
the fact that its use permits the simultane jus fir- 
ing of a number of charges in a mining operation, 
thus obtaining a greater effect from the explosion. 
A fulminate of merciry is frequently employed 
in connection with some forms of electric fuses. 

Fuse, Electric, Hig'h-Tension A 



fuse that is ignited by the heating power of 
an electric spark. 

High-tension fuses, therefore, require a high 
electromotive force. This is obtained either by 
means of induction coils or by some form of 
electrostatic induction machine. 

Fuse, Electric, Low-Tension A 

fuse that is ignited by heating a wire to incan- 
descence by the passage through it of an 
electric current. 
Fuse, Electric, Stratliam's A form 



Fas.] 



2U 



[Gal 



of fuse, in which the ignition is effected by the 
electric spark, is shown in Fig. 262. 

The spark passes through a break A B, in the in- 
sulated leads D. Since gunpow- 
der is not readily ignited by an 
electric spark, a peculiar priming 
material is employed at A B, in the 
place of ordinary powder. 

Fuse Links. — (See Links, 
Fuse.) 
Fuse, Magazine — A 

safety fuse so arranged as to 
readily permit the replacement 
of the fuse when burned out. 

A spool contains a coil of fuse 
wire. In order to release the 
burned-out fuse, a wedge-shaped 
device is provided to open the clamps that hold 
the fuse strip to release the portions of burned- 
out fuse left, and connection with the fuse strip 
is severed while the attachment of the new strip 
is being made. 

Fuse, Main A safety fuse or strip 

placed in a main circuit. (See Fuse, Safety.) 

Fuse, Platinum A thin platinum 

wire rendered incandescent by the passage of 
an electric current and employed for the igni- 
tion of a charge of powder. (See Fuse, 
Electric?) 

Fuse, Safety A strip, plate or bar 

of lead, or some readily fusible alloy, that au- 
tomatically breaks the circuit in which it is 
placed on the passage of a current of suf- 



Fig. 262. 

Strut ham's 

Fuse. 



ficient power to fuse such strip, plate or bar^ 
when such current would endanger the safety 
of other parts of the circuit. 

Safety fuses are often called safety strips or 
safety plugs. 

Safety fuses are made of alloys of lead, and 
are placed in boxes lined with non-combustible 
material in order to prevent fires from the molten 
metal. 

Fig. 263 shows a fusible strip F, connected with 
leads L, L. Safety fuses are placed on all branch 
circuits, and are made of sizes proportionate to* 
the number of lamps they guard. 




Fig. 263. Safety Fuse. 

Since incandescent lamps are generally placed 
in the circuit in multiple- arc, or in multiple-series, 
one or more of the circuits can be opened by the 
fusion of the plug without interfering with the 
continuity of the rest of the circuits. In series 
circuits, however, such as arc -light circuits, when 
a lamp is cut out, a short circuit or path around 
it must be provided in order to avoid the extin- 
guishing of the rest of the lights. 

Fuse Wire. — (See Wire, Fuse.) 

Fusible Plug. — A term commonly applied, 
to a safety plug. (See Fuse, Safety 



G 



Gains. — The spaces cut in the faces of 
telegraph poles for the support or placing of 
the cross arms. 

Galvanic Battery. — (See Battery, Gal- 
vanic?) 

Galvanic Cell. — (See Cell, Voltaic) 

Galvanic Circle. — (See Circle, Galvanic.) 

Galvanic Circuit. — (See Circuit, Gal- 
vanic) 



Galvanic Dosage. — (See Dosage, Gal- 
vanic) 

Galvanic Electricity. — (See Electricity, 
Galvanic) 

Galvanic Excitability of Nerve or Mus- 
cular Fibre. — (See Excitability, Electric y 
of Nerve or Muscular Fibre) 

Galvanic Irritability. — (See Irritability y 
Galvanic) 



tial. 



245 



[GaK 



Galvanic Multiplier. — (See Multiplier, 
Galvanic?) 

Galvanic Polarization. — (See Polariza- 
tion, Galvanic.) 

Galvanic Taste. — (See Taste, Galvanic?) 

Galvanism. — A term sometimes employed 
to express the effects produced by voltaic 
electricity. 

Galvanization, Central A variety 

of general galvanization in which the kathode 
is placed on the epigastrium and the anode 
moved over the body. 

Galvanization, Electro-Metallurgical 
The process of covering any conduc- 
tive surface with a metallic coating by elec- 
trolytic deposition, such, for example, as the 
thin copper coating deposited on the carbon 
pencils or electrodes used in systems of arc 
lighting. 

The term is borrowed from the French, in 
which it has the above signification. It is prefer- 
ably replaced by the term electro-plating. (See 
Plating, Electro.) 

The term galvanization is never correctly ap- 
plied to the process for covering iron with zinc or 
other metal by dipping the same in a bath of 
molten metal. 

Galvanization, Electro-Therapeutical 

In electro-therapeutics, the effects 

produced on nervous or muscular tissue by 
the passage of a voltaic current. 

Galvanization, General A method 

of applying a current therapeutically by the 
use of electrodes of sufficient size to direct 
the current through practically the entire 
body. 

Galvanization, Labile — A term 

employed in electro-therapeutics, in contradis- 
tinction to stabile galvanization, to designate 
the method of applying the current by keep- 
ing one electrode at rest in firm contact with 
one part of the body, and connecting the other 
electrode to a sponge which is moved over 
the parts of the body that are to be treated. 

Galvanization, Local The applica- 
tion of galvanization to parts or organs of the 
body in contradistinction to general galvani- 
zation. 



Galvanization, Stabile A term 

employed in electro-therapeutics in which the 
current is caused to pass continuously and 
steadily through the portions of the body un- 
dergoing galvanization. 

In stabile galvanization, the current is applied 
to and removed from the body gradually, in order 
to avoid shocks at the beginning and end of the 
application. 

Galvanized Iron. — (See Iron, Galvan- 
ized.) 

Galvano. — A word sometimes used in 
France in place of the word electro, to signify 
an article reproduced in copper by electro- 
metallurgy, especially an electrotype or wood- 
cut. 

Galvano-Causty. — (See Causty, Galvano.) 

Galvano-Cautery. — (See Cautery, Gal- 
vano) 
Galvano-Cautery, Chemical — A 

term sometimes applied to electro puncture 
or the application of electrolysis to the treat- 
ment of diseased growths. (See Cautery, 
Electric. Puncture, Electro?) 

The term chemical galvano-cautery would ap- 
pear to be poorly chosen, as it would imply the 
existence of a cautery action, which in point of 
fact does not exist. 

Galvano-Faradization. — In electro-thera- 
peutics, the simultaneous excitation of a nerve 
or muscle by both a voltaic and a faradic cur- 
rent. 

Galvano-Magnet. — A term sometimes used 
for electro-magnetic. 

Electro -magnetic is by far the preferable term, 
and is almost universally employed in the United 
States. 

Galvanometer. — An apparatus for meas- 
uring the strength of an electric current by 
the deflection of a magnetic needle. 

The galvanometer depends for its operation on 
the fact that a conductor, through which an elec- 
tric current is flowing, will deflect a magnetic 
needle placed near it. This deflection is due to 
the magnetic field caused by the current. (See 
Field, Magnetic, of an Electric Current.) 

This action of the current was first discovered 
by Oersted. A wire conveying a current in the 



Gal 



246 



[Gal. 



direction shown by the straight arrow, Fig. 264, 
or from + to — , will deflect a magnetic needle in 
the direction shown by the curved arrows. 

The following rules show the direction of the 




Fig. 264. Oersted's Experiment. 

deflection of a magnetic pole by an electrical cur- 
rent : 

(1.) Place the right hand on the conductor 
through which the current is flowing, with the 
palm facing the north pole, and with the fingers 
pointing in the direction of the current. The 
thumb will indicate the direction in which the 
north pole tends to move. 

(2.) Suppose an ordinary corkscrew so placed 
along the conductor, through which a current of 
electricity is passing, that when twisted, it will 
move in the direction of the current. The han- 
dle will then turn in the direction in which the 
north pole of the magnet tends to move. 

(3.) Imagine one swimming along the con- 
ductor in the direction of the current and facing 
the magnet. The north pole will tend to move 
towards the left hand of the swimmer. 

Prof. Forbes has shown that the direction of 
the deflection of a magnet by a current is such 
A 6 C 




Fig. 265. Amplre's Apparatus. 

that if the magnet were flexible, it would wrap 
itself round the current. 

If the wire be bent in the form of a hollow rec- 
tangle F, D, E, G, Fig. 265, and the needle, M, 



be placed inside the circuit, the upper and lower 
branches of the current will deflect the needle in 
the same direction, and the effect of the current 
will thus be multiplied. Mercury cups are pro- 
vided at A, B and C, for a ready change in the 
direction of the current. (See Needle, Astatic.') 

This principle of the multiplication of the de- 
flecting power of a current was first applied to gal- 
vanometers by Schweigger, who used a number of 
turns of insulated wire for the purpose of obtain- 
ing a greater deflection of the needle. He called 
such a device a multiplier. In extremely sensi- 
tive galvanometers, very many turns of wire are 
employed, in some cases amounting to many 
thousands. Such galvanometers are of high re- 
sistance. Others, of low resistance, often con- 
sist of a single turn of wire and a:e used in the 
direct measurement of large currents. 

A Schweigger' s multiplier or coil C, C, of 
many turns of insulated wire, is shown in Fig. 266. 
The action of such a coil on the needle M, is com- 
paratively great, even when the current is small. 




Fig. 266. Schweigger' s Midtiplier. 

In the case of any galvanometer, when no cur- 
rent is passing, the needle, when at rest, should in 
general occupy a position parallel to the plane of 
the coil. On the passage of the current, the 
needle tends to place itself in a position at right 
angles to the direction of the current, or to the 
length of the conducting wire in the coil. The 
strength of the current passing is determined by 
observing the amount of this deflection as meas- 
ured in degrees on a graduated circle over which 
the needle moves. 

The needle is deflected by the current from a 
position of rest, either in the earth's magnetic 
field or in a field obtained from a permanent or 
an electro magnet. In the first case, when in use 
to measure a current, the plane of the galvanom- 
eter coils must coincide with the planes of the 
magnetic meridian. In the other case, the instru- 



Gal.] 



247 



[Gal. 



ment may be nsed in any position in which the 
needle is free to move. 

Galvanometers assume a variety of forms ac- 
cording either to the purposes for which they are 
employed, or to the manner in which their deflec- 
tions are valued. 

Galvanometer, Absolute A galva- 
nometer whose constant can be calculated 
with an absolute calibration. (See Calibra- 
tion, Absolute?) 

Such a galvanometer is called absolute because 
if the dimensions of its coil and needle are known, 
the current can be determined directly from the 
observed deflection of the needle. 

Galvanometer, Aperiodic A gal- 
vanometer the needle of which comes to its 
position without any oscillation. 

A dead-beat galvanometer. (See Galva- 
nometer, Dead-Beat.) 

Galvanometer, Astatic A galva- 
nometer, the needle of which is astatic. (See 
Needle, Astatic?) 

Nobili's astatic galvanometer is shown in Fig. 
267. The astatic needle, suspended by a fibre b, 
has its lower needle placed inside a coil, a, con- 
sisting of many turns of insulated wire, its upper 
needle moving over the graduated dial. The cur- 
rent to be measured is led into and from the 
■coil at the binding posts, x and y. 




Fig. 267. Astatic Galvanojneter. 

In this instrument, if small deflections only are 
employed, the deflections are sensibly propor- 
tional to the strength of the deflecting currents. 

Galvanometer, Ballistic A galva- 
nometer designed to measure the strength of 
currents that last but for a moment, such, for 
example, as the current caused by the dis- 
charge of a condenser. 



The quantity of electricity passing in any cir- 
cuit is equal to the current multiplied by the time. 
Since the current caused by the discharge of a 
condenser lasts but for a small time, during which 
it passes from zero to a maximum and back again 
to zero, the magnetic needle in a ballistic galva- 
nometer takes the form of a ballistic pendulum, 
i. e., it is given such a mass, and acquires such a 
slow motion, that its change of position does not 




Fig. 268. Ballistic Galvanometer. 

practically begin until the impulses have ceased 
to act. 

In the ballistic galvanometer of Siemens and 
Halske, the coils R, R, Fig. 268, have a bell- 
shaped magnet, M, suspended inside them by 
means cf an aluminium wire. The magnet is pro- 
vided with a mirror S, for measuring the deflec- 
tions. The bell-shaped magnet is shown in ele- 
vation at M, and in plane at n, s. 

In using the ballistic galvanometer, it is neces- 
sary to see that the needle is absolutely at rest be- 
fore the charge is sent through the coils. 

A form of ballistic galvanometer by Nalder is 
shown in Fig. 269. 

The ordinary form of compensating magnet 
is, in this galvanometer, replaced by the small mag- 
net A, capable of rotation in a horizontal plane, but 
incapable of being raised or lowered, as is usual 
in such magnets. This form of compensating mag- 
net possesses the advantage of being able to alter 
the direction of the field on the needle system, 



Gal.] 



248 



[Gal. 



without considerably altering its intensity. When 
the galvanometer is for ready use the magnet A, is 
turned until the needle is brought to zero. The 




Fig. 26g. Haider's Galvanometer. 
combined field of earth and magnet A, are then 
brought to the degree of sensitiveness required 




Fig. 2 -jo. Nalder s Galvanometer. 

by rotating magnet B, on its shaft, or altering 
its distance from the needle. In order to insure 
ease in replacing the fibre, the front coil is hinged 
as shown. The fibre D, is supported on E, one 
end of which it is free to turn, so as to permit of 
the removal of torsion; D, being twisted can be 
raised or lowered at E. The needle system with 
heavy bell-shaped magnet is shown in Fig. 270. 

Galvanometer, Combined Tangent and 

Sine A galvanometer furnished with 

two magnetic needles of different lengths. 
The small needle is used for tangent measure- 
ments, and the long needle for sine measure- 
ments. 

Galvanometer Constant. — (See Constant, 
Galvanometer?) 

Galvanometer, Dead-Beat A gal- 
vanometer, the needle of which comes quickly 
to rest, instead of swinging repeatedly to-and- 
fro. (See Damping) 

Galvanometer, Deprez-D'Arsonval 

— A form of dead-beat galvanometer. 

The movable part of the Deprez-D'Arsonval 
galvanometer consists of a light rectangular coil 



C, Fig. 271, of many turns of wire, supported 
by two silver wires H J and D E, between the 
poles of a strong permanent horseshoe magnet 
A A. The position of 
the coil may be altered 
as to height by screws 
at H and E. The sup- 
porting wires, prevent 
by their torsion the 
swinging of the coil, as 
does also the cylinder 
of soft iron B, placed 
inside the coil, and sup- 
ported independently 
of it. The movements 
of the coil are observed 
by means of a spot of 
light reflected from a 
mirror J, attached to 
the wire H J. 




Fig. 271. Deprez-D'Arson- 
val Galvanometer. 



Galvanometer, Detector 



A form of 



galvanometer employed for rough testing 
work. 

A form of detector galvanometer is shown in 
Fig. 272. 




Fig. 2 J 2. Detector Galvanometer. 

Galvanometer, Differential A gal- 
vanometer containing two coils so wound as 
to tend to deflect the needle in opposite 
directions. 

The needle of a differential galvanometer shows 
no deflection when two equal currents are sent 
through the coils in opposite directions, since, 
under these conditions, each coil neutralizes the 
other's effects. Such instruments may be used 
in comparing resistances. The Wheatstone 
Bridge, however, in most cases, affords a prefer- 
able method for such purposes. (See Bridge \ 
Electric. ) 



Gal.] 



249 



[Gal. 



A form of differential galvanometer is shown in 
Fig. 273. 

Sometimes the current is so sent through the 
two coils, that each 
coil deflects the nee- 
dle in the same di- 
rection. In this case 
the instrument is no 
longer differential in 
action. 

If the magnetic 
needle, in such cases, 
is suspended at the 
exact centre of the 
line which joins the 
centres of the coils, 
the advantage is 
gained by obtaining 
a field of more nearly 
uniform intensity 
around the needle. 




Differential Galva- 
nometer. 



Galvanometer, Figure of Merit of 

The reciprocal of the current required to pro- 
duce a deflection of the galvanometer needle 
through one degree of the scale. 

The smaller the current required to produce a 
deflection of one degree, the greater the figure 
of merit, or the greater the sensitiveness of the 
galvanometer. 

Galvanometer, Marine A galva- 
nometer devised by Sir William Thomson for 
use on steamships where the motion of mag- 
netized masses of iron would seriously disturb 
the needles of ordinary instruments. 

An unscreened needle would be so much af- 
fected by the motion of the engines, the shaft and 
the screw, as to be useless for galvanometric 
measurement. 

The needle of the marine galvanometer is 
shielded or cut off from the extraneous fields so 
produced, by the use of a magnetic screen or 
shield, consisting of an iron box with thick sides, 
inside of which the instrument is placed. 

The needle is suspended by means of a silk 
fibre attached both above and below, in line with 
the centre of gravity of the needle. In this man- 
ner, the oscillations of the ship do not affect the 
needle. 

Galvanometer, Mirror A galva- 
nometer in which, instead of reading the de- 
flections of the needle directly by its move- 



ments over a graduated circle, they are read 
by the movements of a spot of light reflected 
from a mirror attached to the needle. 

This spot of light moves over a graduated 
scale, or its movements are observed by means of 
a telescope. 




Fig. 2 J 4. Mirror Galvanometer. 

A form of mirror galvanometer designed by Sir 
William Thomson is shown in Fig. 274. The 
needle is attached directly to the back of a light, 
silvered glass mirror, and consists of several small 
magnets made of pieces of a watch spring. The 
needle and mirror are suspended by a single silk 
fibre and are placed inside the coil. A compen- 
sating magnet N S, movable on a vertical axis, is 
used to vary the sensitiveness of the instrument. 
The lamp L, placed back of a slot in a wide 
screen, throws a pencil of light on the mirror Q, 
from which it is reflected to the scale K. 

A form of lamp and scale with slot for light is 
shown in Fig. 275. 




Fig. 275. Galvanometer Lamp and Scale. 

Galvanometer, Potential A term 

sometimes applied to a voltmeter. (See 
Voltmeter?) 

Galvanometer, Reflecting 1 A term 

sometimes applied to a mirror galvanometer, 
(See Galvanometer, Mirror?) 



Gal.] 



250 



[Gal, 



Galvanometer, Sensibility of The 

readiness and extent to which the needle of a 
galvanometer responds to the passage of an 
electric current through its coils. (See Gal- 
vanometer^) 

Galvanonieter-Shunt. — (See Shunt, Gal- 
vanometer.') 

Galvanometer, Sine — A galva- 
nometer in which a vertical coil is movable 
around a vertical axis, so that it can be made to 
follow the magnetic needle in its deflections. 

In the sine galvanometer, the coil is moved so 
as to follow the needle until it is parallel with the 
coil. Under these circumstances, the strength 
of the deflecting currents in any two different 
cases is proportional to the sines of the angles of 
deflection. 

A form of sine galvanometer is shown in Fig. 
276. The vertical wire coil is seen at M. A 
needle of any length less than the diameter of the 
coil M, moves over the graduated circle N. The 
coil M, is movable over the graduated horizontal 
circle H, by which the amount of the movement 




Sine Galvanometer. 



necessary to bring the needle to zero is measured. 
The current strength is proportional to the sine 
of the angle measured on this circle, through 
which it is necessary to move the coil M, from its 



position when the needle is at rest in the plane of 
the earth's magnetic meridian, until the needle 
is not further deflected by the current, although 
parallel to the coil M. 

Galvanometer, Tangent — 



— An instru- 
ment in which the deflecting coil consists of 
a coil of wire within which is placed a needle 
very short in proportion to the diameter of 
the coil, and supported at the centre of the 
coil. 




Fig. 277. Tangent Galvanometer. 

A galvanometer acts as a tangent galvanometer 
only when the needle is very small as compared 
with the diameter of the coil. The length of the 
needle should be less than one-twelfth the diameter 
of the coil. 

A form of tangent galvanometer is shown in 
Fig. 277. The needle is supported at the exact 
centre of the coil C. 

Under these circumstances, the strengths of 
two different deflecting currents are proportional 
to the tangents of the angles of deflection. Tan- 
gent galvanometers are sometimes made with 
coils of wire containing many separate turns. 

Galvanometer, Tangent, Obach's — 

A form of galvanometer in which the deflect- 
ing coil, instead of being in a fixed vertical 
position, is movable about a horizontal axis, 
so as to decrease the delicacy of the instru- 
ment, and thus increase its range of work. 

Galvanometer, Torsion A galva- 
nometer in which the strength of the deflecting 
current is measured by the torsion exerted on 
the suspension system. 

A ball- shaped magnet, shown at the right of 
Fig. 278, is suspended by a thread and spiral. 



Gal.] 



251 



[Gal. 



spring between two coils of high resistance, 
placed parallel to each other in the positions 
shown. On the deflection of the magnet, by the 
current to be measured, the strength of the current 
is determined by the amount of the torsion re- 
quired to bring the magnet back to its zero point. 




Fig. 278. lorsion G dvanomete . 

The angle of torsion is measured on the horizontal 
scale at the top of the instrument. 

In the torsion galvanometer, unlike the electro- 
dynamometer, the action between the coils and the 
movable magnet is as the current strength causing 
the deflection. In the electro-dynamometer, 
since an increase of current in the deflecting coils 
also takes place in the deflected coil, the mutual 
action of the two is as the square of the current 
strength causing the deflection. 

Galvanometer, Upright A gal- 
vanometer, the needle of which moves in a 
vertical plane. (See Galva7iometer, Ver- 
tical. 

Galvanometer, Vertical A gal- 
vanometer the needle of which is capable of 
motion in a vertical plane only. 

In the vertical galvanometer, the north pole of 
the needle is weighted so that the needle as- 
sumes a vertical position when no current is pass- 
ing. In the form shown in Fig. 279, two needles 




Fig, 27 q. Vertical Galva- 
nometer. 



are sometimes employed, one of which is placed 
inside the coils C, C. 

The vertical galvanometer is not as sensitive as 
the ordinary forms. It is employed, however,, 
in various forms for an 
electric current indica- 
tor, or even for a 
rough current meas- 
urer. 

Galvanometer 
Voltmeter. — An in- 
strument devised by 
Sir William Thom- 
son, for the meas- 
urement of differ- 
ences of electric 
potential. 

This instrument is so arranged that by a single 
correction for the varying strength of the earth's 
field in any place, the results are read at once in 
volts. 

A coil of insulated wire shown at A, Fig. 280, 
has a resistance of over 5,000 ohms. A magnetic 
needle, formed of short parallel needles placed 
above one another, and called a magnetometer 
needle, is attached to a long but light aluminium 
index, moving over a graduated scale. A mova- 
ble, semi-circular magnet B, called the restoring 
magnet, is placed over the needle, and is used 
for varying the effect of the earth's field at any 
point. The sensitiveness of the instrument may 
be varied either by the restoring magnet or by 
sliding the magnetometer box nearer to or further 
away from the coil. 

The voltmeter galvanometer depends for its 
operation on the fact that when a galvanometer 
of sufficiently high resistance is introduced be- 




Fig. 280. Galv.inojneter Voltmeter. 

tween any two points in a circuit, the current that 
passes through it, and hence the deflection of its 
needle, is directly proportional to the difference 
of potential between such two points. 



Gal.] 



252 



[Gas. 



Galvanometers for the commercial measure- 
ments of currents assume a variety of forms. 
They are generally so constructed as to read off 
the amperes, volts, ohms, watts, etc., directly. 
They are called amperemeters or ammeters, volt- 
meters, ohmmeters, wattmeters, etc. For their 
fuller description reference should be had to 
standard works on electrical measurement. 

Galvanoinetric. — Of or pertaining to the 
galvanometer. (See Galvanometer) 

Galvanometrical. — Of or pertaining to the 

galvanometer. (See Galvanometer) 

Galvanonietrically. — In a galvanometric 
manner. 

Galvano-Plastics. — (See Plastics, Gal- 
vano) 

Galvanoplasty. — The art of galvano- 
plastics. (See Plastics, Galvano.) 

Galvano-Puncture. — (See Puncture, Gal- 
vano?) 

Galvanoscope. — A term sometimes im- 
properly employed in place of galvanometer. 

A galvanoscope, strictly speaking, is an instru- 
ment intended rather to show the exis ence of an 
electric current than to measure it in degrees. 
It may, however, be roughly calibrated, and then 
it differs from a galvanometer only in delicacy 
and accuracy. 

Galvano-Therapeutics. — A term some- 
times used for electro-therapeutics. 

Electro-therapeutics is by far the preferable 
term and is almost universally employed in the 
United States. 

Gap, Air A gap, or opening in 

a magnetic circuit containing air only. (See 
Gap, Air, Magnetic.) 

The air gap between two magnetic poles may 
be regarded as the space in which an armature 
acting as a magneto- receptive device is placed, 
which by the action upon it of the lines of mag- 
netic force passing through the gap has differ- 
ences of potential generated in its coils of insulated 



Gap, Air, Magnetic 



-A gap filled 



with air which exists in the opening at any 
part of a core of iron or other medium of high 
permeability. 

The space between the pole pieces and arma- 



ture core is called the air gap in dynamos or 
motors even though partly filled with copper con- 
ductors. It is also called the interference space. 

The gap or air space of an electro-magnet de- 
creases the strength of its magnetization be- 
cause — 

The increased reluctance of the air gap causes 
a decrease in the number of lines of magnetic 
force which pass through the magnetic circuit. 

Gap, Spark A gap forming part of 

a circuit between two opposing conductors, 
separated by air, or other similar dielectric 
which is closed by the formation of a spark 
only when a certain difference of potential 
is attained. 

Gap, Wire-Gauge — (See Gauge, 

Wire, Gap.) 

Gas-Battery . — (See Battery, Gas) 

Gas Burner, Argand, Plain-Pendant, 

Electric — (See Burner, Argand 

Electric, Plain-Pendant.) 

Gas Burner, Argand, Ratchet-Pendant, 
Electric (See Burner, Argand Elec- 
tric, Ratchet-Pendant) 

Gas Burner, Automatic Electric 

(See Bur?ier, Automatic Electric) 

Gas Burner, Plain-Pendant, Electric 
(See Burner, Plain-Pendant Elec- 
tric) 

Gas Burner, Ratchet-Pendant, Electric 
(See Burner, Ratchet-Pendant Elec- 
tric) 

Gas, Carbonic Acid A gaseous sub- 
stance formed by the union of one atom of 
carbon with two atoms of oxygen. 

Carbonic acid gas is formed during the com- 
bustion of carbon by a sufficient supply of air. 

Gas, Dielectric Density of A term 

sometimes emploved instead of dielectric 
strength of gas. (See Gas, Dielectric 
Strength of) 

Gas, Dielectric Strength of The 

strain a gas is capable of bearing without 
suffering disruption, or without permitting a 
disruptive discharge to nass through it. 

The dielectric strength of a gas depends — 

(i.) On the nature of the gas. 

(2.) On its pressure. 



<*as.] 



253 



[Gau. 



It has been calculated roughly that it requires 
.40,000 volts per centimetre to pass a disruptive 
discharge through dry air at ordinary pressures. 

Gas-Jet, Carcel Standard — (See 

Car eel Standard Gas- Jet.) 

Gas-Jet Photometer. — (See Photometer) 

Gas-Lighting, Electric The electric 

ignition of a gas-jet from a distance. 

Gas-Lighting, Multiple Electric 




Fig. 28 T. Multiple Gas- 
jet. 



A system of electric gas-lighting in which a 
number of gas-jets are lighted by means of 
a discharge of high electromotive force, 
derived from a Ruhmkorff coil or a static 
induction machine. 

Such devices are operated by means of minute 
electric sparks which are 
caused to pass through 
the escaping gas-jets. 

The spark for this pur- 
pose is obtained either by 
means of the extra current 
from a spark coil, by means 
of an induction coil or by 
static discharges. (See 
Currents, Extra. Coil, 
Spark. Coil, Induction.) 

A gas tip for use in multiple gas-lighting ap- 
paratus is shown in Fig. 281. The spark is 
formed immediately over the slot in the burner, 
and therefore ignites the escaping gas. 

Gas, Occlusion of The absorption 

or shutting up of a gas in the pores, or on the 
surfaces of various substances. 

Carbon possesses in a marked degree the prop- 
erty of occluding or absorbing gases in its pores. 
These occluded gases must be driven out from the 
carbon conductor employed in an incandescent 
lamp, since otherwise their expulsion, on the in- 
candesence of the carbon, consequent on the light- 
ing of the lamp, will destroy the high vacuum of 
the lamp chamber and thus lead to the ultimate 
destruction of the filament. (See Lamp, Electric, 
Incandescent.) 

Gassing. — The evolution of gas from the 
plates of a storage or secondary cell. 

Gastroscope. — An electric apparatus for 
the illumination and inspection of the human 
stomach. 



The light is obtained by means of a platinum 
spiral in a glass tube surrounded by a layer of 
water to prevent undue heating. The platinum 
spiral is placed at the extremities of a tube, pro- 
vided with prisms, and passed into the stomach 
of the patient. A separate tube for the supply 
of air for the extension of the stomach is also 
provided. 

Gastroscopy.— The examination of the 
stomach by the gastroscope. (See Gastro- 
scope.) 

Gauge, Battery.— A form of portable gal- 
vanometer, suitable for ordinary testing work. 
A form of battery gauge is shown in Fig. 282. 




Fig. 282. Battery Gauge. 

Gauge, Electrometer A device em- 
ployed in connection with some of Sir Wil- 
liam Thomson's electrometers to ascertain 
whether the needle, connected with the layer 
of acid that acts as the inner coating of the 
Leyden jar used in connection therewith, is at 
its normal potential. 

Gauge, Wire, American A name 

sometimes applied to the Brown & Sharpe 
Wire Gauge. (See Gauges, Wire, Varieties 
of) 

Gauge, Wire, Birmingham A term 

sometimes applied to one of the English wire 
gauges. 

Gauge, Wire, Gap A wire gauge in 

which gaps are left for the introduction of the 
wire to be measured. 



Gau.] 



254 



[Gau. 



Oauge, Wire, Micrometer 



-A gauge 



employed for accurately measuring the di- 
ameter of a wire in thousandths of an inch, 
based on the principle of the vernier or mi- 
crometer. (See Fig. 283.) 

The wire to be measured is placed between a 
fixed support B, and the end C, of a long mova- 
ble screw, which accurately fits a threaded tube a. 
A thimble D, provided with a milled head, fits 
over the screw C, and is attached to the upper 
part. The lower circumference of D, is divided 
into a scale of twenty equal parts. The tube A,is 
graduated into divisions equal to the pitch of the 
screw. Every fifth of these divisions is marked 
as a larger division. 

The principle of the operation of the gauge is 
as follows: Suppose the screw has fifty threads to 
the inch, the pitch of the screw, or the distance 
between two contiguous threads, is therefore ^ 
or .02 of an inch. 

One complete turn of the screw will, therefore, 
advance the sleeve D, over the scale a, the .02 of 
an inch. If the screw is only moved through 
one of the twenty parts marked on the end of 
the thimble or sleeve parts, or the ■£$ of a com- 



plete turn, the end C, advances towards B, the 

2V of &> *« *■> Ttnnr or - 001 inch - 

Suppose now a wire is placed between B and 
C, and the screw advanced until it fairly fills th& 




Fig. 283. Vernier Wire Gauge. 
space between them, and the reading shows two 
of the larger divisions on the scale a, three of the 
smaller ones and three on the end of the sleeve 
D, then 

Two large divisions of scale a = .2 inch 1 

Three smaller divisions of scale a.. = .06 " 
Three divisions on circular scale 

on D = .003 " 

Diameter of wire .263 

Serious inconvenience has arisen in practice- 



NEW LEGAL STANDARD WIRE GAUGE (ENGLISH). 

Tables of Sizes, Weights, Lengths and Breaking Strains of Iron Wire. 



Size on 


Diameter. 


Sectional 

area in 
sq. inches. 


Weight of 


Length of 


Breaking Strains. 


Size on 


Wire 
Gauge, 


Inch. 


Millimetres. 


100 yards. 


Mile. 

Lbs. 
3404 
2930 
2541 
2179 
1885 
1649 
1429 
1225 

i°37 
864 
732 
612 
502 
422 
348 
282 
223 
183 
148 
114 

88 

70 

56 

42 

32 

21 

18 


Cwt. 


Annealed. 


Bright. 

Lbs. 
15700 
13525 
11725 
10052 
8694 
7608 
6595 
5655 
4785 
399o 
338i 
2824 
2316 
1946 
1608 
1303 
1030 

845 

680 

532 

402 

326 

257 
197 
i45 
100 

82 


W ir e 
Gauge. 


7/° 

6/0 

5/° 

4/0 

3/0 

2/0 

J /o 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

*9 

20 


.500 
.464 
•432 
.400 
.372 
•348 
•324 
.300 
.276 
.252 
.232 
.212 
.192 
.176 
. 160 
.144 
.128 
.116 
.104 
.092 
.080 
.072 
.064 
.056 
.048 
.040 
.036 


12.7 
11. 8 
11. 
10.2 

9.4 
8.8 
8.2 
7.6 

i: 4 

5-9 
5-4 
4.9 
4-5 
4.1 

3-7 
3-3 

!:« 

2-3 
2. 

1.8 

1.6 
1.4 
1.2 

• 9 


.1963 
.1691 
.1466 
•1257 
.1087 
.0951 
.0824 
.0707 
.0598 
.0499 
.0423 

•0353 
.0290 
.0243 
.0201 
.0163 
.0129 
.0106 
.0085 
.0066 
.0050 
.0041 
.0032 
.0025 
.0018 
.0013 
.0010 


Lb 

193 
166 
144 
123 
107 
93 
81 
69 
58 
49 
4 [ 
34 
28 

24 
19 
16 
12 
10 
8 
6 
5 
4 
3 
2 

1 
1 


s. 
4 
5 

4 
8 

1 

7 
2 

9 
9 
t 
6 
8 


8 

7 
4 
4 
5 

2 

4 
8 
2 


Yards. 

58 

6 7 

78 

9 1 

105 

120 

138 

161 

190 

228 

269 

322 

393 

467 

566 

700 

882 

1077 

1333 

1723 

2240 

2800 

3500 

4667 

6222 

9333 

1 1 200 


Lbs. 

10470 

9017 

7814 

6702 

579 6 

5072 

4397 

377° 

3190 

2660 

2254 

1883 

1544 

1298 

1072 

869 

687 

564 

454 

355 

268 

218 

172 

131 

97 

67 

55 


7/0- 
6/0 
5/o 
4/o 
3/0 
2/0 
1/0 

2 
3 
4 
5 
& 

7 
8 

9 
10 
11 
12^ 
13 
14 
15 
16 

17 
18 

!9 

20 



(Issued by the Iron and Steel Wire Manufacturers' Association.) 



Gau.] 



255 



[Gau. 



from the numerous arbitrary numbers of sizes of 
wires employed by different manufacturers. 
These differences are gradually leading to the 
abandonment of arbitrary sizes for wires and em- 
ploying in place thereof the diameters directly in 
inches or thousandths of an inch. 

Gauge, Wire, Round — A device for 

accurately measuring the diameter of a wire. 

The round wire gauge shown in Fig. 284 is 
very generallv used for telegraph lines. Notches 




Fig. 284. Round Wire Gauge. 

for varying widths, cut in the edges of a circular 
plate of tempered steel, serve to approximately 
measure the diameter of a wire, the sides of the 
wire being passed through the slots. Numbers, 
indicating the different sizes of the wire, are 
affixed to each of the 
openings. 

Gauge, "Wire, Self- 
Registering A 

wire gauge arranged 
to give the exact di- 
ameter of the wire to 
be measured directly 
without calculation. 

A form of self- register- 
ing wire gauge is shown 
in Fig. 285. The wire 
or plate is inserted in the 
gap between a fixed and Fig 283. Wire and 
z. movable plate. The Plate Gauge. 

numbers corresponding to the diameter of the 
wire or plate are shown on one side of the gauge 
and the gauge numbers on the other side. 




Gauge, TVire, Standard A wire 

gauge adopted by the National Telephone 
Exchange Association at Providence, R. I., 
and by the National Electric Light As- 
sociation, at Baltimore, Md., in February, 
1886. 

The value of the standard as compared with 
the other gauges will be seen from an inspection 
of the table in this column: 

Gauges, Wire, Varieties of The 

following table gives a comparison of the 
principal wire gauges in use. 

COMPARISON OF THE DIFFERENT WIRE 
GAUGES. 



to 

3 

1- rt 


a** 

< 


i . 

I s 


Washburn & 
Moen Mfg. 

Co., Worces- 
ter, Mass. 


Trenton Iron 

Co., Trenton, 

N.J. 


6 

a 


£ s .a 

cm/ 


000000 






.46 








00000 






•43 


•45 






0000 


; 4 6*"" 


•454 


•393 


•4 


.400 




000 


.40964 


•425 


.362 


.36 


•37 2 




00 


.3648 


•38 


•33i 


•33 


•348 







•32495 


•34 


•307 


•305 


•324 




I 


.2893 


•3 


•283 


.285 


.300 




2 


•25763 


.284 


.263 


.265 


.276 




3 


.22942 


•259 


.244 


•245 


.252 




4 


•20431 


.238 


.225 


• 225 


•232 




5 


. 18194 


.22 


.207 


• 205 


.212 




6 


.16202 


.203 


.192 


.19 


.192 




7 


.14428 


.18 


.177 


•175 


.176 




8 


.12849 


.165 


.162 


.16 


: l60 




9 


■ XI 443 


.148 


.148 


•145 


.144 




10 


.10189 


•134 


• T 35 


•13 


.128 




n 


.090742 


. 12 


.12 


.1175 


.110 




12 


.080808 


•109 


.105 


.105 


. IO4 




13 


071061 


.095 


.092 


.0525 


.092 




14 


.064084 


.083 


.08 


■08 


.080 


.083 


15 


- 057068 


.072 


.072 


.07 


.072 


.072 


16 


.05082 


.065 


.063 


.061 


.O64 


.065 


17 


•04525- 


.c-,8 


.052 


.0525 


.O50 


.058 


18 


.040303 


.049 


.047 


•045 


.O48 


.049 


10 


•°3539° 


.042 


.O4I 


•039 


.O4O 


.o 4 


20 


.o 3 i 9 6r 


.035 


•035 


•034 


.O36 


•035 


21 


.0284^2 


.032 


.032 


•03 


.032 


•0315 


22 


•° 2 SM7 


.028 


.028 


.27 


.028 


•0295 


23 


•022571 


.025 


.C.25 


.024 


.024 


.027 


24 


.0201 


.022 


.023 


.0215 


.022 


•025 


25 


.0:79 


.02 


.02 


.019 


.020 


.023 


26 


•01594 


.018 


.0 8 


.018 


.Ol8 


.0205 


27 


.014195 


.016 


.017 


.017 


.Ol64 


.01875 


28 


.012641 


.014 


.016 


.016 


.OI48 


.0165 


29 


.011257 


.013 


.0.5 


•015 


•OI36 


•0155 


3° 


.010025 


.0: 2 


.014 


.014 


.OI24 


•C1375 


31 


.008Q28 


.01 


.0135 


.013 


.OIl6 


.01225 


32 


.00795 


.009 


.013 


.012 


.OI08 


.01125 


33 


.00708 


.008 


.011 


.011 


.OIOO 


.01025 


34 


.006304 


.007 


.01 


.01 


.0092 


.0095 


35 


.005614 


.005 


.0095 


.009 


.0084 


.009 


36 


.005 


.004 


.009 


.co8 


.OO76 


.0075 


37 


•004453 




.0085 


.00725 


.OO68 


.0065 


38 


.003965 




.008 


.0065 


.006 


•00575 


39 


•003531 




•oc 7 5 


•00575 


.OO5-' 


.005 


40 


003144 




.007 


.005 


.OO4S 


•0045 



(*au.J 



256 



[Gail. 



NUMBER, DIAMETER, WEIGHT, LENGTH AND RESISTANCE OF PURE COPPER 

WIRE. 

American Gauge. 







Weight, sp. gr. =8.889. 


Length. 


Resistance of Pure Copper at 70 


Fahrenheit. 


No. 


Diameter. 

Inches. 














Grs. per it. 


Lbs. per 1,000 
feet. 


Ft. per lb. 


Ohms per 1,000 ft. 


Feet per ohm. 


Ohms per lb. 


oooo. . . 


. 46000 


4475-33 


640.40 


1.56 


.051 


19605.69 


.0000798 


ooo... 


.40964 


3549-07 


507.01 


1.97 


.064 


15547-87 


.000127 


oo. . . 


.36480 


2814.62 


402.09 


2.49 


.081 


12330.36 


. 000202 


o. . . 


.32486 


2^33.28 


319.04 


3-i3 


.102 


9783.63 


.000320 


I.. . 


.28930 


1770.13 


252.88 


3-95 


.129 


7754.66 


.00051 


2. . . 


•25763. 


1403.79 


200.54 


4-99 


.163 


6149.78 


.000811 


3--- 


.22942 


1 1 13. 20 


I59-03 


6.29 


.205 


4876.73 


.001289 


4... 


.20431 


882.85 


126.12 


7 93 


•259 


3867.62 


.00205 


5. •• 


.18194 


700.10 


100.01 


10.00 


.326 


3067.06 


.00326 


6... 


. 16202 


555- 


79-32 


12.61 


.411 


2432.22 


.00518 


7... 


• '4429 


440.27 


62.90 


15.90 


•§i9 


1928.75 


.00824 


8... 


.12849 


349.18 


49/88 


20.05 


•654 


1529.69 


.01311 


9... 


•"443 


276.94 


39-56 


25.28 


.824 


1213.22 


.02083 


10... 


.10190 


219-57 


31-37 


31.88 


1.040 


961.91 


•03314 


11. .. 


.09074 


174-15 


24.88 


40.20 


1.311 


762.93 


.05269 


12. . . 


.08081 


138. 11 


19-73 


50.69 


1-653 


605.03 


.08377 


13-. 


.07196 


109.52 


15-65 


63.91 


2.084 


479.80 


•13321 


14... 


.06408 


86.86 


12.41 


80.59 


2.628 


380.51 


.2118 


15. • 


•05707 


68.88 


9.84 


101.63 


3-3I4 


301.75 


.3368 


16... 


.05082 


54-63 


7.81 


128.14 


4.179 


239-32 


•5355 


17... 


• 452 5 


43-32 


6., 9 


16159 


5.269 


189.78 


.8515 


18 .. 


.04030 


34-35 


4.91 


203.76 


6.645 


150.50 


1-3539 


19... 


•03589 


26.49 


3-78 


264.26 


8.617 


116.05 


2.2772 


20. . . 


.03196 


21.61 


3-09 


324.00 


10.566 


94.65 


3-423 


21. . . 


.02846 


17.13 


2.45 


408.56 


I3-323 


75.06 


5,443 


22. .. 


•025347 


13-59 


1.94 


sis^s 


16.799 


59-53 


8.654 


23... 


.022572 


10.77 


i-54 


649.66 


21.185 


47.20 


I3-763 


24... 


.0201 


8-54 


1.22 


819.21 


26.713 


37-43 


21.885 


25... 


.0179 


6.78 


•97 


1032.96 


33 684 


29.69 


34-795 


26... 


•OI594 


5-37 


•77 


1302.61 


42.477 


23-54 


55-331 


27... 


.014195 


4.26 


.61 


1642.55 


53-563 


18.68 


87.979 


28... 


.012641 


3.38 


.48 


2071 .22 


67.542 


14.81 


I39-893 


29... 


.011258 


2.68 


.38 


2611.82 


85.170 


11.74 


222.449 


30- • • 


.010025 


2.13 


•30 


3293-97 


107.391 


9-3 1 


353-742 


31- •• 


.008928 


!.6 9 


.24 


4152.22 


135.402 


7-39 


562.221 


32... 


.00795 


i-34 


.19 


5236.66 


170.765 


5-86 


894.242 


33--- 


.00703 


1.06 


• J 5 


660.271 


215.312 


4.64 


1421.646 


34- •• 


.0063 


.84 


.12 


8328.30 


271-583 


3.68 


2261.82 


35--- 


.00561 


.67 


.10 


10501.35 


342-413 


2.92 


3596.104 


36... 


.005 


•53 


.08 


13258.83 


431.712 


2.32 


57I5-36 


37- •• 


.00445 


.42 


.06 


16691.06 


544.287 


1.84 


9084.71 


38... 


.003965 


•34 


•05 


20854.65 


686.511 


1.46 


14320.26 


39- •• 


•003531 


.27 


.04 


26302.23 


865.046 


1. 16 


22752.6 


40... 


.003144 


.21 


•03 


33I75-94 


1091.865 


.92 


36223.59 



Gauss.- 

field. 



-The unit of intensity of magnetic 



The term gauss for unit of intensity of mag- 
netic field was proposed by S. P. Thompson as 
being that of a field whose intensity is equal to 
io 9 C. G. S. units, that is, io 8 lines of force per 
square centimetre. 

J. A. Fleming proposes, for the value of the 
gauss, such strength of field as would develop an 
electromotive force of one volt in a wire one 
million centimetres in length, moving through 
such a field with unit velocity. 

Fleming's value for the gauss was assumed on 
account of the small value of the gauss proposed 



by S. P. Thompson. It is one hundred times 
greater in value than Thompson's gauss. 

Sir William Thomson proposes, for the value of 
the gauss, such an intensity of magnetic field as is 
produced by a current of one weber (ampere) at 
the distance of one centimetre. 

Gauss, Fleming's Such a strength 

of magnetic field as is able to develop an 
electromotive force of one volt in a wire one 
million centimetres in length moved through 
the field with unit velocity. (See Gauss.) 

Gauss, S. P. Thompson's Such a 

strength of magnetic field that its intensity 
is equal to io 8 C. G. S. units. (See Gauss.) 



Gau.] 



257 



[Gen. 



Gauss, Sir William Thomson's 

Such an intensity of magnetic field as would be 
produced by a current of one ampere at the 
distance of one centimetre. (See Gauss.) 

Geissler Mercurial Pump.— (See Pump, 

Air, Geissler, Mercurial) 
Geissler Tubes.— (See Tubes, Geissler) 

General Faradization.— (See Faradiza- 
tion, General) 

General Galvanization.— (See Galvaniza- 
tion, General) 

Generation of Current by Dynamo-Elec- 
tric Machine.— (See Current, Generation of, 
by Dyna?no-Electric Machine) 

Generator, Dynamo-Electric An 

apparatus in which electricity is produced by 
the mechanical movement of conductors 
through a magnetic field so as to cut the 
lines of force. 

A dynamo-electric machine. (See Machine, 
Dynamo-Electric) 

A dynamo electric machine operates on the 
general principles of electro-dynamic induction. 
Strictly speaking, however, in a dynamo-electric 
generator the conductors are actually moved 
through the lines of force. In this respect, there 
fore, a dynamo-electric generator differs from a 
transformer, in which the lines of force are moved 
through the conductor. (See Induction, Electro- 
Dynamic. Transformer. Inauction, Mutual.) 

Generator, Motor A dynamo-elec- 
tric generator in which the power required to 
drive the dynamo is obtained from an elec- 
tric current. 

Motor generators are used in systems of elec- 
trical distribution for the purpose of changing 
the potential of the current. They consist of 
dynamos, the armatures of which are furnished 
with two separate windings, of fine and coarse 
wire respectively. One of these, generally the 
fine wire, receives the driving or motor cur- 
rent, usually of high potential, and the other, 
the coarse wire, furnishes the current used, usu- 
ally of low potential. 

The advantage of having the windings, which 
receive the driving current, of fine wire, is to 
enable a current of high potential to be dis- 
tributed ever the line from distant stations to 



places where it is desired to use the energy of the 
current at a much lower potential. 

Motor generators often consist simply of two 
distinct machines mechanically connected, one 
acting as a motor and the other as a dynamo. 

Motor generators are sometimes called dynamo- 
motors or dynamotors. 

Aldr.ch draws the following distinction between 
a dynamo-motor and a dynamotor : 

(i.) A dynamo motor is an energy transformer 
with the dynamo and motor in the same electric 
circuit. 

(2. ) A dynamotor is an energy transformer with 
the dynamo and motor in the same magnetic cir- 
cuit. 




Fig. 2Sb. Edison's Pyrj-Ma netic Generator. 

Generator, Pyro-Mag-netic An ap- 
paratus for producing electricity directly from 
heat derived from the burning of fuel. 



Gen.] 



258 



[Gil. 



The operation of the pyro-magnetic generator 
is dependent upon the fact that any variation in 
the number of lines of magnetic force that pass 
through a conductor will develop differences of 
electric potential therein. Such variations may 
be effected either by varying the position of the 
conductor as regards the magnetic field, or by 
varying the magnetic field itself. The latter 
method of generating differences of potential is 
utilized in the pyro-magnetic generator, and is 
effected in it by varying the magnetization of rolls 
of thin iron or nickel by the action of heat. 

A form of pyro-magnetic generator devised by 
Edison is shown in Figs. 286 and 287. 




Fig. 287. Edison's Pyro- Magnetic Generator, 

This apparatus is sometimes called a pyro- 
magnetic dynamo. 

Eight electro-magnets are provided, each with 
an armature consisting of a roll of corrugated 
iron. Each of these armatures is provided with 
a coil of insulated wire wound on it and pro- 
tected by asbestos pape:\ The armatures pass 
through two iron discs as shown. The armature 
coils are connected in series in a closed-circuit, 
the wires from the coils being connected with 
metallic brushes that rest on a commutator sup- 
ported on a vertical axis. A pair of metallic 
rings is provided above the commutator to carry 
off the current generated. 

The vertical axis is provided below with a semi- 
circular screen called a guard plate which rotates 
with the axis and cuts off or screens one-half the 
iron armatures from the heated air. 

When the axis is rotated, the difference in the 



magnetization of the armatures, when hot and 
cold, develops electromotive forces which result 
in the production of an electric current. 

Generator, Secondary A term fre- 
quently employed for a converter or trans- 
former. 

The word transformer is now almost univer- 
sally employed. (See Transformer.) 

Generator, Watt A term sometimes 

employed for stating the power in watts that 
any electric source is capable of producing. 

Estimating the power of a dynamo-electric 
machine by the number of watts it is capable of 
producing is very convenient in practice, and is 
now very generally adopted. A dynamo capable 
of furnishing a difference of potential of 1,000 
volts, and a current of 10 amperes, would be said 
to be a 10,000 watt-generator. 

The term watt-generator, though applicable to 
the case of any electric source, is in practice 
generally limited to the case of dynamo-electric 
machines or secondary batteries. 

Generators, Motor, Distribution of Elec- 
tricity by (See Electricity, Distribu- 
tion of, by Motor Generators^) 

Geographical Distribution of Thunder 
Storms. — (See Storms, Thunder, Geograph- 
ical Distribution of.) 

Geographical Equator. — (See Equator, 
Geographical^) 

Geographical Meridian. — (See Meridian, 
Geograph ica I.) 

German Silver Alloy. — (See Alloy, Ger- 
man Silver?) 

Gilding, Electric The electrolytic 

deposition of gold on any object. 

Electro-plating with gold. (See Plating, 
Electro?) 

The surfaces of the object to be gilded are 
made electrically conducting, if not already so, 
and are then connected to the negative terminal 
of a voltaic cell or other source, and immersed in 
a plating bath containing a solution of a salt of 
gold, directly opposite a plate of gold, connected 
with the positive terminal of the source. The 
objects to be plated thus become the kathode, and 
the plate of gold the anode of the plating bath. 
On the passage of a suitable current, the gold is 
dissolved from the plate at the anode and deposited 



Oil.] 



259 



[Gov, 



on the object at the kathode. (See Bath, Gold. 
Kathode. Anode. ) 

Gilt Plumbago. — (See Plumbago, Gilt) 

Gimbals. — Concentric rings of brass, sus- 
pended on pivots in a compass box, and on 
which the compass card is supported so as to 
enable it to remain horizontal notwithstand- 
ing the movements of the ship. (See Com- 
pass, Azi?nuth) 

Each ring is suspended on two pivots placed 
directly opposite each other, that is, at the ends 
of a diameter, which in one ring is at right angles 
to that in the other. 

Girder Armature. — (See Armature, Gir- 
der?) 

Globe, Vapor, of Incandescent Lamp 
A glass globe surrounding the cham- 
ber of an incandescent electric lamp, for the 
purpose of enabling the lamp to be safely 
used in an explosive atmosphere, or to permit 
the lamp to be exposed in places where water 
is liable to fall on it. 

Such a vapor globe is shown in Fig. 288. In 
the event of accidental breakage of the outside 
globe, the lamp chamber 
proper prevents the igni- 
tion of the explosive 
gases. In such cases, 
however, the outer pro- 
tecting chamber should 
be promptly replaced - 

In some forms of vapor 
globes, a valve is pro- 
vided, opening outwards, 
in order to permit the ex- 
panded air to escape 
when a given pressure is 
reached, and yet, at the 
same time, to prevent the 
entrance of gas or vapor 
from without. 

Glow Discharge. — 
(See Discharge, Glow.) 

Glow Lamp.— (See Lamp .Electric Glow.) 

Gold Bath.— (See Bath, Gold.) 

Gold-Leaf Electroscope. — (See Electro- 
scope, Gold-Leaf) 

Gold-Plating. — (See Plating, Gold) 

Gong, Electro-Mechanical A gong 




Fig. 288 



Globe. 



struck or operated by mechanical force at 
times which are dependent on the passage of 
an electric current. 

The motive power is the mechanical force de- 
veloped by a bent spring, the fall of a weight, 
etc., and, by suitable mechanism, is permitted to 
act only on the passage of an electric current. 

Governor, Centrifugal A device for 

maintaining constant the speed of a steam 
engine or other prime mover, despite sudden 
changes in the load or work. 

In a ball governor, any increase in speed 
causes the balls to fly out from the centre of rota- 
tion by centrifugal force. This motion is utilized 
to control a valve or other regulating device. If 
the speed of the engine falls, the balls move 
towards the centre, shifting the valve or regulat- 
ing device in the opposite direction. 

Governor, Current A current regu- 
lator. 

A device for maintaining constant the cur- 
rent strength in any circuit. 

Current governors are either automatic or non- 
automatic. (See Regulation, Automatic.) 

Governor, Electric A device for 

electrically controlling the speed of a steam 
engine, the direction of current in a plating 
bath, the speed of an electric motor, the re- 
sistance of an electric circuit, the flow of 
water or gas into or from a containing vessel, 
or for other similar purposes. 

The particular form assumed by the apparatus 
varies with the character of the work it is intended 
to accomplish. In some cases an ordinary ball 
or centrifugal governor is employed to open or 
close a circuit; or, a mass of mercury in a rotat- 
ing vessel is. caused, at a certain speed, to open or 
close a circuit; or, the resistance of a bundle of 
carbon discs is caused 10 vary, either by pressure 
produced by centrifugal force, or by the move- 
ment of an armature. 

Governor, Periodic A name ap- 
plied by Ayrton & Perry to a form of gover- 
nor for an electric motor, in which the cur- 
rent is automatically cut out for a certain 
portion of each revolution. 

Governor, Spasmodic — A name 

given by Ayrton & Perry to a form of gover- 
nor for an electric motor, in which the cur- 



Gov.] 



260 



[Gra- 



rent is automatically cut off in proportion as 
the work is cut off. 

The spasmodic governor consists essentially of a 
cone dipping into the surface of mercury in a rotat- 
ing vessel. As the speed of the governor increases 
on a lightening of the load, the surface of the mer- 
cury is curved by the increased centrifugal force, 
until finally the mercury leaves the contact point 
and thus cuts off the current. 

Governor, Steam, Electric A de- 
vice used in connection with a valve to so 
electrically regulate the supply of steam to an 
engine, that the engine shall be driven at 
such a speed as will maintain either a con- 
stant current or a constant potential. 

In the electric governor, the steam valve is 
operated by an electro-magnet, whose coils, in 
the case of a constant current machine, are of 
thick wire placed in the main circuit, and, in 
that of a constant potential machine, are of thin 
wire placed in a shunt around the mains. 

Graduators. — Devices, generally electro- 
magnetic, employed in systems of simultane- 
ous telegraphic and telephonic transmission 
over the same wire, so inserted in the line cir- 
cuit as to obtain the makes and breaks re- 
quired in a system of telegraphic communi- 
cation so gradually that they fail to sensibly 
influence the diaphragm of a telephone placed 
in the same circuit. 

Gramme. — A unit of weight equal to 
I 543 2 35 grains. 

The gramme is equal to the weight of one cubic 
centimetre of pure water at the temperature of its 
maximum density. It has various multiples and 
decimal divisions— of the former, the kilogramme 
or one thousand grammes is the most frequently 
used; of the latter, the centigramme or the one- 
hundredth of a gramme, and the milligramme or 
the one-thousandth of a gramme. (See Weights 
and Measures, Metric System of. ) 

Gramme Atom. — (See Atom, Gramme?) 

Gramme Molecule. — (See Molecule, 
Gramme?) 

Gramophone. — An apparatus for record- 
ing and reproducing articulate speech. (See 
Phonograph?) 

Gramophone Record. — (See Record, 
Gramophone?) 



Graphite.— A soft variety of carbon suit- 
able for writing on paper or similar surfaces. 

Graphite is the material that is employed for 
the so-called black lead of lead pencils. It is- 
sometimes called plumbago. Strictly speaking, 
the term graphite is only applicable to the variety 
of plumbago suitable for use in lead pencils. 

Graphite is used for rendering surfaces to be 
electro-plated, electrically conducting, and also for 
the brushes of dynamos and motors. For the 
latter purpose it possesses the additional advantage 
of decreasing the friction by means of its marked- 
lubricating properties. 

Graphophone, Micro A modifica- 
tion of the phonograph in which, instead of a 
single diaphragm, a number of separate non- 
metallic diaphragms are caused to act on a 
single diaphragm to record the speech, so that 
the separate diaphragms can be thrown into 
strong vibration when reproducing the speech. 

Graphophone, Phonograph A term 

sometimes applied to the graphophone. (See 
Graphophone, Micro. Phonograph?) 

Graphophone Record. — (See Record, 
Graphophone?) 

Gray's Harmonic Telegraphic Analyzer. 
— (See Analyzer, Grays Harmonic Tele- 
graphic?) 

' Gray's Harmonic Telegraphy. — (See Te- 
legraphy, Grays Harmonic Multiple?) 

Gravitation. — A name applied to the force 
which causes masses of matter to tend to 
move towards one another. 

This motion is assumed to be that of attraction, 
that is, the bodies are assumed to be drawn to- 
gether. It is not impossible, however, that they 
may be pushed together. 

Gravitation, like electricity, is well known, so 
far as its effects are concerned; but, as tj the true 
cause of either, particularly the former, we are in 
comparative ignorance. 

The general facts of gravitation may be suc- 
cinctly stated by the following law, generally 
known as Newton's law. 

Every particle of matter in the universe is at- 
tracted by every other particle of matter, and 
itself attracts every other particle of matter, with 
a force which is directly proportional to the pro- 
duct of the masses of the two quantities of matter 



Gra.] 



261 



[Gua. 



and inversely proportional to the square of the 
distance between them. 

Gravity Ammeter. — (See Ammeter, Grav- 
ity.) 

Gravity, Centre of The centre of 

weight of a body. 

Bodies supported at their centres of gravity are 
in equilibrium, since their weight is then evenly 
distributed around the point of support. 

Gravity-Drop Annunciator. — (See An- 
nunciator, Gravity-Drop) 

Gravity, Voltaic Cell (See Cell, 

Voltaic, Gravity) 

Gravity Voltmeter.— (See Voltmeter, 
Gravity.) 

Great Calorie. — (See Calorie, Great) 

Grenet Voltaic Cell.— (See Cell, Voltaic, 
Grenet) 

Grid. — A lead plate, provided with perfor- 
ations, or other irregularities of surface, and 
employed in storage cells for the support of 
the active material. 

The support provided for the active material 
on the plate of a secondary or storage cell. 

The grid receives its name from its resemblance 
to a gridiron. The active material is generally 
maintained on the grid by means of variously 
shaped apertures or holes. These are generally 
larger near the centre, so as to prevent the falling 
out of the material after it has been hardened by 
compression. (See Cell, Secondary. Cell, Stor- 
age.) 

Various forms have been given to the grid. 
The object of these forms, in general, is to in- 
sure the retention of the active material by the 
grid. 

The grids are preferably suspended from suit- 
able supports fastened to the top of the battery 
jars, instead of resting on the bottom of the bat- 
tery jars. 

Grip, Cable A grip provided for 

seizing the end of a cable when it is to be 
drawn into a duct or conduit. 

Grove's Voltaic Cell.— (See Cell, Voltaic, 
Grove) 

Grothuss' Hypothesis. — (See Hypothesis, 
Grothuss '.) 



Ground Circuit— (See Circuit, Ground) 

Ground Detector.— ( See Detector, 
Ground) 

Ground or Earth.— A general term for 
the earth when employed as a conductor, or 
as a large reservoir of electricity. 

The term ground is also applied to a fault 
caused by an accidental and undesired connection 
between an electric circuit, line or apparatus and 
the ground. (See Fault.) 

Ground Plate of Lightning Protec- 
tor. — (See Plate, Ground, of Lightning 
Protector) 

Ground-Eeturn. — A general term used 
to indicate the use of the ground or earth 
for a part of an electric circuit. 

The earth or ground which forms part of 
the return path of an electric circuit. 

The ground-return is generally used in the 
Morse system of telegraphy as practiced in the 
United States. 

Ground-Wire. — The wire or conductor 
leading to or connecting with the ground or 
earth in a grounded circuit. 

This is sometimes called an earth-grounded 
wire. 

A circuit is grounded when it is completed in 
part by the ground or earth. ' 

Grounded Circuit.— (See Circuit, 
Grounded.) 

Growth or Expansion of Lines of Force. 

— (See Force, Lines of, Growth or Expan- 
sion of) 



-A wire netting placed 



Guard, Fan — 

around the fan of an electric motor for the 
purpose of preventing its revolving arms 
from striking external objects. 

Guard, Lightning A term some- 
times used for lightning rod. (See Rod, 
Lightning) 

Guard, Transformer, Lightning 

A transformer lightning arrester. (See Ar- 
rester, Lightning, Transformer) 



Gua.] 



262 



[Hal. 



Guard, Wire Shade A guard of 

wire netting provided for the protection of a 
shade. 

A form of wire shade is shown in Fig. 289. 




Wire Shade Guard. 



Fig. 28 Q. 

Gutta-Percha. — A resinous gum obtained 
from a tropical tree, and valuable electrically 
for its high insulating powers. 

Gutta-percha readily softens by heat, but on 



cooling becomes hard and tough. Unlike India- 
rubber, it possesses but little elasticity. Its 
specific inductive capacity is 4.2, that of air being 
1, and of vulcanized rubber, 2.94. (See Capacity, 
Specific Inductive.) 

Gutta-percha is obtained largely from the East 
Indies, from a tree which yields a brownish gum. 
It is a fibrous and tenacious substance with but 
little flexibility, and is unaffected by acids. Oils 
produce less effect upon it than on India-rubber. 

Gutta-percha is one of the best insulating mate- 
rials known for sub-aqueous cables. 

Gymnotus Electricus.— The electric eel. 
(See Eel, Electric?) 

Gyrometer. — A speed indicator. (See In- 
dicator, Speed.) 



H. — A contraction for the horizontal inten- 
sity of the earth's magnetism. 

H. — A contraction proposed for one unit 
of self-induction. 

H. — A contraction used in mathematical 
writings for the magnetizing force that exists 
at any point, or, generally, for the intensity of 
the magnetic force. 

The letter H, when used in mathematical 
writings or formulae for the intensity of the 
magnetic force, is always represented in bold or 
heavy faced type, thus : H , 

H- Armature Core. — (See Core, Arma- 
ture, H.) 

Hail, Assumed Electric Origin of 

A hypothesis, now generally rejected, framed 
to explain the origin of the alternate coatings 
of ice and snow in a hail stone, by the alter- 
nate electric attractions and repulsions of 
the stones between neighboring, oppositely 
charged, snow and rain clouds. 

It is now generally recognized that the electric 
m mifestations attending hail storms are the 
effects and not the causes of the hail. (See Para- 
greles.) 

Hair, Electrolytic Removal of 

The permanent removal of hair from any part 



of the body, by the electrolytic destruction of 
the hair follicles. 

A platinum negative electrode is inserted in the 
hair follicle and the positive electrode, covered with 
moist sponge or cotton, is held in the hand of the 
patient. A current of from two to four 771HU -am- 
peres from a battery of from eight to ten Le- 
clanche elements is then passed for from ten to 
thirty seconds. A few bubbles of gas appear, 
and the hairs are then removed from the follicles 
by a pair of forceps. (See Milli- Ampere. ) 

When the work is properly done there is no 
destruction of the skin and therefore no marks or 
scars. 

In the removal of hair from the face, it is pref- 
erable that the current should slowly reach its 
maximum strength. 

Half-Shades for Incandescent Lamps. 

— Shades for incandescent electric lamps, in 
which one-half of the lamp chamber proper 
is covered with a coating of silver, or other 
reflecting surface for reflecting the light, or is 
ground for the purpose of diffusing the light. 
The half-shade is applicable to cases where it 
is desired to throw out the light, not in all direc- 
tions, but on one side only of any plane. Some- 
times the dividing plane is taken parallel to the 
length of the incandescing filament and sometimes 
at right angles to it. When the lamp is placed 



Hal.J 



263 



[Hea. 



within a surrounding globe the reflecting surface 
may be placed on this globe instead of on the 
lamp chamber. 

Hall Effect.— (See Effect, Hall.) 

Halleyan Lines. — (See Lines, Halleyan.) 

Halpine-Savage Torpedo.— (See Torpedo, 
Halpi?ie- Savage.) 

Handhole of Conduit.— A box or opening 
communicating with an underground cable, 
provided for readily tapping the cable, and 
of sufficient size to permit of the introduction 
of the hand. 

Hand-Lighting Argand Electric Burner. 
— (See Burner, Argand Electric, Hand- 
Lighter^) 

Hand-Lighting Electric Burner.— (See 
Bur?ier, Hand-Lighting Electric.) 

Hand-Re gulation. — ( See Regulation, 
Hand.) 

Hand-Regulator. — (See Regulator, 
Hand.) 

Hanger-Board. — (See Board, Hanger?) 

Hanger, Cable A hanger or hook 

suitably secured to the cable and designed to 
sustain the weight 
of the cable by 
intermediately sup- 
porting it on iron or 
steel wires strung 
above the cable. 

A cable hanger or 
cable clip is shown in 
Fig. 290. The mode 
of supporting the cable 
C, by the hanger hook 
H, will be readily un- 
derstood from an in- 
spection of the figure. F *' 2go - Cable Hanger ' 

The weight per foot of an aerial cable is gener- 
ally so great that the poles or supports would re- 
quire to be very near together, unless the device 
of intermediate supports, by means of cable clips 
or hangers, were adopted. 

Hanger, Double-Curve Trolley A 

trolley hanger generally employed at the ends 
of single and double curves, and on inter- 
mediate points on double track curves, sup- 
ported by lateral strain in opposite directions. 




Hanger, Single-Curve Trolley A 

trolley hanger supported on a single track 
curve, except at the ends and on the inside 
curve of a double track line, by lateral strain 
in one direction. 

Hanger, Straight-Line Trolley A 

trolley hanger on a straight trolley line suit- 
ably supported by a span wire so. as to have 
a vertical strain only. 

Hanger, Trolley A device for sup- 
porting and properly insulating trolley wires. 

Hard-Drawn Copper Wire. — (See Wire, 
Copper, Hard-Drawn.) 

Harmonic Receiver. — (See Receiver, Har- 
monic.) 

Harmonic Telegraphy. — (See Telegraphy, 
Grays Harmonic Multiple) 

Head Bath, Electric (See Bath, 

Head, Electric) 

Head Breeze, Electro-Therapeutic — — — 
(See Breeze, Head, Electro- Therapeutic.) 

Head Light, Locomotive, Electric 



An electric light placed in the focus of a par- 
abolic reflector in front of a locomotive engine. 
The lamp is so placed that its voltaic arc is a 
little out of the focus of the reflector, so that, by 
giving a slight divergence to the reflected light, 
the illumination extends a short distance on either 
side of the tracks. 

Heat. — A form of energy. 

The phenomena of heat are due to a vibratory 
motion impressed on the molecules of matter by 
the action of some form of energy. 

Heat in a body is due to the vibrations or 
oscillations of its molecules. Heat is transmitted 
through space by means of a wave motion in the 
univer-al ether. This wave motion is the same 
as that causing light. 

A hot body loses its heat by producing a wave 
motion in the surrounding ether. This process 
is called radiation. (See Radiation.) 

The energy given off by a heated body cooling 
is called radiant energy. 

Radiant energy is transmitted by means of 
ether waves; it is of two k.nds, viz.: 

(1.) Obsai?-,: Heat, or heat which does not 
affect the eye, although it can impress a photo- 
graphic image on a sufficiently sensitive photo- 
graphic plate. 



Hea.J 



264 



[Hea. 



(2.) Luminous Heat, or heat which accompanies 
light. (See Energy, Radiant.) 

Heat is conducted, or transmitted through 
bodies, with different degrees of readiness. 

Some bodies are good conductors of heat, 
others are poor conductors. 

Heat is transmitted through liquids by means 
of currents occasioned by differences in density 
caused by differences of temperature. These 
currents are called convection currents. 

Heat is measured as to its relative degree of in- 
tensity by the thermometer. It is measured as to 
its amount or quantity by the calorimeter. (See 
Ther??iometer, Electric. Calorimeter.) 

The heat unit most commonly employed is, 
perhaps, the calorie, or the amount of heat re- 
quired to raise one gramme of water one degree 
centigrade. 

Another heat tinit, very generally employed in 
the United States and England, is the quantity of 
heat required to raise one pound of water one de- 
gree Fahrenheit. This is called the English heat 
unit. (See Calorie. Units, Heat. Joule. Volt- 
Coulomb.) 

Heat, Absorption and Generation of, in 

Voltaic Cell The heat effects which 

attend the action of a voltaic cell. 

The chemical action of the exciting liquid or 
electrolyte on the positive plate or element of a 
voltaic cell, like all cases of chemical combination, 
is attended by a development of heat. 

When, however, the circuit of the cell is closed, 
the energy liberated during the chemical combi- 
nation appears as electricity, which develops heat 
in all parts of the circuit. (See Heat, Electric. 
Cell, Voltaic. ) 

Heat, Atomic A constant product 

obtained by multiplying the specific heat of 
an elementary substance by its atomic weight. 
(See Weight, Atomic) 

Dulong and Petit have discovered the remark- 
able fact that the product of the specific heat of 
all elementary substances by their atomic weights 
is nearly the same. The product is called the 
atomic heat, and is about equal to 6.4. 

Dulong and Petit's law may be stated as fol- 
ows, viz. : All elementary atoms require the same 
quantity of heat to heat them to the same number 
of degrees. 

The atomic heat of any body divided by its 
specific heat gives its atomic weight. 



The heat imparted to any body performs three 
kinds of work, viz. : 

(1.) That expended in external work, such, 
for example, as in overcoming the atmospheric 
pressure. 

(2.) That expended in internal work, or in 
overcoming the attractions of the atoms and driv- 
ing them apart. 

(3.) That expended in overcoming the temper- 
ature, or the true specific heat, or heat expended 
in increasing the molecular vis-viva. 

The expenditure of energy is greatest in the 
third head. The exact value of the three factors 
is as yet unknown, and in the opinion of Weber 
and others the correctness of Dulong and Petit's 
law cannot be regarded as being satisfactorily 
established. 

Regnault has proved that Dulong and Petit's law 
is true for compound bodies, i. e., in all compounds 
of similar composition the product of the specific 
heat by the total chemical equivalent is constant. 

The following table from Anthony and Bracket 
illustrates the law of Dulong and Petit: 



Elements. 



Iron 
Copper. . 
Mercury 
Silver . . . 
Gold 

Tin 

Lead 

Zinc 



Specific Heat 


Atomic 


of Equal Weight. 


Weight. 


0.114 


55-9 


0.095 


63-17 


0.0314 (Solid) 


199.71 


0.057 


107.67 


0.0329 


196.15 


0.056 


117. 7 


0.0314 


206.47 


0.0955 


64.9 



Product of 
Specific 

Heat into 
Atomic 
Weight. 



6.372 
6.001 
6.128 
6 -i37 
6-453 
6.591 
6.483 
6.108 



"This product— the atomic heat of elements,, 
the molecular heat of compounds— has the follow- 
ing physical meaning: Of any substance whose 
atomic or molecular weight we know, we may 
take a number of grammes numerically equal to 
the atomic or molecular weight; for example, 
35-5 grammes of chlorine, 16 grammes of marsh 
gas; we may call such quantity the gramme atom 
or the gramme molecule of the substance. The 
atomic heat or the molecular heat of a substance 
is the number of calories of heat necessary to 
raise the temperature of a gramme atom or a 
gramme molecule of the substance through 1 
degree C." — {Daniel I.) 

Heat, Electric The heat developed 

by the passage of an electric current through 
a conductor. 



Hea.] 



2H5 



[Hea. 



Heat is developed by the passage of a current 
through any conductor, no matter what its resist- 
ance may be. 

If the conductor is of considerable length, and 
of good conducting power, the heat developed is 
not very sensible, since it is spread over a consid- 
erable area, and is rapidly lost by radiation. 

H, the heat generated in any conductor of a 
resistance R, by the passage through it of an elec- 
tric current C, is equal to 

H = C 3 R, in watts. 

But one watt = . 24 small calorie per second. 

Therefore, the heat which is generated, 
H = C 2 R X - 2 4 calories per second. 

For the case of a uniform wire of circular cross- 
section the resistance R, in ohms is directly pro- 
portional to the length 1, and inversely propor- 
tional to the area of cross-section 7Tr 3 , or 



—t; that is, H = C 2 



&)■ 



The temperature to which a wire of a given re- 
sistance is raised, will of course vary with the 
mass of the wire, its radiating surface, and its 
specific heat capacity. If the same number of 
heat calories are generated in a small weight of a 
conductor, whose radiating surface is small, the 
resulting temperature will of course be far higher 
than if generated in a larger mass provided with 
a much greater radiating surface. In general, 
however, its temperature increases as the square 
of the current strength when the resistance is con- 
stant, and increases as the resistance of the wire 
per unit of length is greater. 

The temperature a wire acquires by the passage 
of a current through it varies inversely as the 
third power of the radius. If two wires of the 
same material have the same lengths, but different 
radii, the temperature, acquired by the pas- 
sage of an electric current, will depend on the 
heat developed per second, le>s that radiated per 

second. Since the former varies as — , and the 

r J 

latter as r, that is, as 1 X 27rr, the temperatures 
attained vary as — , and not as -I, as frequently 

stated. — {Larden.) 

The current required to raise the temperature 
of a bare copper wire a given number of degrees 
above the temperature of the air is given in the 
following table : 



BARE COPPER WIRES. 

Current required to increase the temperature of a copper 
wire t° Centigrade above the surrounding air, the 
copper wire being bright polished or blackened. 



Diameter in 

Centimetres 

and Mils 


Current in Amperes. 


(thousandths of 
an inch). 


t = i°C. 


t = 9 °C. 


t = 25 C. 


Cm. 


Mils. 


Bright 


Black 


Bright 


Black 


Bright 


Black 


.2 
•3 
•4 

.6 

•7 

.8 

•9 
1.0 
2.0 

3-o 
4.0 
5-o 
6.0 
7.0 
8.0 
9.0 
10. 
34-4 


40 
80 
120 
160 
200 
240 
280 
310 
350 
390 
790 
1180 

1570 
1970 
2360 
2760 
3150 
3S4° 
3940 


1.0 

2.8 

5-2 

8.0 
II. I 

14 6 
18.5 

22.6 
26.9 

89.2 
164 

252 
353 
463 

584 
714 
851 
997 


1.4 

3-9 
7.2 
n. 

15.4 
20.3 

25.6 
3i-3 
37-3 
43-6 

123 

227 

349 

488 

642 

808 

988 
i« 7 8 
1380 


3.0 

8-3 
i5-3 
23.6 

33-° 
43-4 
54 6 
66.7 
79.6 

93-3 
204 

485 
746 

i°43 
i37i 
1728 
2110 

25>9 
2950 


4.1 
"•5 

21.2 
32.7 
45-7 
00.0 
7.5.6 

92.4 
no 

129 

365 
671 

'035 
1444 

1828 
2392 

2922 

3486 

4084 


4 .8 

13-5 

24.9 

38.3 
53-5 
70.3 
88. 7 

108 

129 

151 

428 

787 
1211 

l6 99 
2225 
2803 
3422 
4088 
4788 


6.6 
18.7 

34-4 

53-0 
74-i 
97.4 
123 

150 

179 

210 

593 
1090 
1675 
2343 
3080 
3882 
4741 
5659 
6626 




















— {Forbes.) 

Heat, Electric Convection of A 

term employed to express the dissymmetrical 
distribution of temperature that occurs when a 



Hea.] 



26$ 



[Hea. 



current of electricity is sent through a 
metallic wire, the middle of which is main- 
tained at a constant temperature, and the 
ends at the temperature of melting ice. 

The distribution of heat during the pas- 
sage of a current through an unequally- 
heated conductor. 

If the central portions of a metallic bar are 
heated the curve of heat distribution is sym- 
metrical. On sending an electric current through 
the wire it is heated according to Joule's law, 
and the curve of heat distribution is still sym- 
metrical. But the current in passing from the 
colder to the hotter parts of the wire produces 
an additional heating effect at this point, and in 
passing from the warmer to the colder parts of 
the wire produces a cooling effect. (See Effect, 
Peltier. Effect, Thomson.) The curve of heat 
distribution is then no longer symmetrical. The 
term Electrical Convection of Heat, has been 
given to the dissymmetrical distribution of heat 
so effected. 

Sir William Thomson, who studied these 
effects, found that the electrical convection of 
heat in copper takes place in the opposite 
direction to that in iron; that is to say, the elec- 
trical convection of heat is negative in iron, (i. e., 
the direction is opposite to that of the current), 
and positive in copper. 

Heat, Irreversible Heat pro- 
duced in a homogeneous conductor by the 
passage of electricity through it. 

This heat, according to Joule's law, is propor- 
tional to the square of the current, and is produced 
no matter in what direction the current is pass- 
ing. In this respect it is unlike the heat pro- 
duced by the passage of electricity through a 
heterogeneous conductor, in which case heat is 
developed or liberated only by the passage of the 
current in a given direction : on the passage of the 
current in the opposite direction, heat being 
absorbed and the temperature lowered. (See 
Heat, Reversible.) 

Heat Lightning". — (See Lightning, Heat.) 



Heat, Luminous 



-A variety of radi- 



ant energy which affects the eye, as light. 

Radiant heat and light are, in reality, different 
effects produced by one and the same cause, viz., 
by vibrations or waves in the universal ether. 
In general the waves producing heat are of 



greater length and smaller frequency than are 
those producing light. 

Heat, Mechanical Equivalent of 

The amount of mechanical energy, converted 
into heat, that would be required to raise the 
temperature of I pound of water i degree 
Fahr. 

The mechanical equivalence between the 
amount of energy expended and the amount 
of heat produced, as measured in heat units. 

Joule's experiments, the results of which are 
generally accepted, gave 772 foot-pounds as the 
energy equivalent to that expended in raising the 
temperature of I pound of water I degree Fahr. 

Heat, Molecular The number of 

calories of heat required to raise the tempera- 
ture of one gramme-molecule of any sub- 
stance 1 degree C. (See Molecule, Gramme* 
Heat, Atomic?) 

Heat, Obscure A variety of radiant 

energy which does not effect the eye. 

Radiant heat is sometimes divided into lumi- 
nous heat and obscure heat. (See Heat, Lumi- 
nous.) 

Heat, Red — The temperature at 

which a body, whose temperature is gradually 
increasing, begins to glow or to emit red rays 
of light. 

When a refractory solid body is gradually 
heated to incandescence, the red waves of light 
are first emitted, then the orange, and successively 
afterwards the yellow, green, blue, indigo and 
violet, when the body emits white light or is 
white hot. 

Heat, Reversible The heat pro- 
duced in a heterogeneous conductor by the 
passage through it of an electric current in a 
certain direction. 

Reversible heat is produced at the junction of 
two metals, where a difference of potential exists 
between them, or where their heterogeneity is 
greatest. It is called reversible because it de- 
pends upon the direction in which the :urrent 
is passing. If the current be passed in a certain 
direction across the junction, heat is liberated; 
while, if it be passed in the opposite direction, 
heat is absorbed, or cold results. 

Reversible heat effects are seen in the Peltier 
effect. (See Effect, Peltier.) 



Hea.] 



267 



[Hei. 



Heat, Specific The capacity of a 

substance for heat as compared with the 
capacity of an equal quantity of some other 
substance taken as unity. 

Water is generally taken as the standard for 
comparison, because its capacity for heat is greater 
than that of any other common substance. 

Different quantities of heat are required to 
raise the temperature of a given weight of dif- 
ferent substances through I degree. The spe- 
cific heats of substances are generally compared 
with water or with hydrogen, the capacity of 
these substances for heat being very great. 

According to Dulong and Pettit, the specific 
heat of all elementary atoms is the same. For 
example, the heat energy of an atom of hydrogen 
is equal to that of an atom of oxygen, but since 
a given mass of hydrogen, under similar condi- 
tions of temperature and pressure, contains sixteen 
times as many atoms as an equal mass of oxygen, 
therefore, when compared weight for weight, 
hydrogen has a specific heat sixteen times greater 
than that of oxygen. 

Or, in general, conparing equal weights, the 
specific heat of an elementary substance is in- 
versely proportional to its atomic weight. (See 
Heat, Atomic.) 



Heat, Specific, of Electricity 

Electricity, Specific Heat of.) 



—(See 



Heat Unit. — The quantity of heat required 
to raise a given weight of water through 
a single degree. 

There are a number of different heat units. 
The most important are: 

(i.) The British Heat Unit, or Thermal Unit, or 
the amount of heat required to raise I pound 
of water I degree Fahr. This unit represents an 
amount of work equal to 772 foot pounds. 

(2.) The Greater Calorie, or the amount of heat 
required to raise the temperature of 1,000 
grammes of water I degree C. (See Calorie.) 

(3.) The Smaller Calorie, or the amount of heat 
required to raise the temperature of one gramme 
of water I degree C. 

(4.) The Joule, orthe quantity of heat developed 
in one second by the passage of a current of one 
ampere through a resistance of one ohm. 

1 joule equals .0002407 large calories. 

I joule equals .2407 small calories. 

I foot-pound equals 1.356 joules. 



I pound-Centigrade equals 1884.66 joules. 

I *• •' '• 1389.6 foot pounds. 

I '* Fahrenheit -' 1047.03 joules. 

Heat Unit, English — (See Units, 

Heat.) 

Heat Unit or Calorie.— (See Calorie.) 

Heat Unit or Joule.— (See Joule) 

Heat, White The temperature at 

which light of all wave lengths from the red 
to the violet is emitted from a heated body, 
and the body, therefore, glows with a white 
light. 

A solid substance heated to white incandescence 
emits a continuous spectrum, i. e., a spectrum in 
which all the wave lengths of light from the red 
to the violet are present. 

Heater, Electric A device for the 

conversion of electricity into heat for purposes 
of artificial heating. 

Electric heaters consist essentially of coils or 
circuits of some refractory metal through which 
the current is passed. These coils or circuits are 
surrounded by air or finely divided solids, and are 
placed inside metallic boxes or radiators, which 
throw off or radiate the heat produced. 

When employed for the heating of liquids the 
coils are placed directly in the liquid to be 
heated, or are surrounded by radiating boxes 
placed in the liquid. 

Heating" Effects of Currents. — (See Cur- 
rents, Heating Effects of.) 

Hedgehog- Transformer. — (See Trans- 
former, Hedgehog.) 

Hecto-Ampere One hundred am- 
peres. 

Heliograph. — An instrument for tele- 
graphic communication that operates by em- 
ploying flashes of light to represent the dots 
and dashes of the Morse alphabet, or the 
movements of the needles of a needle tele- 
graph to the right or the left. (See Alphabet, 
Telegraphic) 

The flishes of light are thrown from the sur- 
face of a plane mirror. Motions to the right or 
left may be employed in order to distinguish 
between the dots and dashes, or the same may be 
effected by the relative durations of the flashes of 



Hel.] 



268 



[Hoi. 



light, or by the intervals between successive 
flashes. 

Telegraphic communication has been carried 
on between steamers during foggy weather by 
means of their fog horns; or between locomotives 
by their steam whistles. 

Helix, Dextrorsal — 



— A name some- 
times applied to a dextrorsal solenoid. (See 
Solenoid, Dextrorsal)) 

The magnetic polarity of a helix or solenoid 
depends not only on the direction in which the 
current is passed, but also on the direction in 
which the wire is coiled or wound. (See Magnet, 
Electro.) 

Helix, Sinistrorsal A name some- 
times applied to a sinistrorsal solenoid. (See 
Solenoid, Sinistrorsal)) 

Hemihedral Crystal.— (See Crystal, Hem- 
ihedral.) 

Henry, A The practical unit of self- 
induction. 

It has been generally agreed in the United 
States to call the practical unit of self-induction 
a henry, in place of a secohm or quadrant. 
The name henry should be adopted, not only by 
American electricians, but also by those of other 
countries, since the terms secohm or quadrant 
are contrary to the generally adopted usage of 
employing for such the names of distinguished 
electricians, who have passed from their labors. 

The fact that of all discoverers in the field of self- 
induction, none possesses so great a claim as that of 
Prof. Henry, must be generally acknowledged. 
As early as 1832 he published in Silliman's Jour- 
nal a paper in which he described experiments, 
showing clearly that the spark obtained by break- 
ing the current of a battery, in which along wire 
was interposed, was greater than when a short 
wire was employed, and that this increased length 
of spark was further increased by coiling the wire, 
and that the phenomena were ascribed to the ac- 
tion of the current on itself. 

A committee of the American Institute of 
Electrical Engineers, after careful consideration, 
recommended to the Institute that the value of 
the practical unit of inductance should be equal to 
109 C. G. S. units of inductance, usually ex- 
pressed by a length equal to one earth quadrant 
or 1 000,000,000 centimetres. 

The value of the practical unit of inductance, 
or the ' ' henry, " may in some cases be too high for 



convenience; in such cases it may be expressed 
by some fractional dimension, such, for example, 
as millihenry. 

Hercules Stone.— (See Stone, Hercules.) 
Hermetical Seal. — (See Seal, Hermeti- 
cal.) 

Hertz's Theory of Electricity. — (See Elec- 
tricity, Hertz 's Theory of.) 

Heterostatic. — A term applied by Sir 
William Thomson to distinguish a form of 
electrometer in which the electrification is 
measured by determining the mutual influ- 
ence of the attraction exerted by the charge 
to be measured and the attraction of an oppo- 
site charge imparted to the instrument by a 
source independent of the charge to be meas- 
ured. 

The term heterostatic distinguishes this form of 
electrometer from an idiostatic instrument, or one 
in which the measurement is effected by deter- 
mining the repulsion between the charge to be 
measured and the repulsion of a charge of the 
same name, i. <?., positive or negative, imparted 
to the instrument 'from an independent source. 
(See Electrometer.) 

Hick's Automatic Button Repeater.— 

(See Repeaters, Telegraphic)) 

Higii-Bars. — A term applied to those com- 
mutator segments, or parts of commutator 
segments, which, through less wear, faulty 
construction or looseness, are higher than ad- 
joining portions. (See Commutator.) 

High-Frequency Currents, Electric Light- 
ing by (See Lighting, Electric, by 

High-Freque7icy Currents?) 

High Resistance Magnet. — (See Magnet, 
High Resistance)) 

High Speed Electric Motor. — (See Mo- 
tor, Electric, High Speed)) 

High Tension Electric Fuse. — (See Fuse, 
Electric High Tension.) 

Hissing of Arc. — (See Arc, Hissing of.) 

Holder for Safety Fuse. — A box or other 
receptacle of refractory material for holding 
a safety fuse, and catching the molten metal 
when fused. 

The holder or fuse box is provided to prevent the 



Hoi.] 



269 



[Hor. 



molten metal of the fuse from setting fire to any 
combustible material on which, it might other- 
wise fall. 

Holders, Carbon, for Arc Lamps 

A clutch or clamp attached to the end of the 
lamp rod or other support, and provided to 
hold the carbon pencils used on arc lamps. 
(See Lamp, Arc, Electric?) 

Holders for Brushes of Dynamo-Electric 

Machine.— A device for holding the collect- 
ing brushes of a dynamo-electric machine. — 
(See Machine, Dynamo-Electric) 

Hole, Armature — A term sometimes 

applied for armature bore or chamber. (See 
Bore, Armature?) 

Hole, Armature Bore, Elliptical : 

An armature bore or chamber ellipsoidal in 
shape. 

Holohedral Crystal. — (See Crystal, Holo- 
Jiedral.) 

Holtz Machine. — (See Machine, Holtz.) 

Home Station. — (See Station, Home) 

Homogeneous Current Distribution. — 
(See Current, Homogeneous Distribution of.) 

Hood for Electric Lamp. — A hood pro- 
vided for the double purpose of protecting the 




Fig. 2QI. Arc Lamp Hood. 

body of an electric lamp from rain or sun, 
and for throwing its light in a general down- 
ward direction. 

Hoods for arc lamps are generally conical in 
shape. 



A form of hood for an exposed arc lamp is 
shown in Fig. 291. 

Horizontal Component of Earth's Mag- 
netism. — (See Component, Horizontal, of 
Earth's Magnetis?n.) 

Horns, Following", of Pole Pieces of 

a Dynamo - Electric Machine —The 

edges or terminals of the pole pieces of a dy- 
namo-electric machine towards which the 
armature is carried during its rotation. 




Fig 2Q2. Horns of Dynamo. 

According to S. P. Thompson, the following 
horns, b, d, Fig. 292, are those towards which 
the armature is carried ; the leading horns, a, c, 
those from which it is carried. 

As the change in the magnetic intensity is more 
sudden when the armature is moved from the 
pole pieces, and least when moved towards them, 
it is clear that the leading horns in a dynamo- 
electric machine, and the following horns in an 
electric motor, become heated during rotation by 
the production of Foucault currents. (See Cur- 
rents, Foucault. Machine, Dynamo Electric.) 

Horns, Leading, of Pole Pieces of a Dy- 
namo-Electric Machine The edges 

or terminals of the pole pieces of a dynamo- 
electrical machine from which the armature 
is carried during its rotation. 

Thus, in Fig. 292, a and c, are the leading horns 
of the pole pieces. 

Horns of Pole Pieces of Dynamo-Electric 
Machine.— The edges of the pole pieces of a 
dynamo-electric machine towards or from 
which the armature is carried during its rota- 
tion. 

These are called the following and the leading 
horns. 



Horse-Power. — A commercial 
power or rate of doing work. 



unit for 



Hor.] 



270 



[Hou. 



A rate of doing work equal to 33,000 pounds 
raised 1 foot per minute, or 550 pounds raised 
1 foot per second. 

A rate of doing work equal to 4,562.33 
kilogrammes raised 1 metre per minute. 

A careful distinction must be drawn between 
work and power. The same amount of work 
is done in raising I pound through 10 feet 
whether it be done in one minute or in one hour. 
The power expended or the rate of doing work 
is, however, quite different, being in the former 
case sixty times greater than in the latter. 
I horse-power = 550 foot-pounds per second. 

" = 33,000 foot-pounds per min- 

ute. 
" = 4,562.33 kilogramme-metres 

per minute. 
" = 745,941 watts. 

u = 1. 01385 metric horse-power. 

Horse-Power, Electric (See Power, 

Horse, Electric.) 

Horse-Power Hour. — (See Hour, Horse- 
Power). 

Horse-Power, Metric A unit of 

power in which rate of doing work is equal 
to 75 kilogramme-metres. (See Horse- 
Pcwer.) 

Horseshoe Electro-Magnet. — (See Mag- 
net, Electro, Horseshoed) 

Horseshoe Magnet. — (See Magnet, Horse- 
shoe.) 

Hot, Red — Sufficiently heated to 

emit red light only. (See Heat, Red.) 

Hot St. Elmo's Fire.— (See Eire, Hot, St. 
Elmo's.) 

Hot, White Sufficiently heated to 

emit all the colored lights of the spectrum. 
(See Heat, White.) 

Hotel Annunciator. — (See Annunciator, 
Hotels, 

Hour, Ampere ■ — A unit of electrical 

quantity equal to one ampere flowing for one 
hour. 

The ampere-hour is in reality a unit of quanti- 
ty like the coulomb. It is used in the service of 
electric currents, and is equal to the product of 
the current delivered by the time in hours. The 
ampere-hour is not a measure of energy, but when 



combined with the volt, and expressed in watt 
hours, it is a measure of energy. 

The capacity of any service for maintaining a 
flow of current is measured in ampere-hours. 
Thus, if any service, such as a primary or sec- 
ondary battery, has a capacity of 80 ampere- 
hours, it will supply 8 amperes for ten hours, or 
it may give 10 amperes for eight hours. 

The storing capacity of accumulators is gener- 
ally given in ampere-hours. The same is true of 
primary batteries. 

One coulomb equals .0002778 ampere-hours. 

One ampere-hour equals 3,600 coulombs. 

Hour, Horse-Power A unit of work. 

An amount of work equal to one horse- 
power for an hour. 

One horse power is equal to 1,980,000 foot- 
pounds, or 745.941 watt hours. 

Hour, Kilo-Watt A unit of electri- 
cal power equal to a kilo-watt maintained for 
one hour. 

Hour, Lamp Such a service of elec- 
tric current as will maintain one electric lamp 
during one hour. 

The number of lamp-hours is obtained by mul- 
tiplying the number of lamps by the average 
number of hours during which the lamps are 
burning. 

The use of lamp-hours is for the purpose of 
estimating the current supplied to a consumer by 
counting the number of hours each lamp is in 
service. 

To convert lamp-hours to watt-hours, multiply 
the number of lamp-hours by the number of 
watts per lamp. The watt hours, divided by 746, 
will then give the electrical horse-power hours, 
(See Hour, Watt.) 

Hour, Watt A unit of electrical- 
work. 

An expenditure of an electrical work of 
one watt for one hour. 

Lamp-hours are converted to watt-hours by 
multiplying the number of lamp-hours by the 
number of watts per lamp. (See Hour, Lamp.) 

House Annunciator. — (See Annunciator, 
House.) 

House Main. — (See Main, House.) 
House-Service Conductor.— (See Conduc- 
tor, House-Service.) 



Hou.] 



271 



[Hyp. 



House-Top Fixtures, Telegraphic 



(See Fixtures, Telegraphic House- Top.) 

House Wire. — (See Wire, Housed 

Hughes' Electro-Magnet.— (See Magnet, 
Electro, Hughes '.) 

Human Body, Electric Resistance of 

— (See Body, Human, Resistance of.) 

Hydro-Electric Bath. — (See Bath, Hydro- 
Electric^) 

Hydro-Electric Machine, Armstrong's 
(See Machine, Armstrong s Hydro- 
Electric^) 

Hydrogen, Electrolytic Hydrogen 

produced by electrolytic decomposition. 

It is the electrolytic hydrogen liberated in a 
voltaic cell at the surface of the negative plate, 
which causes polarization and consequent de- 
crease in the resulting current strength, by rea- 
son both of the counter-electromotive force it 
produces and the increased resistance it produces 
in the cell. 

Electrolytic hydrogen is atomic hydrogen; i. e., 
hydrogen with its bonds open or free. It there- 
fore possesses much stronger chemical affinities 
than does molecular hydrogen. Electrolytic 
oxygen which is evolved at the same time as the 
electrolytic hydrogen has been successfully em- 
ployed in electric bleaching. Hydrogen per- 
oxide is also formed and acts as a bleaching agent. 

Hydrometer or Areometer. — An appa- 
ratus for determining the specific gravity of 
liquids. (See Areometer or Hydrometer^) 

Hydro-Plastics. — (See Plastics, Hydro.) 

Hydro-Plasty. — The art of hydro-plastics. 
(See Plastics, Hydro.) 

Hydrotasimeter, Electric An elec- 
trically operated apparatus designed to show 
at a distance the exact position of any water 
level. 

In most forms of the electric hydrotasimeter a 
float placed in the liquid and connected with an 
electric circuit breaks this circuit, and, at intervals, 
sends positive impulses into the line when rising 
and negative impulses when falling. These are 
registered by means of an index moved by a step- 
by-step motion, positive currents moving it in 
one direction and negative currents moving it in 
the opposite direction. 



Hygrometer. — An apparatus for determin- 
ing the amount of moisture in the air. 

Hygrometrical. — Of or pertaining to the 
hygrometer. 

Hygrometrically. — In the manner of the 
hygrometer. 

Hypothesis. — A provisional assumption of 
facts or causes the real nature of which is 
unknown, made for the purpose of studying 
the effects of such causes. 

When the facts assumed by a hypothesis can 
be shown to be presumably true the hypothesis 
becomes a theory. A theory, therefore, gives a 
more correct expression of the relations between 
the causes and effects of natural phenomena than 
does a hypothesis. 

Hypothesis, Double-Fluid Electric 

— (See Electricity, Double-Fluid Hypothesis 
of.) 

Hypothesis, Grothuss' A hypothe- 
sis proposed by Grothuss to account for the 
electrolytic phenomena that occur on closing 
the circuit of a voltaic cell. 

Grothuss' hypothesis assumes: 

(i.) That before the electric circuit is closed 
the molecules of the electrolyte are arranged in 
an irregular or unpolarized condition, as repre- 




Fig. 2Q3» Grothuss' Hypothesis of Electrolytic Polari- 
zation. 

sented at (i), Fig. 293. These molecules are 
shaded as shown in Fig. 294, to indicate their com- 
position and polarity. 

(2.) When the circuit is closed and a current 



Hyp.] 



272 



[Hys. 



begins to pass, a polarization of the electrolyte, as 
shown at (2), ensues, whereby all the negative 
ends of the molecules of hydrogen sulphate, o 
sulphuric acid, are turned towards the positive 
or zinc plate, and all the positive ends towards 
the negative or copper plate. This, as will be 
seen, will turn the S0 4 ends towards the zinc, 
and the H 2 ends towards the copper. 

(3.) A decomposition of the polarized chain, 
whereby the S0 4 
unites with the zinc 
and the H 2 liberated f 




Fig. 2Q4. Conventionalized 
Molecule. 



reunites with the S0 4 

of the molecule next 

to it in the chain, and 

its liberated H 2 with 

the one next to it, and 

so on until the last liberated H 2 in the chain is 

given off at the surface of the copper or negative 

plate. This leaves the chain of molecules as 

shown at (3). 

(4.) A semi-rotation of the molecules of the 
chain, as at (3), until they assume the position 
shown at (4). This rotation is required, since all 
the molecules in (3) are turned with their similar 
poles towards similarly charged battery plates. 

Hypothesis, Single-Fluid Electric 

— (See Electricity, Single-Fluid Hypothe- 
sis of.) 

Hypothetical. — Of or pertaining to a hy- 
pothesis. 

Hypsometer. — An apparatus for determin- 
ing the height of a mountain or other eleva- 
tion by ascertaining the exact temperature at 
which water boils at such elevation. 

The use of a thermometer to measure the 
height of a mountain or other elevation is based 
on the fact that a given decrease in the tempera- 
ture of the boiling point of water invariably at- 
tends a given decrease in the atmospheric press- 
ure. Therefore, as the observer goes further 
above the level of the sea, the boiling point of 
water becomes lower, and from this decrease the 
height of the mountain or other elevation may be 
calculated, 

Hypsometrical. — Of or pertaining to the 
hypsometer. 

Hypsometrically. — In the manner of the 
hypsometer. 



Hysteresial Dissipation of Energy. — (See 
Energy, Hysteresial Dissipation of.) 

Hysteresis. — Molecular friction to mag- 
netic change of stress. 

A retardation of the magnetizing or de- 
magetizing effects as regards the causes 
which produce them. 

> The quality of a paramagnetic substance 
by virtue of which energy is dissipated on the 
reversal of its magnetization. 

The ratio of magnetic induction to the mag- 
netizing force producing it, or, in other words, 
the magnetic permeability, is greater when the 
magnetizing force is decreasing, than when it is 
increasing. This phenomenon is seen in the well 
known retention of magnetism in iron after the 
withdrawal of the force causing the magnetization, 
and was called by Ewing hysteresis, from 
'vdrepea), to lag behind. 

If a curve is constructed in which the hori- 
zontal abscissas represent the magnetizing force, 
or the magnetizing current to which they are 
proportional, and the vertical ordinates the 
number of lines of induction passing through the 
body that is being magnetized, both in the case 
of gradually increasing and gradually decreasing 
currents, the curve will be found to have greater 
values for the decreasing than for the increasing 
current. Constructing a curve in this manner for 
the case of a ring of 
iron, which has been 
first suddenly magnet- 
ized and then demag- 
netized, taking the 
magnetizing force along 
the line F H, Fig. 
295, and the result- 
ing magnetization 
along the line M N, a 
loop is formed in the 
curve, as shown in the 
figure. The arrows 
show the direction of Fig. 295. Curves of Hy 9- 
the magnetizing force ; teresis {Ewing). 

the shaded area the work done due to hysteresis. 

The area of this loop represents the amount of 
energy per unit of volume expended in perform- 
ing a magnetic cycle, i. e., in carrying the iron 
ring through a magnetization and subsequent 
demagnetiz ation. 

The physical meaning of the loop is that a lag- 




Hys.] 

ging of magnetization has occurred. This lag- 
ging of the magnetization is due to hysteresis. 
Ewing gives the value for the energy in ergs 
dissipated per cubic centimetre, for a complete 
magnetic cycle for a number of substances, as 
follows : 

Energy dissipated 
in ergs per cubic 
centimetre, during 
a complete c y cle of 
doubly reversed 
strong magnetiza- 
Sample of Iron operated upon. tion. 

Very soft annealed iron 9,300 ergs. 

Less soft annealed iron 16,300 " 

Hard drawn steel wire 60.000 " 

Annealed steel wire 70,500 " 

Same steel, glass hard 76,000 " 

Piano-forte steel wire, normal 

temper 116,000 " 

Same, annealed „ 94,000 " 

Same, glass hard 117,000 " 

Approximate^ 28 foot-pounds of energy are 
required to make a double reversal of strong 
magnetization in a cubic foot of iron. Energy 
expended in this way takes the form of heat. 
This heat, however, is to be distinguished from 
heat produced by Foucault currents. 

According to Ewing, hysteresis is greatly de- 
creased by keeping the iron in a state of mag- 
netic vibration. In this way, the energy dis- 
sipated in a complete magnetic cycle is corre- 
spondingly decreased. This observation of Ewing 
agrees with the prior observation of Hughes, who 
noticed that tapping or twisting a bar of ircin 
greatly accelerates the removal of its residual 
magnetism. 

The phenomena of hysteresis, according to 
Fleming, accounts for part of the energy which 
is dissipated in a dynamo-electric machine: 

(1.) In the field magnets. 

In an ordinarily constructed continuous- current 
dynamo, work is done in magnetizing the field 
magnets ; not only to give the iron its initial mag- 
netism, but also to constantly reproduce the mag- 
netism which the machine loses by reason of the 



273 



[Hys. 



continual vibrations to which it is subjected dur- 
ing its run. If sufficient residual magnetism 
were retained, on the withdrawal of the magneti- 
zing force there would be no necessity for the 
current in the field magnets ; but, since this is 
removed by even a small vibration, the energy of 
the exciting current must nee Is be expended. 

(2.) In the armature of the dynamo. 

The soft iron of the core is subjected to succes- 
sive magnetizations and demagnetizations. Ac- 
cording to Fleming, in the case of a core having 
a volume of 9,000 cubic centimetres, with fifteen 
reve.sals per second, the loss is equal to about ^ 
horse-power. 

Hysteresis, Static — ■ That quality in 

iron, or other paramagnetic substance, by 
virtue of which energy is dissipated during 
every reversal of its magnetization. 

Static hysteresis is so named in order to dis- 
tinguish it from viscous hysteresis. (See Hystere- 
sis, Viscous.) 

Hysteresis, Viscous The time-lag 

observed in magnetizing a bar of iron, 
which is referable neither to induction in the 
iron, nor to self-induction in the magnetizing 
current, but to the magnetic viscosity of the 
substance. 

A sluggishness exhibited by iron for mag- 
netization or demagnetization due to magnetic 
viscosity. 

The difference between static and viscous 
hysteresis is. thus stated by Fleming in consider- 
ing the analogous mechanical case of lifting a 
weight in a viscous fluid. "Apart from fluid 
resistance, the work done in lifting the weight 
against gravity, say one hundred times, is a hun- 
dred times the work required to be spent to lift 
it once ; but if fluid resistance comes into play, 
and if this varies as the square of the velocity of 
the moving body, then the total work done in 
lifting the weight through the fluid will be de- 
pendent also upon the rate at which the cycle is 
performed." 



Up.] 



274 



[111. 



I. H. P. — A contraction for indicated horse- 
power, or the horse-power of an engine as 
obtained by the means of an indicator card. 

I. W. G. — A contraction for Indian wire 
gauge. 

Idio-E lee tries. — A name formerly applied 
to such bodies as amber, resin or glass, which 
are readily electrified by friction, and which 
were then supposed to be electric in them- 
selves. 

This distinction was based on an erroneous 
conception, and the word is now obsolete. 

Idiostatic. — A term employed by Sir Wil- 
liam Thomson to designate an electrometer 
in which the measurement is effected by de- 
termining the repulsion between the charge 
to be measured and that of a charge of the 
same sign imparted to the instrument from 
an independent source. (See Heterostatic?) 

Idle Poles.— (See Poles, Idle.) 

Igniter, JaMochkoff A small strip 

of carbon, or some carbonaceous material 
that is readily rendered incandescent by the 
current, placed between the free ends of the 
parallel carbons of a Jablochkoff candle, for 
the establishment of the arc on the passage 
of the current. 

The igniter is necessary in the Jablochkoff elec- 
tric candle, since the parallel carbons are rigidly 
kept at a constant distance apart by the insulat- 
ing material placed between them, and cannot 
therefore be moved together as in the case of the 
ordinary lamp. (See Candle, Jablochkoff.) 

Ignition, Electric The ignition of 

a combustible material by heat of electric 
origin. 

The electric ignition of wires is generally ac- 
complished by electric incandescence. Ignition 
may be accomplished by the heat of the voltaic 
arc. (See Heat, Electric. Furnace, Electric.) 

The ignition of combustible gases is accom- 
plished by the heat of the electric spark. (See 
Burner, Automatic, Electric.) 

Illumination, Artificial The em- 
ployment of artificial sources of light. 



A good artificial illuminant should possess the 
following properties, viz.: 

(i.) It should give a generator uniform illumi- 
nation as distinguished from sharply marked 
regions of light and shadow. 

To this end a number of small lights well dis- 
tributed are preferable to a few large lights. 

(2.) It should give a steady light, uniform in 
brilliancy, as distinguished from a flickering, 
unsteady light. Sudden changes in the intensity 
of a light injure the eyes and prevent distinct 
vision. 

(3.) It should be economical, or not cost too 
much to produce. 

(4.) It sh mid be safe, or not likely to cause 
loss of life or property. To this intent it should, 
if possible, be inclosed in or surrounded by a 
lantern or chamber of some incombustible mate- 
rial, and should preferably be lighted at a dis- 
tance. 

(5 ) It should not give off noxious fumes or 
vapors when in use, nor should it unduly heat 
the air of the space it illumines. 

(6.) It should be reliable, or not apt to be un- 
expectedly extinguished when once lighted. 

The electric incandescent lamp is an excellent 
artificial illuminant. 

(1.) It is capable of great subdivision, and can, 
therefore, produce a uniform illumination. 

(2.) It is steady and free from sudden changes 
in its intensity. 

(3.) It compares favorably in point of economy 
with coal oil or gas, provided its extent of use is 
sufficiently great. 

(4.) It is safer than any known illuminant, 
since it can be entirely inclosed and can be 
lighted from a distance or at the burner without 
the dangerous friction match. 

The leads, however, must be carefully insu- 
lated and protected by safety fuses. (See Fuse, 
Safety. ) 

(5.) It gives off no gases, and produces far less 
heat than a gas-burner of the same candle power. 

It perplexes many people to understand why 
the incandescent electric light should not heat 
the air of a room as much as a gas light, since it 
is quite as hot as the gas light. It must be re- 
membered, however, that a gas-burner, when 
lighted, not only permits the same quantity of 



111.] 



275 



Imp. 



gas to enter the room which would enter it if 
the gas were simply turned on and not lighted, 
but that this bulk of gas is still given off, and is, 
indeed, considerably increased by the combina- 
tion of the illuminating gas with the oxygen of the 
atmosphere ; and, moreover, this great bulk of 
gas escapes as highly heated gases. Such gases 
are entirely absent in the incandescent electric 
light, and consequently its power of heating the 
surrounding air is much less than that of gas 
lights. 

(6.) It is quite reliable, and will continue to 
burn as long as the current is supplied to it. 

Illumination, Lighthouse, Electric 

— The application of the electric arc light 
to lighthouses. 

A powerful arc light is placed in the focus of 
the dioptric lens now commonly employed in 
lighthouses. Since the consumption of the carbon 
electrodes would alter the position of the focus of 
the light, electric lamps for such purposes are 
constructed to feed both of their carbons, instead 
of the upper carbon only, as in the case of the 
ordinary arc lamp. Such lamps are called focus- 
ing lamps. 

Illumination, Unit of A standard 

of illumination proposed by Preece, equal to 
the illumination given by a standard candle 
at the distance of 12.7 inches. 

According to Preece, the illumination of the 
average streets of London, where gas is employed, 
is equal to about one-tenth of this standard in the 
neighborhood of a gas lamp, and about one- 
fiftieth in the middle space between two lamps. 

The term unit of illumination, in place of in- 
tensity of light, was proposed by Preece in order 
to avoid the very great difficulty in determining 
the intensity of a light in a street or space where 
there were a number of luminous sources, and 
where the directions of incidence of the different 
lights vary so greatly. 

A carcel standard at the distance of a metre 
will illumine a surface to the same intensity of 
illumination as a standard candle at the distance 
of 12.7 inches. (See Candle, Foot.) 

Illumined Electrode.— (See Electrode, 
Illumined.) 

Imbibition Currents. — (See Currents, Im- 
bibition.) 

Images, Electric A term some- 



times applied to the charge produced on a 
neighboring surface by induction from a 
known charge. 

A positive charge produces, by induction, on a 
flat metallic surface near it, a negative charge 
which is distributed with varying density over the 
surface, but acts electrically as would an equal 
quantity of negative electricity placed back of the 
plate at the same distance the positive charge is 
in front of it. The correspondence of this charge 
with the image of an object seen in a plane mirror, 
has led to the term electric image. 

Maxwell defines electric image as follows: " An 
electric image is an electrified point, or system of 
points, on one side of a surface, which would pro- 
duce, on the other side of that surface, the same 
electrical action which the actual electrification of 
the surface really does produce." 

Impedance. — Generally any opposition to 
current flow. 

The sum of the ohmic resistance and the 
spurious resistance of a circuit measured in 
ohms. 

A quantity which is related to the strength 
of the impressed electromotive force of a sim- 
ple periodic or alternating current, in the same 
manner that resistance is related to the steady 
electromotive force of a continuous current. 

In the case of steady currents, the current 
strength is equal to the electromotive force di. 
vided by the resistance ; or, 

_, „ Electromotive force 

Current strength =■ 

Resistance. 

In the case of a simple periodic or alternating cur* 
rent, the average current strength is equal to the 
average impressed electromotive force divided by 
the impedance; or, 

Average current strength = 

Average impressed electromotive force 
Impedance. 

Since impedance, like true resistance of the cir- 
cuit, can be measured in ohms, it is sometimes 
called the virtual resistance. 

Impedance is a quantity equal to the square 
root of the sum of the squares of the inductive 
resistance of the circuit and the ohmic resistance. 

In the case of simple periodic or alternating 
currents, the average current strength is equal to 
the average impressed electromotive force, divided 
by the impedance ; the maximum current strength 



Imp. J 



276 



[IllCr 




is equal to the maximum impressed electromotive 
force, divided by the impedance. 

The impedance of a circuit can be repre- 
sented geometrically as fol- 
lows: Draw a right angled 
triangle (Fig. 296), the base 
of which represents the 
ohmic resistance of the cir- 

.. j , , j. 1 OHMIC RESISTANCE 

cuit, and the perpendicular, _ , _ J . , 

x Fig. 2go. Geometrical 

the inductive resistance; Re p resenta Hon of Im- 
then the hypothenuse will $edance. 
represent the impedance. 

Since the ohmic resistance equals R, and the in- 
ductive resistance equals the inductance L, mul- 
tiplied by 2 Tt n, in which n, is the frequency, the 
value of the impedance is equal to 
-/R 2 -|-4 7r 2 ns L'*, 

Impedance Coil. — (See Coil, Impedance) 

Impedance, Impulsive or Oscillatory 

The impedance which a conductor 

offers to an impulsive or oscillatory dis- 
charge. 

The impulsive impedance varies in simple pro- 
portion to the frequency of the periodic current. 
It depends on the form and size of the circuit, but 
it is independent of its resistance or permeability. 

Imponderable. — That which possesses no 
weight. 

A term formerly applied to the luminiferous 
or universal ether, but now generally aban- 
doned. 

It is very questionable whether it is possible for 
any form of matter to be actually imponderable 
or to possess no attraction for other matter. 

An imponderable fluid, as, for example, the 
universal ether, as the term is now generally em- 
ployed, is a fluid whose weight is comparatively 
small and insignificant, and not a fluid an infinite 
quantity of which would be entirely devoid of 
weight. 

Impressed Electromotive Force. — (See 
Force, Electromotive, Impressed.) 

Impulse, Electro-Magnetic -An im- 
pulse produced in the ether surrounding a 
conductor by the action of an impulsive dis- 
charge, or by a pulsating field. 

Impulse, Electromotive An im- 
pulse producing an impulsive rush of elec- 
tr'city. 



The term is employed to distinguish between) 
the ordinary electromotive force which produces a 
steady current of electricity and an electromotive 
impulse which produces an impulsive rush of elec- 
tricity or impulsive discharge. 

Impulsion Cell. — (See Cell, Impulsion) 

Impulsion Effect. — (See Effect, Impul- 
sion) 

Impulsive Impedance. — (See Impedance, 
Impulsive or Oscillatory) 

Incandesce. — To shine or glow by means, 
of heat. 

Incandescence. — The shining or glowing of 
a substance, generally a solid, by reason of a. 
sufficiently high temperature. 

Incandescence, Electric The shin- 
ing or glowing of a substance, generally a. 
solid, by means of heat of electric origin. 

Electric incandescence of solid substances differs 
from ordinary incandescence, in the fact that un- 
less the substance is electrically homogeneous 
throughout, the temperature is not uniform in all 
parts, but is highest in those portions where the 
resistance is highest and the radiation smallest. 

The deposition of carbon in and on a carbon 
conductor by the flashing process is quite different 
as performed by electrical incandescence, than it 
would be if the carbons were heated by ordinary 
furnace or other heat. (See Carbons, Flashing 
Process for.) 

Incandescence, Thermal The shin- 
ing or glowing of a substance, generally a 
solid, by means of heat other than that of 
electric origin. 

Incandescent. — Shining or glowing with 
heat. 

Incandescent Ball Electric Lamp. — (See 
Lamp, Electric, Incandescent Ball) 

Incandescent Electric Lamp, Life Curve 

of (See Curve, Life, of Incandescent 

Lamp) 

Incandescent Electric Lamp, Life of 

— (See Lamp, Electric, Incandescent, Life 
of.) 

Incandescent Straight Filament Lamp. 
— (See La7np, Incandescent, Straight Fila~> 
ment.) 



Inc. J 



277 



[Ind 



■Glowing or shining by 
means of heat. 

Inclination, Angle of The angle 

which a magnetic needle, free to move in a 
vertical and horizontal plane, makes with a 
horizontal line passing through its point of 
support. 

The angle of magnetic dip. 

A mignetic needle, supported at its centre of 
gravity, and capable of moving freely in a ver- 
tical as well as in a horizontal plane, does not 
retain a horizontal position at all parts of the 
earth's surface. 

The angle which marks its deviation from the 
horizontal position is called the angle of dip or 
inclination. (See Dij>, Magnetic.) 

Incandescent Electric Lamp. — (See 
Lamp, Electric, Incandescent.) 

Inclination Chart. — (See Chart, Inclina- 
tion.) 

Inclination Compass. — (See Compass, In- 
clination.) 

Inclination, Magnetic The an- 
gular deviation from a horizontal position of 
a freely suspended magnetic needle. (See 
Dip, Magnetic. Chart, Inclination.) 

Inclination Map. — (See Map or Chart, 
Inclination.) 

Inclination of Magnetic Needle. — (See 
Needle, Magnetic, Inclination of) 

Inclinometer. — A name sometimes given 
to an inclination compass. (See Compass, 
Inclination.) 

Incomplete Circuit. — (See Circuit, In- 
complete) 

Increased Electric Irritability.— (See 
Irritability, Electric, Increased) 

Increment Key. — (See Key, Increment) 

Increment Key of a Qiiadruplex Tele- 
graphic System. — (See Key, Increment, of 
Qiiadruplex Telegraphic System) 

India Rubber. — A resinous substance ob- 
tained from the milky juices of several tropi- 
cal trees. 

India rubber or caoutchouc is obtained from 
the Siphonia elastica of South America. 



India rubber is quite elastic and possesses high 
powers of electric insulation. When vulcanized 
or combined with sulphur, it still retains its 
powers of electric insulation in a high degree. 
In this state it is highly electrified by friction. 
(See Caoutchouc.) 

Indicating Bell. — (See Bell, Indicating) 

Indicator, Automatic Any auto- 
matic device for electrically indicating the 
number of times a circuit has been opened or 
closed, and thus the number of times a given 
operation has occurred which has caused the 
opening or closing of such circuit. 

An annunciator with an automatic drop is 
sometimes called an automatic indicator. (See 
Annunciator, Electro- Magnetic. Annunciator 
Drop, Automatic.) 

Indicator, Electric A name ap- 
plied to various devices, generally operated 
by the deflection of a magnetic needle, or the 
ringing of a bell, or both, for indicating, at 
some distant point, the condition of an electric 
circuit, the strength of current that is passing 
through it, the height of water or other liquid, 
the pressure on a boiler, the temperature, the 
speed of an engine or line of shafting, the 
working of a machine or other similar events 
or occurrences. 

A term sometimes used in place of annun- 
ciator. (See Annunciator, Electro-Magnetic) 

Indicators are of various forms. They are 
generally electro-magnetic in character. They 
are automatic in action. 

Indicator, Electric Circuit A de- 
vice, generally in the form of a vertical gal- 
vanometer, employed to indicate the presence 
and direction of a current in a circuit, and 
often to roughly measure its strength. (See 
Galvanometer, Vertical) 

Indicator, Electric, for Steamships 

— An electric indicator operated by circuits 
connected with the throttle valve and revers- 
ing gear of the steam engine. 

The signal "stop," for example, sent by the 
navigating officer to the engineer, causes him to 
close the throttle. This act places the indicator 
needle at "stop," and thus informs the officer 
that his signal has been obeyed. In the same 



Ind.] 



278 



[Ind. 



manner, the opening of the throttle sets the in- 
dicator needle to "ahead," etc. 

Indicator, Electric Throwback 



An annunciator with a drop that is electrically 
replaced. (See Annunciator, Electro-Mag- 
netic^) 

Indicator, Lamp —An apparatus 

used in the central station of a system of in- 
candescent lamp distribution to indicate the 
presence of the proper voltage or potential 
difference on the mains. 




Fig. 2QJ. Edisotl-Howett LamJ> Indicator. 

The lamp indicator of Edison and Howell is 
shown in Fig. 297. It consists essentially of a 
Wheatstone bridge with the resistances arranged 
as shown. A galvanometer at G, serves, by the 
movements of its magnetic needle, to act as an 
indicator. This needle remains at zero, when 
the potential difference is the exact voltage re- 
quired on the circuit with which the indicator is 
connected. The incandescent lamp at L, being 
one of the resistances, and being constantly 
traversed by the current, will have a fixed resist- 
ance for the temperature at which it is designed 
to run. The other resistances are so proportioned 
as to insure the needle at G, remaining at zero. 
If, however, the potential varies, the temperature 
of the lamp L, varies, and, being carbon, its re- 
sistance also varies, a rise of temperature cor- 
responding to a fall of lamp resistance, which 
destroys the balance of the bridge and deflects 
the galvanometer needle. The attendant then 
regulates the potential to bring the needle back to 
zero. 

Indicator, Mechanical Throwback 

— An annunciator with a mechanical drop. 
(See Annunciator, Electro-Magnetic. An- 
nunciator, Drop. Annunciator, Gravity.) 

Indicator, Pendulum An annun- 
ciator, the indicating - arm of which is operated 



by means of a pendulum. (See Annunciator, 
Pendulum.) 

Indicator, Potential An apparatus 

for indicating the potential difference between 
any points of a circuit. 

A voltmeter is a potential indicator. It is, 
however, more than an indicator, since it gives 
the value of the potential difference in volts. (See 
Voltmeter.) A lamp indicator is a potential in- 
dicator. (See Indicator, LamJ>.) 

Indicator, Semaphore An annun- 
ciator in which a gravity drop or shutter is 
caused to fall by the action of the electric 
current, thus exposing a number of other 
signals back of the drop or shutter. 

Indicator, Speed A name some- 
times applied to a tachometer. (See Tachom- 
eter?) 

A form of spetd indicator is shown in Fig. 
298. The endless screw drives the wheel when 
the triangular point is held firmly against the 
centre of the revolving shaft or pulley. 




Fig. 2q8. Speed Indicator. 

Indicator, Yoltaic Battery A de- 
vice for indicating the condition of a voltaic 
battery. 

Indifferent Point. — (See Point, Indif- 
ferent?) 

Indirect Excitation.— (See Excitation, 
Indirect?) 

Induced Atomic Currents.— (See Cur- 
rents, Induced, Atomic or Molecular?) 

Induced Current. — (See Current, In- 
duced?) 

Induced Direct Current. — (See Current, 
Direct, Induced?) 

Induced Electrostatic Charge. — (See 
Charge, Induced Electrostatic?) 

Induced Molecular Currents. — (See Cur- 
rents, Induced Molecular :) 



Ind.] 



279 



[Ind. 



Induced Reverse Currents. — (See Cur- 
rent, Reverse, Induced) 

Inductance The induction of a 

circuit on itself, or on other circuits. 

Self-induction. 

A term now generally employed instead of 
self-induction. 

That property in virtue of which a finite 
electromotive force, acting on a circuit, does 
not immediately generate the full current due 
to its resistance, and when the electromotive 
force is withdrawn, time is required for the 
current strength to fall to zero. — {Fleming) 

A quality by virtue of which the passage of 
an electric current is necessarily accompanied 
by the absorption of electric energy in the 
formation of a magnetic field. 

The inductance of a circuit depends: 

(i.) On the form or shape of the circuit. 

(2.) On the magnetic permeability of the space 
surrounding the circuit. 

(3. ) On the magnetic permeability of the circuit 
itself. 

For the variations of current strength in elec- 
tric circuits, inductance is not unlike mass, or 
moment of inertia, as regards variations of velo- 
city. Time is required to produce velocity in a 
heavy body by the action of any force; so also 
time is required to produce a current by the 
action of an electromotive force. 

The electro-magnetic energy present in any 
given current is equal to the square of the current 
multiplied by the inductance. Since one of these 
factors (the current strength) represents the 
force, the other, the inductance, must have the 
dimension of a distance or length. Inductance, 
therefore, is measurable in units of length. If 
the circuits are formed of magnetizable materials, 
the inductance of a circuit is the ratio between the 
total inductance taking place through the circuit 
to the current producing it. 

If the circuit is formed entirely of non-magnetic 
material, surrounded entirely by materials of 
constant magnetic permeability (such as air, in- 
sulators and diamagnetic materials generally), the 
inductance is a constant quantity and depends 
only on the form or shape of the circuit. In this 
case, the total inductance through the circuit is pro- 
portional to the magnetizing force, and the mag- 
netic resistance, or the magnetic conductance of 
the magnetic circuit, is equal to the total induc- 



tion through the circuit, divided by the magnetiz- 
ing force. 

In cases where the magnetic circuit is partly or 
wholly of paramagnetic substances, where the 
induction bears no constant ratio to the magnetiz- 
ing force, and where the induction takes place 
partly or wholly in media of variable permeability, 
the co-efficient of self- induction, or the inductance 3 
must be defined in three ways: 

(1.) As the ratio between the counter electro- 
motive force in any circuit and the time rate of 
variation of the current producing it. 

(2.) As the ratio between the total induction 
through the circuit and the current producing it. 

(3.) As the energy associated with the circuit 
in the form cf magnetic field, due to unit current 
in that circuit, or as the co-efficient by which half 
the square of the current must be multiplied to 
obtain the electro-kinetic energy of the circuit at 
that instant.— (Fleming.) 

A flat sheet or strip of metal possesses less in- 
ductance than a round conductor of equal cross- 
section. 

This may be explained by conceiving that a 
flat conductor presents a greater absorption sur- 
face to the dielectric. 

Therefore, the perfect form for a conductor 
transmitting rapidly alternating currents is that 
of a flat sheet or strip of copper, or preferably a 
copper tube. 

The experiments of Hughes show that the in- 
ductance of a conductor may be regarded as an 
effect due to the time required for the rapidly 
periodic current to penetrate the conductor and 
that the decrease in the inductance, produced by 
forming the conductor of a strip or bar, is due 
to the decreased distance the current has to pass 
to the inner parts. 

Inductance, Absolute Unit of A 

unit of length equal to one centimetre. 

A length equal to an earth quadrant or io 9 
centimetres is called the practical unit of induct- 
ance. The practical unit of inductance was form- 
erly called a secohm or quadrant. It is now gen- 
erally called a henry. (See Henry, A.) 

Inductance Bridge, — (See Bridge, In- 
ductance) 

Inductance, Co-efficient of A con- 
stant quantity, such that when multiplied by 
the current strength passing in any coil or cir- 
cuit, will represent numerically the induction 
through the coil or circuit due to that current. 



Ind. 



280 



rind* 



A term sometimes used for co-efficient of 
self-induction. (See Induction, Co-efficient 
of) 

Inductance, Constant — The induct- 
ance which occurs in circuits formed wholly 
of non-magnetic materials, immersed in or 
surrounded by media of constant magnetic 
permeability or magnetic conductance for 
lines of magnetic force. (See Permeability, 
Magnetic.) 

When the lines of magnetic force pass through 
such materials as ordinary insulators, or diamag- 
netic materials, such as copper, the inductance is 
constant, provided the geometric form of the cir- 
cuit remains the same. 

Inductance, Formal, of Circuit 



That part of the counter electromotive force 
of a circuit which depends on the form of the 
circuit. 

Inductance, or Self-induction, Practical 

Unit of A length equal to the earth 

quadrant or io° centimetres. 

The absolute unit of inductance is equal to I 
centimetre. 

Inductance, Oscillatory, Electric 

Inductance produced by electric oscillations. 

Inductance, Unit of A term now 

generally used for unit of self-induction. 

The value of the inductance may be given 
either in absolute or in practical units of induct- 
ance. The absolute unit of inductance is equal 
to a length of one centimetre. The practical unit 
of inductance is equal to 1,000,000,000 centi- 
metres or io'' centimetres. 

The practical unit of inductance was formerly 
called a secohm. The term henry is generally 
used for this unit. (See Henry, A.) 

Inductance, "Variable — — — The induc- 
tance which occurs in circuits formed partly 
or wholly of substances like iron or other 
paramagnetic substances, the magnetic 
permeability of which varies with the inten- 
sity of the magnetic induction, and where the 
lines of force have their circuit partly or 
wholly in such material of variable magnetic 
permeability. 

Induction. — An influence exerted by a 



charged body or by a magnetic field on neigh- 
boring bodies without apparent communica- 
tion. 

A medium is necessary to connect the body 
producing the induction and that in which the 
induction is produced. (See Induction, Electro- 
static. Induction, Magnetic. Induction, Electro- 
Dynamic. ) 

Induction, Apparent Co-efficient of 

— A term sometimes used for co-efficient of 
apparent magnetic induction. (See Indue- 
Hon, Magnetic, Apparent Co-efficient of.) 

It is called the apparent co efficient of induction 
because its value is different from what it would 
be if the eddy currents were entirely suppressed. 
The eddy currents increase the resistance of the 
primary and decrease its inductance. 

Induction-Balance, Hug-lies' (See 

Balance, Induction, Hughes .) 

Induction, Balance of, in Cable 

The removal of induction in a cable by 
neutralization by the presence of equal and 
opposite effects. 

A balance is obtained of the inductive effects of 
the neighboring conductors, whether in the 
bunched cable or outside of it. 

Induction-Bridge.— (See Bridge, I?iduc- 
tance.) 

Induction, Co-efficient of A term 

sometimes used for co-efficient of magnetic 
induction. (See Induction, Magnetic, Co- 
efficient of.) 

Induction Coil. — (See Coil, Induction) 

Induction Coil, Inverted — (See 

Coil, Induction, Inverted. Transformer) 

Induction, Current A term some- 
times used for voltaic induction. (See Induc- 
tion, Voltaic. Induction, Electro-Dynamic.) 

Induction, Dissymmetrical, of Armature 
An induction produced by the passage 



of a different number of lines of magnetic 
force through adjoining halves of the arma- 
ture. 

Induction, Electro-Dynamic -Elec- 
tromotive forces set up by induction in con- 
ductors which are either actually or practically 
moved so as to cut the lines of magnetic 
force. 



Ind.] 



281 



[Ind. 



These electromotive forces, when permitted to 
act through a circuit, produce an electric current. 

Electro-dynamic induction may be produced in 
any circuit in two ways: 

(i.) By causing expanding or contracting lines 
of magnetic force to pass through that circuit. 

(2.) By causing the circuit or conductor to pass 
through the lines of magnetic force. 

In all cases the lines of force are made to pass 
through the conductor or wire. 

There are four cases of electro-magnetic induc- 
tion: 

(I.) That in which expanding or contracting 
lines of magnetic force, produced by rapidly vary- 
ing the current in any circuit, are caused to pass 
through or cut that circuit and consequently to 
produce differences of potential therein. 

(2.) That in which expanding or contracting 
lines of magnetic force produced by any circuit by 
the rapidly varying strength of the electric 
current passing through that circuit, are caused 
to pass through another neighboring circuit and 
thus produce differences of potential therein. 

(3.) That produced by moving a conductor 
through a magnetic field so as to cut its lines of 
magnetic force. In this way the strength of the 
magnetic field may remain practically constant, 
but this strength as regards the field of the fixed 
conductor is varying, as the magnet producing 
such a field is moved toward or from such cir- 
cuit, and in this way differences of potential are 
produced in the circuit. 

(4.) That produced by moving an inducing field 
past a fixed conductor. This may Le accom- 
plished by moving an electro- magnet, an electric 
circuit, or a permanent magnet past the conductor 
in which the difference of potential is to be in- 
duced. 

There are therefore four distinct varieties of 
electro-dynamic induction: 

(1.) Self-induction or inductance. {See Induct- 
ance. ) 

(2.) Mutual induction, or, as it is sometimes 
called, voltaic current induction. (See Induction, 
Mutual. ) 

(3.) Electro-magnetic induction, or, as it is 
sometimes called, dynamo-electric induction. 

(4.) Magneto-electric induction. 

If the terminals of a voltaic cell be connected 
with the ends of a comparatively long coil of in- 
sulated wire, no appreciable spark will be observed 
on closing the cell, because the current induced 
by self-induction is in the opposite direction to the 



current of the cell and weakens it. On breaking 
contact, however, , a spark is readily observed. 
This is due to the induced current on breaking, 
which, flowing in the same direction as the cur- 
rent of the cell, strengthens it. 




Fig. 2QQ. Mutual Induction 

The coil B, Fig. 299, consists of two parallel 
coils of insulated wire, the terminals of one of 
which, called the primary coil, are connected 
with the battery cell P N, and those of the 
otner, called the secondary coil, with the galva- 
nometer G. 

Under these circumstances it is found: 

(1.) That at the moment of closing the circuit 
through the primary coil, a momentary current 
is produced in the secondary coil in a direction 
opposite to that of the current through the primary, 
as is shown by the direction of the deflection of 
the needle of the galvanometer. 

(2.) At the moment of breaking the circuit 
through the primary coll, an induced current is 
produced in the secondary coil in the same direc- 
tion as that flowing through the primary coil. 

(3.) These induced currents are momentary, 
and continue in the secondary only while the in- 
tensity of the current in the primary is varying, 
i. <?., while variations are occurring in the strength 
of the magnetic field in which the secondary coil 
is placed, therefore while the expanding or con- 
tracting lines of force are passing through the sec- 
ondary coil. 

If, for instance, when the current is established 
in the primary coil, and no current exists in the 




Fig- 300. Mutual Induction. 

secondary, the intensity of the current in the 
primary be varied by establishing a shunt circuit 
across the battery terminals, as by placing a short 
wire d, Fig. 300, in the mercury cups g, g, thus 



Ind.] 



282 



[Ind. 



decreasing the intensity of the current in the 
primary, an induced current will be set up in the 
secondary circuit in the same direction as the 
primary current. 

From all of these phenomena, we see that any 
increase of current in a conductor produces in a 
neighboring conductor an induced inverse current, 
or one in the opposite direction to the inducing 
current, while a decrease of such current produces 
a direct induced current, or one in the same 
direction as the inducing current. 

If the induction coil be made, as in Fig. 301, 
with its primary coil movable into and out of the 
secondary coil, then the following phenomena will 
occur: 

(1.) When the primary coil is moved toward 
the secondary cod an inverse current is induced 
in the secondary ; and, 

(2 ) When the primary coil is moved away from 
the secondary coil a direct current is induced in 
the secondary. 

The movements of permanent magnets towards 
or from a coil will also produce an induced cur- 
rent. 

If, for example, the apparatus be arranged as 
in Fig. 302, then: 



These facts may be expressed by the following 
laws : 
(1.) Any increase in the number of lines offeree 




Fig. 301. Electro-Dynamic Induction. 

(1.) A motion of the magnet towards the coil 
produces an induced current in the coil in one 
direction, and 

(2.) Its motion away from the magnet produces 
an induced current in the coil in the opposite 
direction. 

The directions of these induced currents are 
respectively inverse and direct as compared with 
the direction of the amperian currents which are 
assumed to produce the magnetic poles of perma- 
nent magnets, or of the currents that actually 
produce electro-magnets. (See Magnetism, Am- 
pere'' s Theory of.) 




Fig. 302. Magneto-Electric Induction. 

which pass through a circuit produces an inverse 
current in that circuit, while any decrease in the 
number of such lines of force which pass through 
any circuit produces a direct current in that 
circuit. 



OF CURRENT^ 
INDUCED &■ 




303. Fleming 's Rule. 



(2.) The intensity of the induced current, or, 
more correctly, the difference of potential pro- 
duced, is proportional to the rate of increase or 
decrease of the lines of force passing through the 
circuit. 

A conductor, therefore, when moved through 



iiid.] 



283 



[Ind. 



a magnetic field so as to cut the lines of magnetic 
force, will have a difference of potential generated, 
and if its circuit is closed so that the difference of 
potential can neutralize itself, it will have a cur- 
rent produced in it by induction. 

A simple but effective manner of remembering 
the direction of such currents is that proposed by 
Fleming. 

If the hand be held with the fingers extended, 
as in Fig. 303, and the direction of the forefinger 
represent the positive direction of the lines of 
force, i. e., those coming out of the N. pole of a 
magnet, then, if a wire or other conductor be 
moved in the direction in which the thutnb points, 
so as to cut these lines of force at right angles, 
that is, if the conductor have its length moved 
directly across these lines, it will have an induced 
current developed in it in the direction in which 
the middle finger points. (See Force, Lines of, 
Direction of. ) 

Or, the same thing can, perhaps, be even more 
readily remembered by 
cutting a piece of paper 
in the shape shown in ^ 
Fig. 304, marking it as g g 
shown, and then bending +> % 
the arm P, upward at the 8 § 
dotted line, so as to form p 
three axes at right angles 
to one another. ,_, 

As has been already 5 -g 
remarked, a difference of "•§ 2 
potential, and not a cur- 2 o 
rent, is produced by mov- 
ing a conductor through 
a magne;ic field so as to 
cut its lines offeree. 

It can be shown that in order to generate a dif- 
ference of potential of one volt, 100,000,000 C. G. 
S. lines of force must be cut per second. 

In electro-dynamic induction, the induced cur- 
rent is produced by the energy absorbed in moving 
the conductor through the magnetic field. Lenz 
has shown that in all cases of electro -dynamic 
induction, produced by the movement either of 
the circuit or of the magnet, the current induced 
in the circuit is in such a direction as to produce 
a magnet pole which would tend to oppose the 
motion. 

Induction, Electro-Magnetic A 

variety of electro-dynamic induction in which 
electric currents are produced by the motion 



Direction of 
Motion. 



M 



C 
Fig. 30 4. 



Fleming's Rule. 



of electro-magnets or electro-magnetic sole- 
noids. (See Induction, Electro-Dynamic) 

Induction, Electrostatic —The pro- 
duction of an electric charge in a conductor 
brought into an electrostatic field. 

If the insulated conductor A B, Fig. 305, be 
brought into the positive electrostatic field of the 
insulated conductor C, then, 

(1.) A charge will be produced on A and B, as 
will be indicated by the divergence of the pith 
balls. 

(2.) This charge is negative at the end A, 
nearest C, and positive at the end B, furthest 
from C, as can be shown by an electroscope. (See 
Electroscope. ) 





Fig. 3 OS- Electrostatic Induction. 

(3.) The charges at A and B, are equal to each 
other ; for, if the conductor A B, be removed from 
the field of C, without touching it, the opposite 
charges completely neutralize each other. 

(4.) If, however, the conductor A B, be touched 
at any place by a conductor connected with the 
earth, it will lose its positive charge, and will 
remain negatively charged when removed from 
the field of C. It is in this manner that an electro- 
phones is charged. (See Electrophones. ) 

(5.) The amount of the charges produced in the 
conductor, A B, can never be greater than that 
in the inducing body C. That is to say, the 




Fig. 306. Induction Precedes Attraction. 

negative electricity at A, may be sufficient in 
amount to neutralize the positive charge on C, if 
allowed to do so. In point of fact the charge in- 



Ind.] 



284 



[Ind. 



duced is less in amount than the inducing charge, 
according to the distance between C and A, and 
the nature and condition of the medium which 
separates them. 

The attraction? of light bodies by charged sur- 
faces are due to the opposite charge produced on 
those parts of th; light bodies that are nearest the 
charged body 

The pith ball B, Fig. 306, suspended by a silk 
thread between an insulated positively charged 
conductor A, and the uninsulated conductor C, 
will receive by induction a negative charge on 
the side nearest A, and a positive charge on the 
side nearest C. It is therefore attracted to A, 
where, receiving a positive cnarge, it is repelled to 
C, where it is discharged and again assumes a 
vertical position. Induction again occurs, and 
consequent attraction and repulsion. These 
movements follow one another so long as a suffi- 
cient charge remains in A. 

Induction, Faradic, Apparatus 

(See Apparatus, Faradic Induction.) 

Induction-Finder. — (See Finder, Indue- 
tion.) 

Induction, Lateral — An induction 

observed between closely approacned portions 
of a circuit through which an impulsive dis- 
charge, such as the disruptive discharge of a 
Leyden jar, is passed as along spark, thereby 
making the resistance of the circuit high. 

A long copper wire, bent in the form of a rec- 
tangle, has its free ends near their extremities 
bent so as to approach within half an inch of each 
other. One of the ends of the wire is provided 
with a metallic ball and the other end connected 
with the earth. If, now, a Leyden jar charge is 
passed through the wire by connecting the outer 
coating with the end of the earth-connected wire 
and holding the inside coating near the knob, a 
spark will pass through the half inch of space be- 
tween the approached portions of the circuit. 

This discharge is due to what was formerly 
called lateral induction. The discharge of a 
Leyden jar is an oscillatory discharge, and it 
passes through the intervening air space instead 
of through the conductor because the resistance 
of the latter to the rapid alternations produces a 
counter electromotive force which acts as a re- 
sistance whose value is greater than that of the 
air space itself. (See Path, Alternative.) 



Induction, Magnetic 



-The produc- 



tion of magnetism in a magnetizable substance 
by bringing it into a magnetic field. 

Suppose a small portion of a magnetizable body 
is placed in a magnetic field produced in a gap 
separating two closely approximated poles. To 
simplify matters, suppose this small portion to be 
a free unit pole. It will be acted on by two 
forces : 

(1.) The force due to the magnetic field. 

(2.) The force dae to the free magnetism, 
which appears at the surface of the gap or cut. 

The force on the unit pole is compounded of 
these two separate forces, and is called the magnetic 
induction of the space. Magnetic induction is, 
therefore, strictly speaking, a quantity. 

The direction of magnetic force and the mag- 
netic induction are the same in an air space out- 
side a magnet. Within a bar of iron or other 
paramagnetic material, under induction in a mag- 
netic field, the magnetic force at any point is due 
not only to the external or original field, but also 
to the field produced by the polarity induced, 
which acts opposed to the magnetic force at 
points. Magnetic force and magnetic induction 
are identical only where there is no magnetism. — 
{Fleming.) 

When a magnetizable body is brought into a 
magnetic field the following phenomena occur, 
viz.: 

(1.) The lines of magnetic force pass through 
the body and are condensed upon it. (See Field, 
Magnetic. Paramagnetic. ) 

(2.) If the body is free to move around an axis, 
but is not free to move bodily towards the magnet 
pole, it will come to rest with its greatest extent 
or length in the direction ol the lines of force; 
i. e., in the direction in which it will offer the 
least resistance to the lines oi force that thread 
through it. 

(3. ) The body will therefore become a magnet, 
its south pole being situated where the lines of 
force enter it and its north pole where they pass 
out from it. Since the lines of magnetic force 
are assumed to come out of the north pole of a 
magnet and to enter its south pole, if a magnet- 
izable substance is brought near a north pole, 
the lines of force from that north pole will enter 
it at those parts nearest such north pole, thereby 
rendering such points south, and will pass out of 
its further end, which will thereby become north. 

(4.) The intensity of the induced magnetism 



Ind.] 



285 



[Ind. 



will depend on the number of lines of force that 
pass through it. 

(5 . ) The direction of the axis of magnetization 
will depend on the directions in which the lines 
of force thread through the body. (See Axis y 
Magnetic.) 




N S N' 5' 

Fig, 307. Magnetic Induction. 

If abarofiron, N' S ,Fig. 307, be brought near 
the magnetized bar, N S, poles will be produced 
in it by induction, as may be shown by throwing 
iron filings on it. 

The nearer the body to be magnetized is brought 
to the magnetizing pole the greater will be -the 
number of lines of force that thread through it. 
Consequently, the intensity of the induced mag- 
netism will be greater ; this will be greatest when 
the bodies actually touch each other. 

The production of mag/ietis7)i, therefore, by 
co7itact or touch is only a special case of the pro- 
ductio/i of 77iag7ietizatio7i by induction. 

The attraction of a magnetizable body by a 
magnet pole is caused by the mutual attraction 
which exists between the pole produced by induc- 
tion and the pole producing the induction. This, 
it will be seen, is similar to the attraction caused 
by an electric charge. 

The following terms are given by Fleming as 
employed in the same sense as magnetic induc- 
tion of an area: 

(i.) The number of unit tubes of induction 
passing through the area. 

(2.) The number of lines of force (induction) 
passing through the area. — {Faraday.) 

(3.) The total magnetic induction through the 
area. — {Maxwell. ) 

(4.) The flux or flow of magnetic induction 
through an area. — {Mascart &> Joabert.) 

(5.) The surface-integral of magnetic induction 
over an area. — {Fle77iing.) 

Induction, Magnetic, Apparent Co-effi- 
cient of The co-efficient of induction 

as influenced by the presence of eddy cur- 
rents. 

This is called the co-eflicient of apparent in- 
duction, because its value is not the same as it 
would be if the eddy currents were entirely sup- 
Dressed. 



The value of the co-efficient of apparent induc- 
tion depends on the amount of the retardation of 
the magnetism; or, what is the same thing, on 
the strength of the eddy currents. 

Induction, Magnetic, Co-efficient of 

— A term sometimes used instead of magnetic 
permeability. (See Per?neability, MagJietz'c.) 

The ratio existing between the number of 
lines of magnetic induction that pass through 
any area of cross-section of a magnetic cir- 
cuit and the magnetizing force producing 
such induction. 

If B, equals the magnetic induction, or the num- 
ber of lines of force that pass through any area of 
cross- section, and H, equals the magnetizing force, 
and ju, equals the permeability, or the co-efficient 
of magnetic induction; then, 

B 
M= K ' 

Induction, Magnetic, Dynamic - 

The induction which takes place in the field 
of a magnet whose field is moving as regards 
the body in which induction is occurring. 

This movement of the field may be attained, 

(1.) By the movement of the magnet. 

(2.) By the movement of the body in which 
induction is taking place. 

(3.) By the expansion or contraction of the lines 
of magnetic force produced by variations of the 
strength of the magneti c field ; or, in other words, 
by the movement of the field. (See Induction, 
Electro - Dyna77iic .) 

Induction, Magnetic, Flux or Flow of 

A term employed in the same sense 

as the magnetic induction which takes place 
through any given area. 

The flux or flow of magnetic induction is equal 
to the magnitude of the area multiplied by the 
normal induction which takes place in one unit 
of that area. 

Induction, Magnetic, Lines of 

Lines which show not only the direction in 
which magnetic induction takes place, but 
also the magnitude of the induction. 

A line of induction may be regarded as a line 
along which induction takes place, or as the axis 
of a tube of induction. 

This term is often loosely used for lines of force. 

Induction, Magnetic, Static The 



Ind.] 



286 



[Ind. 



induction which takes place in the field of a 
magnet whose field is stationary as regards 
the body in which induction is occurring. 

The term static magnetic induction is used in 
contradistinction to dynamic magnetic induction 
which occurs in a moving field. (See Induction, 
Electro-Dynamic. ) 

Induction, Magnetic, Surface-Integral 

of A term employed in the same sense 

as the magnetic induction which takes place 
over a given area. 
Induction, Magneto - Electric A 

variety of electro-dynamic induction in which 
electric currents are produced by the motion 
of permanent magnets, or of conductors past 
permanent magnets. (See Induction, Elec- 
tro-Dynamic?) 

Induction, Mutual Induction pro- 
duced by two neighboring circuits on each 
other by the mutual interaction of their mag- 
netic fields. (See Induction, Electro-Dy- 
namic. Currents, Extra?) 

Induction produced in neighboring charged 
conductors by the mutual interaction of their 
electrostatic fields. (See Field, Electro- 
static?) 

The mutual induction of two conductors or cir- 
cuits, is equal to the ratio of the induction which 
takes place through one of the circuits, to the 
strength of current in the other circuit, which is 
producing the induction 

Induction, Mutual, Co-efficient of 

The quantity which represents the number 
of lines of force which are common to or 
linked in with two circuits, which are pro- 
ducing mutual induction on each other. 

The maximum value the co-efficient of mutual 
induction can have, is equal to the square root of 
the product of the inductance of the two circuits, 
or y'L X N, in which L and N, are the constant 
co-efficients of self-induction of the two circuits. 

Induction, Mutual, Loops of Loops 

or lines of induction produced in any circuit 
by variations in the intensity of the current 
flowing in a neighboring circuit. 

The lines of induction produced by a circuit, in 
which a current of electricity is flowing, are 
closed loops or circles surrounding the circuit 
once or more. The wire or circuit is formed by 



coiling a conductor a number of times in a cir- 
cular coil, and this circular coil is placed near" 
another coil in which a varying current is flowing. 
As the lines of induction grow or increase, 
they cut the circular coil, forming lines of induc- 
tion in the shape of loops, a number of which pass ; 
around it„ They are called loops of mutual in- 
duction. 

Induction, Open-Circuit The in- 
duction produced in an open circuit by means 
of electric pulses in neighboring circuits. 

The researches of Hertz have shown that when 
an impulsive discharge, or an oscillatory dis- 
charge, occurs, an induction occurs even in open 
circuited conductors. He shows that these induc- 
tive effects are due to electro-magnetic waves or 
oscillations set up in the surrounding ether, 
which are propagated through free ether with the: 
velocity of light. When these electro-magnetic 
waves or radiations impinge on any circuit, if its 
dimensions be such that sympathetic vibrations^ 
can be excited therein, such vibrations are set up 
and cause similar phenomena to those of the ex- 
citing cause, viz., oscillatory discharges or elec- 
tro-magnetic vibrations. Hertz calls these sym- 
pathetic circuits, resonators, from their resem- 
blance to acoustic resonators. (See Resonators, 
Electric.) 

Induction, Oscillatory A name 

sometimes applied to open-circuit induction.. 
(See Induction, Open-Circuit?) 

Induction, Reflection of A term 

proposed by Fleming to express an action 
which resembles a reflection of inductive 
power. 

The coils A and B, Fig. 308, are arranged as 




I'l'l 

Fig. 308. Reflection of Induction. 

shown, so as to act as the primary and secondary 
respectively of an induction coil, and are placed 



lad.] 



287 



[Ind. 



conjugate or perpendicular to each other. (See 
Coils, Conjugate.) Therefore, no sounds are 
heard in the telephone T, when the current is 
rapidly reversed. If, however, a plate of copper, 
C, is placed in the position shown, then sounds 
are heard in the telephone. The action here 
resembles a reflection of the inductive action from 
A to B, by means of the plate C. The explana- 
tion is, of course, simple. Though A, can exert 
no action on B, because the two coils are conju- 
gate to each other, yet A, can produce secondary 
currents in C ; and these reacting on B, produce 
tertiary currents in C, and, therefore, sounds in 
the telephone. 



Induction, Self 



-Induction produced 



in a circuit at the moment of starting or stop- 
ping the currents therein by the induction of 
the current on itself. (See Currents, Extra.) 
A coil having unit self-induction, is sometimes 
said to have one tube of induction, or line of force 
added to its field for each increase of one unit of 
current. 

Induction, Self, Absolute Unit of 

A term sometimes employed for absolute unit 
of inductance. (See Inductance, Absolute 
Unit of.) 

Induction, Self, Ayrton & Perry's 
Standard of A standard for the com- 
parison of values of self-induction. 

The standard of self-induction of Ayrton & 
Perry consists of three bobbins of wire, two fixed 
and one movable. The movable bobbin is so ar- 
ranged as to be capable of motion through 180 
degrees within the fixed bobbins. The coils are 
wound on the surface of the zone of a sphere. 

This apparatus permits of the ready compari- 
son of the self-induction in different circuits, or in 
the same circuit under different conditions. 

Induction, Self, Co-efficient of — 

The number of lines of force the current would 
induce or enclose in itself when the current 
flowing through it is equal to one absolute 
unit. 

A term sometimes employed in the sense 
of inductance of a circuit. 

The co-efficient of self-induction is defined by 
Fleming as follows : "In the case of circuits con- 
veying electric currents, which are wholly made 
of non-magnetic material, and wholly immersed 



in a medium of constant magnetic permeability, 
the total induction through the c'.rcuit per unii of 
current flowing in that circuit, when removed 
from the neighborhood of all other magnets and 
circuits, is called the co-efficient of self- induction; 
otherwise the ratio of the numerical values of the 
electro-magnetic momentum of such circuit, and 
the current flowing in it, when totally removed 
from all other currents and magnets, is the nu- 
merical value of the inductance of the circuit." 

Since the magnetic lines due to a current in a 
circuit thread through the convolutions of the cir- 
cuit itself, any variation in the current induces 
a difference of potential in the circuit itself, since 
the lines of force produced by the current in the 
circuit pass through or cut the circuit. 

The ratio between this self-induced electromo- 
tive force, and the rate of change in the current 
which causes it, is called the co-efficient of self- 
induction.- (S. P. Thompson.) 

For a given coil the co- efficient of self-induction 
is, according to S. P. Thompson : 

( i . ) Proportional to the square of the number 
of convolutions. 

(2.) Is increased by the use of an iron core. 

(3.) If the magnetic permeability is assumed as 
constant, the co-efficient of self-induction is nu- 
merically equal to the product of the number of 
lines of magnetic force due to the current, and 
the number of times they are enclosed by the 
circuit. 

Induction, Self, Magnetic —A re- 
tardation in the appearance of magnetization, 
after the application of the magnetizing force, 
due to the influence of the magnetic lag. 

Magnetic retardation. 

This retardation in the magnetization has re- 
ceived the name of magnetic self-induction or re- 
tardation because it corresponds to the retarda- 
tion in the starting or stopping of a current, in a 
conducting circuit, due to the self-induction of the 
current. 

Induction, Self, Unit of The unit 

of inductance. (See Inductance, Unit of.) 

The unit of self-induction is now generally 
called the unit of inductance. 

Induction, Symmetrical, of Armature 

An induction produced by the simul- 
taneous passage of the same number of lines 
of magnetic force through adjoining halves of 
the armature. 



Ind.] 



288 



[lnd. 



Induction Telegraphy, Current Induc- 
tion System of (See Telegraphy, In- 
duction, Current Induction System of.) 

Induction Telegraphy, Static Induction 
System of • — (See Telegraphy, Induc- 
tion, Static Induction System of.) 

Induction Top. — (See Top, Induction.) 

Induction, Total Magnetic —The 

total magnetic induction of any space is the 
number of lines of magnetic induction which 
pass through that space, where the magnetiz- 
able material is placed, together with the lines 
added by the magnetization of the magnetic 
material. 



Induction, Tubes of 



-A portion of 



a magnetic field containing a number of 
closely contiguous lines of induction termi- 
nated by equipotential surfaces, or surfaces 
perpendicular to the lines of induction. 

Tubes of induction possess the following char- 
acteristics : 

(I.) The product of a normal cross-section of a 
tube and the mean magnetic induction which 
takes place over that section is the same for all 
cross-sections of the tube. In other words, the 
flux or flow of induction is constant throughout 
the entire length of the tube. 

(2.) The normal cross-section of any equipoten- 
tial surface at any point of a tube of induction is 
inversely proportional to the magnetic induction 
at that point. 

(3.) All tubes of induction form endless tubes. 
This is necessary, since all lines of induction form 
closed circuits. 

(4.) All tubes of induction may be expressed 
by a single line of induction, which, in the case of 
a uniform field, occupies the centre of the tube. 
(See Force, Tubes of.) 

Induction, Toltaic A variety of 

electro-dynamic induction produced by cir- 
cuits on themselves or on neighboring circuits. 

Mutual induction. (See Induction, Elec- 
tro-Dyna7nic.) 

This kind of induction is usually called current 
induction. 

Induction, Unipolar A term some- 
times applied to the induction that occurs 
when a conductor is so moved through a 



magnetic field as to continuously cut its lines 
of force. 
If the conducting wire, ABC, Fig. 309, be ro- 




Fig'- 30Q. Unipolar Induction. 
tated (in a direction toward the observer) around 
the pole N, of a magnet, it will continuously cut 
its lines of magnetic force in practically the same 
direction, and will therefore produce a difference 
of potential that will result in a continuous cur- 
rent in the direction of the arrows. The end A, 
is supported in a recess in N, while the end near 
C, slides on a projection on the middle of the 
magnet. 

Unipolar induction occurs in the case of Stur- 
geon's wheel, in which a metallic disc mounted 
on an axis is rotated between the poles of a mag- 
net so as to cut the lines of magnetic force. In 
this case a difference of potential is generated 
which will produce a current that flows from the 
axis to the periphery, provided contact points are 
placed on the axis of rotation and the periphery 
of the disc connecting these parts of the disc in a 
closed circuit. 

Unipolar dynamos operate by the continuous 
cutting of lines of magnetic force. 

Strictly speaking, there is no such thing as a 
unipolar dynamo or unipolar induction, since a 
single magnetic pole cannot exist by itself. Con- 
tinuous cutting of lines of magnetic force, how- 
ever, can exist, and produces, unlike the ordinary 
bipolar induction, a continuous current without 
the use of a commutator. 

Inductionless Resistance. — (See Resist- 
ance, Inductionless.) 

Inductive Capacity, Specific (See 

Capacity, Specific Inductive.) 

Inductive Circuit. — (See Circuit, Induc- 
tive?) 



Ind.J 



289 



[Ine. 



Inductiye Electromotive Force. — (See 
Force, ElectrojJiotive, Inductive.) 

Inductive Retardation. — (See Retarda- 
tion, I?iductive.) 

Inductive Resistance. — (See Resistance, 

Inductive.) 

Inductivity, Specific Magnetic ■ 

A term sometimes employed for specific mag- 
netic conductivity. (See Conductivity, Spe- 
cific Magnetic.) 

Inductometer, Differential — An 

apparatus for measuring, by means of a gal- 
vanometer, the momentary currents produced 
by the discharge of a cable. 

Currents produced by the discharge of a cable 
are of so short a duration that they do not pro- 
duce much more than a momentary effect on a 
galvanometer needle. 

The inductive charge in a cable, or the quan- 
tity of electricity produced in it by induction, is: 

(i.) Directly as the electromotive force of the 
charging battery; 

(2.) Inversely as the square root of the thick- 
ness of the coating of gutta-percha or other insu- 
lating material between ihe conducting wires and 
the metallic sheathing; 

(3.) Directly as the square root of the diameter 
of the copper wire of the conductor; and 

(4.) Dependent on the specific inductive capa- 
city of the insulating material employed in the 
cable. 

In order to cause the cable discharge to more 
thoroughly affect the galvanometer needle, Mr. 
Latimer Clark employed a differential instrument 
with a large battery and three reversing keys, by 
means of which he gave a rapid succession of 
charges to the cable. He called the instrument a 
Differential Inductometer. 

Induetophone.— A device, suggested by 
Mr. Willoughby Smith, for obtaining electric 
communication between moving trains and 
fixed stations by means of the currents devel- 
oped by induction in a spiral of wire fixed on 
the moving engine, by its motion past spirals 
on the line, into which intermittent currents 
are passed. 

The spiral on the engine is p'aced in the circuit 
of a telephone. (See Telezrabh . Inductive.} 



Inductor Dynamo. — (See Dyna?no, Induc- 
tor.) 

Inductorium. — A name sometimes applied 
to a Ruhmkorff induction coil. (See Coil, 
Induction) 

Inequality, Annual, of Earth's Magnetic 

Tariation or Inclination Annual 

variations in the value of the magnetic varia- 
tion or inclination at any place. (See Varia* 
tioji, Magnetic. Inclination, Magnetic?) 

Inequality, Annual, of Earth's Magnet- 
ism Variations in the value of the 

earth's magnetism during the earth's revolu- 
tion depending on the position of the sun. 

Annual variations in the earth's magnetism. 
(See Variations, Magnetic, Annual,) 

Inequality, Diurnal, of Earth's Magnetic 

Variation or Inclination — Diurnal 

variations in the value of the earth's magnetic 
variation or inclination. (See Variation, 
Magnetic. Inclination, Magnetic) 

Inequality, Diurnal, of Earth's Magnet- 
ism Inequalities or variations in the 

value of the earth's magnetism, dependent on 
the position of the sun during the earth's 
rotation. 

Inequality, Lunar, of Earth's Magnetic 
Tariation or Inclination Small va- 
riations in the value of the magnetic variation 
or inclination, dependent on the position of 
the moon as regards the magnetic meridian. 

Inequality, Lunar, of Earth's Magnet- 
ism Small variations in the value of 

the earth's magnetism dependent on the po- 
sition of the moon as regards the magnetic 
meridian. 

Inertia. — The inability of a body to change 
its condition of rest or motion, unless some 
force acts on it. 

The inertia of matter is expressed in Newton's 
first law of motion, as follows ; 

"Every body tends to preserve its state of rest 
or of uniform motion in a straight line, except in 
so far as it is acted on by an impressed force. ' ' 

All matter possesses inertia. 

Inertia, Electric A term some- 
times employed instead of electro-magnetic 
inertia. (See Inertia, Electro-Magnetic!) 



Ine.] 



290 



[Ins. 



A term employed to indicate the tendency 
of a current to resist its stopping or starting. 

By self-induction an electromotive force is pro- 
duced in a wire or other conductor at the moment 
of starting the current in it that tends to oppose 
the starting of such current, and also an electro- 
motive force at the moment of stopping the cur- 
rent, in such a direction as to prolong or continue 
the current. In other words, self induction tends 
to retard the rise or fall of the current. 

Fleming traces the following comparison be- 
tween the moment of inertia of a rotating wheel 
and the energy of its rotation on the one side, and 
the inductance of a circuit and the electro-mag- 
netic energy of the circuit on the other. 

(i.) The angular momentum of a fly-wheel is 
equal to the numerical product of its moment of 
inertia and the angular velocity of the wheel. 
Similarly the electro-magnetic momentum is equal 
to the product of the inductance of the circuit by 
the current flowing through it at any instant. 

(2.) The rate of change of the angular mo- 
mentum of the wheel, at any instant, is a measure 
of the rotational force of the couple acting at that 
instant. 

Similarly the rate of change of the electro-mag- 
netic momentum of the circuit is the measure of 
the electromotive force acting on it so far as 
mere change of current is concerned, and irre- 
spective of that part of the electromotive force re- 
quired to overcome the ohmic resistance. 

An electric current does not start or stop in- 
stantaneously. It requires time to do either, just 
as a stream of water or other fluid does, and it is 
this property which is referred to by the term 
electric inertia. Inertia does not appear to be 
possessed by electricity apart from matter. " It 
is doubtful," says Lodge, "whether electricity 
of itself, and disconnected from matter, has any 
inertia." 

Inertia, Electro-Magnetic A term 

sometimes employed instead of inductance, 
or the self-induction of a current. (See In- 
ductance. Inertia, Electric?) 

Inertia, Electro-Magnetic, Co-efficient of 

A term sometimes employed in place 

of the co-efficient of inductance or self-induct- 
ance of a circuit. 

Inertia, Magnetic The inability of 

a magnetic core to instantly lose or acquire 
magnetism. 



A magnet core tends to continue in the mag- 
netic state in which it was placed. 

The magnetic inertia is sometimes called the 
magnetic lag. 

To decrease the magnetic inertia, the strength 
of the magnetizing current is increased and the 
length of the iron core decreased. The iron 
should also be quite soft. (See Lag, Magnetic. 
Force, Coercive.} 

Inferred Zero.— (See Zero, Inferred) 

Infinity Plug.— (See Plug, Infinity.) 

Influence. — A term sometimes used instead 
of electrostatic induction. (See Induction, 
Electrostatic) 

The word influence is used by some to apply 
t ) the case of electrostatic induction, as distin- 
guished from electro-magnetic or magnetic induc- 
tion. 

Influence Charge.— (See Charge, Influ- 
ence) 

Influence Machine. — (See Machine, In- 
fluence) 

Inker, Morse — A form of tele- 
graphic ink-writer. (See Ink- Writer, Tele- 
graphic) 

Ink- Writer, Telegraphic A device 

employed for recording the dots and dashes 
of a telegraphic message in ink on a fillet or 
strip of paper. 

A telegraphic ink- writer is a form of telegraphic 
recorder. (See Recorder, Morse.) 

Inside Wiring. — (See Wiring, Inside) 

Insolation, Electric A term some- 
times employed for electric sunstroke, or 
electric prostration. (See Sunstroke, Elec- 
tric. Prostration, Electric) 

Installation. — A term embracing the 
entire plant and its accessories required to 
perform any specified work. 

The act of placing, arranging or erecting 
a plant or apparatus. 

Installation, Electric The estab- 
lishment of any electric plant. 

An electric light installation, for example, in- 
cludes the steam engine and boilers, or other 
prime movers, the dynamo-electric machines, the 
line wires or leads, and the lamps. 

Insulated Body. — (See Body, Insulated) 



Ins.] 



291 



[Ins. 



Insulating Cements. — (See Cements, In- 
sulating^) 

Insulating Sleeve.— (See Sleeve, Insula- 
ting) 

Insulating- Stool.— (See Stool, Insula- 
ting) 

Insulating- Tape.— (See Tape, Insula- 
ting) 

Insulating- Tuoe. — (See Tube, Insula- 
ting) 

Insulating- Tarnish. — (See Var7iish, Elec- 
tric) 

Insulation, Electric Non-conduct- 
ing' material so placed with respect to a con- 
ductor as to prevent the loss of a charge, or 
the leakage of a current. 

In the case of coils the character of the insula- 
tion of the coil of wires through which the cur- 
rent is to pass must be considered from the stand- 
point of the cooling of the coil by radiation. 

In considering the safest and most economical 
current density to employ in any dynamo or 
motor, the depth of the coil, i. e., the thickness of 
its coils, must be considered, as well as the char- 
acter of the materials employed for the insulation. 
Such substances as silk or wool, which are char- 
acterized by low heat conduction, retain the heat 
longer than cotton. Hence the depth of a silk 
covered coil should necessarily be less than that of 
one covered with cotton. 

Insulation Joint. — (See Joint, Insula- 
tion) 

Insulation, Porous An insulating 

material containing air or gas placed between 
the conductor and the insulating covering. 

A strip of perforated paper is used for cover- 
ing the bare conductor, and the insulating ma- 
terial is placed on the outside of this ; or, a cord 
is wrapped separately around the conductor, and 
the insulating material is placed on the outside of 
this. By these means, as will be seen, a layer of 
air exists between the conductor and its insulating 
covering. 

Insulation Eesistance. — (See Resistance, 
Insulation) 

Insulation, Static — A term em- 
ployed in electro-therapeutics for a method 
of treatment by convection streams or dis- 



charges, in which the patient is seated on an 
insulated stool connected to one pole or 
electrode of an influence machine, while the 
other pole or electrode is connected to the 
ground. 

Insulator Cap. — (See Cap, Insulator) 

Insulator, Dice-Box A name some- 
times applied to a double-cone insulator. (See 
Insulator, Double-Cone) 

Insulator, Douhle-Cone An insu- 
lator in which the line wire passes through and 
is supported by means of a tube consisting of 
two inverted cones joined at their smaller 
bases. 

Insulator, Double-Cup An insula- 
tor consisting of two funnel-shaped cups, 
placed in an inverted position on the sup- 
porting pin and insulated from one another 
by a free air space, except near the ends, 
which are cemented. 

The wire is wrapped in a groove on the outside 
of the outer cup. This possesses the advantage 
of exposing it to the rain, which thus cleanses the 
insulator and improves its power of insulation. 
The inner cup is supported on a pin and the outer 
cup cemented to it. Any leakage must, there- 
fore, pass over the entire surface of bjih cups. 

Insulator, Double-Shackle A form 

of insulator used in shackling a wire, consist- 
ing of two single-shackle insulators. 

Insulator, Double-Shed A double- 
cup insulator. (See Insulator, Double-Cup) 

Insulator, Fluid An insulator pro- 
vided with a small, internally placed, annular, 
cup-shaped space, filled with an insulating 
oil, thus increasing the insulating power of the 
support. 

The line wire is wrapped in a groove on the 
outside of the insulator. Any surface leakage 
between the wire and ground in wet weather 
must occur between the outer surface of the insu- 
lator, which is kept cleansed by the rain, and the 
inner surface, where it is supported by the pin. 
But to do this, the current must cross the oil in 
the cup, which, from its high power of insulation, 
effectually prevents leakage. 

Insulator, Invert — An insulator 



Ins.] 



292 



[Int. 



placed on the top of the wire instead of under- 
neath it, as was formerly done. 

Insulator, Oil — A fluid insulator 

filled with oil. (See Insulator, Fluid.) 

Insulator Pins. — (See Pins, Insulator) 

Insulator, Single-Shackle A form 

of insulator used for shackling a wire. (See 
Shackling a Wire) 

Insulator, Single-Shed An insula- 
tor with a single inverted cup. 

The wire is wrapped around a groove on the 
outside of the cup, where it is exposed to the 
cleansing action of the rain. The cup is inverted 
and supported on a pin, to which it is screwed and 
cemented. 

Insulator, Telegraphic or Telephonic 
A non-conducting support of tele- 
graphic, telephonic, electric light or other 
wires. 

Insulators are generally made of glass, earthen- 





Fig. 3 to. Glass 
Insulator. 



Fig. j 1 1. Porcelain 
Insulator. 



ware, porcelain or hard rubber, and assume a 

variety of forms, some of which are shown in Figs. 

310, 31 1 and 312. Of whatever material they are 

made, it is necessary that the 

surface on which the wire rests, 

or around which it is wrapped, 

should be smooth, so as to avoid 

abrasion, either of its insulat 

ing covering or of the wire i - 

self. 

Two things are to be con 
sidered in the selection of an 
insulator, viz : 

(1.) The insulating power of 
the material of which the in- 
sulator is composed, so as to Fig. 3 1 2. Hard 
reduce the leakage as much as Ru ^ r Insulator. 
possible. (See Leakage, Electric.} 

(2.) The tensile strength of the material, so 




that in case of heavy wires no breaks may result 
from the fracture of the insulator. 

Some forms of insulators are shown in Figs. 
310, 311 and 312. They are screwed to the pins; 
by the threads shown. The insulating materials 
of which they are formed are of glass, porcelain 
and hard rubber respectively. 

Insulator, Window-Tube A tube 

of vulcanite or other insulating material pro- 
vided for the insulation of a wire entering a 
room. 

The wire conductor passes through the middle 
of the tube, which is firmly fixed in an opening 
passing through the window frame. 

— A form of double- cup 



Insulator, Z — 

insulator in which the insulating material 
earthenware or porcelain, is made in a single 
piece, instead of in two separate pieces. 

The body of the insulator is conical in form,, 
and the interior air space presents a shape ap- 
proximately that of the letter Z. 

The double form is used in order to diminish 
the leakage. 

Intensity Armature. — (See Armature, 
Intensity.) 

Intensity, Connection of Voltaic Cells for 

■ — A term formerly employed for series- 
connected voltaic battery cells. (Obsolete.) 

Intensity, Magnetic — Density of 

magnetic induction. 

Magnetic flux per square centimetre. 

A committee of the American Institute of Elec- 
trical Engineers on "Units and Standards," pro- 
poses the following definition for magnetic inten- 
sity: 

The induction density at a point within an ele- 
ment of surface is the surface differential at that 
point. 

The practical unit of magnetic intensity U 
10 s or 100,000,000 C. G. S. lines per square cen- 
timetre. 

In practice, excluding the earth's field, intensi- 
ties range from 100 to 20,000 C. G. S. lines per 
square centimetre, and the working unit should,, 
perhaps, have the prefix milli or micro. 

Intensity, Magnetic, Pole of The 

earth's magnetic poles as determined by 
means of the oscillations of a magnetic- - 
need'e. 



Int.] 



293 



[Ion* 



The points of the earth's greatest magnetic 
intensity. 

Intensity of Current. — (See Current, In- 
tensity of.) 

Intensity of Field. — (See Field, Inten- 
sity of.) 

Intensity of Light.— (See Light, Inten- 
sity of.) 

Intensity of Magnetization.— (See Mag- 
netization, Intensity of.) 

Intensity, Photometric, Unit of — 

The amount of light produced by a candle 
that consumes two grains of snermaceti wax 
per minute. (See Candle.) 

Inter Air Space.— (See Space, Inter Air.) 

Intercrossing. — In a system of telephonic 
communication, a device for avoiding the dis- 
turbing effects of induction by alternately 
crossing equal sections of the line. (See 
Connection, Telephonic Cross.) 

Interference of Electro-Magnetic 
Waves. — (See Waves, Electro-Magnetic, 
Interference of.) 

Interlocking Apparatus.— (See Appa- 
ratus Interlocking?) 

Intermittent Contact. — (See Contact, In- 
termittent?) 

Intermittent Cross.— A form of electric 
cross. (See Cross, Electric?) 

Intermittent Current.— (See Current, In- 
termittent?) 

Intermittent Disconnection. — (See Dis- 
connection, Intermittent ) 

Intermittent Earth.— (See Earth, Inter- 
mittent?) 

Internal Circuit. — (See Circuit, In- 
ternal.) 

Internal Polarization of Moist Bodies.— 
(See Polarization, Internal, of Moist 
Bodies?) 

Interrupter, — Any device for interrupting 
or breaking a circuit. 

Interrupter, Automatic An auto- 
matic contact breaker, (See Make-and- 
Break. Automatic ?) 



Interrupter, Reed — A term some- 
times applied to a tuning-fork interrupter. 
(See Interrupter, Tuning-Fork.) 

Interrupter, Tuning-Fork An in- 
terrupter in which the successive makes and 
breaks are produced by the vibrations of a 
tuning-fork or reed. 

The tuning-fork or reed is maintained in vibra- 
tion by any suitable means. Such interrupters 
are applied to various uses. Synchronous mul- 
tiplex telegraphy affords an example of such uses. 

Invariable Calibration of Galvanometer. 

— (See Calibration, Invariable, of Galva- 
nometer?) 

Inverse Electromotive Force. — (See Force -, 
Electromotive, Inverse?) 

Inverse or Make-Induced Current. — (See 
Current, Make- Induced?) 

Inverse Secondary Current.— (See Cur- 
rent, Inverse Secondary?) 

Inversion, Thermo-Electric An 

inversion of the thermo-electric electromotive 
force of a couple at certain temperatures. 
(See Diagram, Thermo-Electric .) 

Invert Insulator. — (See Insulator, In- 
vert.) 

Inverted Induction Coil. — (See Coil, 
Induction, Inverted?) 

Inverted Type of Dynamo. — (See Dy- 
namo, Inverted.) 

Invisible Electric Floor Matting. — (See 
Matting, Invisible Electric Floor?) 

Ions. — Groups of atoms or radicals which 
result from the electrolytic decomposition of 
a molecule. 

The ions are respectively electro-positive and 
electro-negative. The electro-positive ion ap- 
pears at the plate connected with the electro- 
negative terminal, or at the kathode, and is called 
the kathion* 

The electro -negative ion appears at the plate 
connected with the electro-positive terminal, or 
at the anode t and is called the anion. (See 
Electrolysis, Kathion. Anion.) 

Ions, Electro-Negative The neg- 
ative atoms, or groups of atoms, called rad- 
icals, into which the molecules of an electro- 



Ion.J 



294 



[ISO. 



lyte are decomposed by electrolysis. (See 
Electrolysis.) 

The electro -negative ions are called the anions, 
because they appear at the anode of a decompo- 
sition cell. (See Anions. Anode.) 

Ions, Electro-Positive — The pos- 
itive atoms, or groups of atoms, called rad- 
icals, into which the molecules of an electro- 
lyte are decomposed by electrolysis. (See 
Electrolysis I) 

The electro-positive ions are called the kathions, 
because they appear at the kathode of a decom- 
position cell. (See Kathion. Kathode.) 

Iron-Clad Electro-Magnet. — (See Mag- 
net, Electro, Iron-Clad.) 

Iron-Clad Magnet.— (See Magnet, Iron- 
Clad^ 

Iron Core, Effect of, on the Magnetic 
Strength of a Hollow Coil of Wire 

An increase in the number of lines of mag- 
netic force, beyond those produced by the 
current itself, due to the opening out of the 
closed magnetic circuits in the atoms or 
molecules of the iron. 

The atoms or molecules of the iron possess 
naturally closed magnetic circuits, or closed lines 
of magnetic force, lying entirely within the mass 
of the iron. When the iron is placed in a magnetic 
field, these minute closed circuits open out and 
are added to the lines of force produced by the 
circuit itself. The opening out of these closed 
atomic or molecular lines of magnetic force is at- 
tended by the formation of lines of polarized 
molecules or atoms. 

Roughly speaking, according to Lodge, for 
each single line of magnetic force produced by the 
electric current, there are some 3,000 lines of 
magnetic force added to it from the iron, the ex- 
act number varying with the kind of iron, the 
physical condition of the iron and the degree of 
magnetization. 

Iron, Galvanized ■ — Iron covered by 

a layer of zinc by dipping it in a bath of 
molten zinc. 

The process of galvanizing iron is designed to 
prevent the corrosion or rusting of the iron on 
exposure to the air. (See Metals, Electrical Pro- 
tection of.) 

The word galvanized probably had its origin in 



an assumed galvanic or voltaic action, in causing 
the zinc to adhere to the iron. The true galvanic 
or voltaic action, viz., the galvanic protection, 
comes after the galvanizing process is completed. 

Iron-Work Fault of Dynamo. — (See 
Fault, Iron- Work, of Dynamo I) 

Irreversible Heat— (See Heat, Irreversi- 
ble^ 

Irritability, Electric Irritability 

of nervous or muscular tissue by an electric 
discharge. 

Irritability, Electric, Diminished 

A decreased irritability of nervous or muscu- 
lar tissue, produced by an electric current of 
given strength. 

Diminished electric irritability is often present 
in certain diseases of the motor apparatus. 

Irritability, Electric, Increased 

An irritability of nervous or muscular tissue 
produced by a much weaker electric current 
than that required to produce it in normal 
tissue. 

Irritability, Faradic —Muscular 

contractions produced by the action of a 
faradic current on a nerve. 

The action of the faradic current is to cause a 
prolonged tonic contraction, which continues 
while the current continues. Though the natural 
action is to produce a contraction, followed by a 
relaxation on each make and break, yet the makes 
and breaks follow one another so rapidly that the 
relaxation has not time to occur before the next 
contraction follows. 

Irritability, Galvanic —Muscular 

contractions produced by the action of a gal- 
vanic current. 

The action of a galvanic current is to cause a 
single, quick, momentary contraction of a muscle 
on each starting or completion of the circuit. 

The contractions are stronger in the case of 
galvanic currents when the direction of the cur- 
rent is reversed with a commutator instead of by 
an actual break at the poles. Such a break is 
called a voltaic alternative, and the currents so pro- 
duced voltaic alternatives. (Sea Alternatives, 
Voltaic.) 

Isobaric Lines. — (See Lines, Isobaric.) 

Isobars. — Lines connecting places on the 



Iso.] 



295 



[Jar 



earth's surface which have the same barome- 
tric pressure. 

The isobaric lines are generally corrected for 
differences of elevation of the surface. 

Isobars are often called isobaric lines. 

A study of the isobaric lines, or isobars, is of 
great assistance in making forecasts or predictions 
of coming changes in the weather. 

Isochasmen Curves. — (See Curves, Iso- 
chasmen.) 

Isochronism. — Equality of time of vibra- 
tion or motion. 

Isoehronize. — To produce equality of 
time of vibration or motion. — (See Isochron- 
ism?) 

Isochronizing. — Producing equality of 
time of vibration or motion. (See Isochron- 
z'sm.) 

Isochronous Titrations or Oscillations. 
— (See Vibrations or Oscillations, Isochron- 
otis.) 

Isoclinic Chart. — (See Chart, Inclina- 
tion?) 

Isoclinic Lines. — (See Lines, Isoclinic?) 

Isodynaniic Chart. — (See Chart, Isody- 
fiamic?) 



Isodynaniic Lines. — (See Lines, Isody- 
namic?) 

Isodynaniic Map. — (See Chart, Isody- 
7iamic.) 

Iso-Electric Points.— (See Points, Iso- 
electric.) 

Isogonal. — Pertaining to the isogonic lines. 
Isogonal Lines. — (See Lines, Isogonal.) 
Isogonal Map or Chart.— (See Map or 
Chart, Isogonal?) 
Isotonic. — Pertaining to the isogonal lines. 
Isotonic Chart. — (See Chart, Isogonic?) 
Isotonic Lines. — (See Lijies, Isogonic) 
Isotonic Map.— (See Map, Isogonic?) 

Isolated Electric Lighting 1 .— (See Light- 
ing, Electric, Isolated?) 

Isolatine. — A kind of insulating material. 

Isothermal Surfaces. — (See Surfaces, Iso- 
thermal.) 

Isotropic Conductor. — (See Conductor, 
Isotropic?) 

Isotropic Medium. — (See Medium, Iso- 
tropic.) 



J. — A contraction proposed for Joule. 
Jablochkoff Candle.— (See Candle, Jab- 
tochkoff.) 

Jacketed Magnet.— (See Magnet, Jack- 
eted?) 

Jacobi's Law. — (See Law, Jacob i's.) 

Jar, Electric —A name formerly 

given to the Leyden jar. 

Jar, Leyden A condenser in the 

form of a jar, in which the metallic coatings 
are placed opposite each other on the outside 
and the inside of the jar respectively. 

The metal coatings should not extend to more 
than two-thirds of the height of the jar, the rest 
of the glass being varnished to avoid the creeping 
of the charges over the glass in damp weather. 
The inside coating is connected by means of a 



metallic chain to a knob on the top of the jar, as 
shown in Fig. 313. The conductor supporting 
the knob passes through a dry cork or plug of 
some insulating material. 

To charge the jar, the outside coating is con- 
nected with the earth, as 
by holding it in the hand, 
and the outside coating 
is connected with the 
conductor of a machine. 
(See Condenser. Accu- 
mulator ) 

The inner coating of 
the jar is usually con- 
nected with the knobby 
means of a chain or wire *&-***• Uydm Jar. 
as shown above. This necessitates a support for 
the ball and stem, which is generally obtained by 
a cork or wooden plug inserted in the mouth of 




3ar.] 



296 



[Jek 



the jar. Such a form, however, is extremely ob- 
jectionable, since, although the top of the jar be 
covered with shellac varnish to avoil leakage, it 
affords but a poor insulation in damp weather, be- 
cause both the metallic rod supporting the ball and 





&*£• 3 J 4" S* r William Thomson's Ley den Jar. 
the damp wood or cork are in connection with the 
glass and thus facilitate leakage. 

To overcome these objections a form of jar has 
been devised by Sir William Thomson, in which the 
knob is supported on three feet, which rest on the 
inner coating. In this form the uncoated glass 
can be readily kept dry and clean. This form is 
shown in Fig. 314. 

A layer of sulphuric acid is sometimes employed 
for the inner coating of the Leyden jar. This 
serves the double purpose of acting as a coating 
and an absorber of moisture during damp 
weather. 

Jar, Leyden, Capacity of — The 

quantity of electricity a Leyden jar will hold 
at a given difference of potential. 

The capacity of a jar is equal to the quantity 
of electricity divided by the difference of potential 
such quantity produces in the jar; or the capacity 

= — , where Q = the quantity, and V, the differ- 
ence of potential. 

Jar, Leyden, Coatings of — (See 

Coatings of Leyden Jar.) 

Jar, Lightning A Leyden jar, the 

coatings of which consist of metallic filings. 

As the discharge passes, an irregular series of 
sparks appear, which somewhat resemble in their 
shape a lightning flash. Hence the origin of the 
term. 

Jar of Secondary Cell. — The containing 



vessel in which the plates of a single secondary 
cell are placed. 

Jar, Porous A porous cell. (See 

Cell, Porous^) 

Jar, Scintillating — A Leyden jar, 

the coatings of which, instead of being formed 
of continuous sheets of tin-foil or other con- 
ducting substances, are formed of small pieces 
of such substances, placed at regular intervals 
on the glass or dielectric so as to leave a small 
space between them. 

Such a jar has received the name of scintillat- 
ing jar, because when discharged by connecting 
its two opposite coatings the discharge appears as 
minute eparks, whLh jump across the space 
between the metallic pieces. 

Jar, Unit A small Leyden jar some- 
times employed to measure approximately the 
quantity of electricity passed into a Leyden 
battery or condenser. 

As sh 'Wn in Fig. 315, the unit jar consists of a 
small Leyden jar j, whose outer coating is con- 
nected with a sliding metallic 
rod b, provided at each end 
with a rounded knob, and the 
inner coating of which is con- 
nected with a metallic knob c, 
placed as shown, inside a 
glass jar d, opposite a ball on 
the lower end of b. 

When, now, the inside of 
the unit jar, or the end con- 
nected with c, is connected 
with the charging source, such 
as a machine, and the outside 
at a, is connected with the jar 
or jars to be charged, for 
every spark that passes be- 
tween d and c, a definite quantity has passed a. 

The value of this unit charge may be varied by 
varying the distance between d and c. 

The smaller the unit jar is in proportion to the 
jar to be charged, and the shorter the distance 
between c and d, the more reliable are the com- 
parative results obtained. 

Jars, Leyden, Charging, by Cascade 

— (See Cascade, Charging Leyden Jars by.) 
Jet, Gas, Carcel Standard — A 

lighted gas jet employed for determining the 
candle-power of gas by measuring the height 




Fig>3T5 



Jet. 



297 



[Joi. 



•of a jet of gas burning under a given press- 
ure, and used in connection with the light of 
a larger gas burner, burning under similar 
conditions, for the photometric measurement 
of electric lights. 




Fig, 316. Seven-Carcel 
Standard Gas Jet. 



Fig-, 317. Carcel Candle 
Burner. 



In Fig. 316 is shown a section of a seven-carcel 
standard gas jet, and in Fig. 317, a section of a 
candle burner, connected within the same service 
pipe. The gas for both burners is received in a 
chamber, from whence it passes by an opening to 
the burner, under the constant pressure obtained 
by the weight of the bell C, ar.d the tube A. The 
burner shown in Fig. 317, which is used as the 
standard of comparison, will give a candle-power 
determined from the height of the jet of the 
burning gas. This height is measured in milli- 
metres by the motion of a circular screen. 

The determination of the candle-power of gas by 
means of a jet photometer is only approximately 
correct, unless many precautions are taken. 

Jet Photometer. — (See Photometer, Jet) 
Jewelry, Electric Minute incan- 
descent electric lamps substituted for the 
rarer gems in articles of jewelry. 

The lamps are lighted by means of small pri- 
mary or storage batteries, carried in the pocket or 
elsewhere on the person. 

Joint, American Twist A tele- 
graphic or telephonic joint in which each of 
the two wires is twisted around the other. 
(See Joint, Telegraphic or Telephonic) 



The twisted joint is sometimes subsequently 
soldered. 



Fig 318. American Twist Joint. 

The American twist joint is shown in Fig. 318. 
This joint is easLy made and is very serviceable. 

Joint, Bell-Hanger's A joint for 

telegraphic or telephonic wires in which the 
ends are merely looped together. (See Joitit, 
Telegraphic or Telephonic) 

Joint, Britannia A telegraphic or 

telephonic joint in which the wires are laid 
side by side, bound together and subsequently 
soldered. (See Joint, Telegraphic or Tele- 
phonic) 




Fig,3iq. Britannia Joint. 

The Britannia joint is shown in Fig. 319. No, 
16 wire, B. W. G., is used as the binding wire. 

Joint, Butt An end-to-end joint. 

A joint effected in wires by placing the 
wires end on and subsequently soldering. 

Butt joints are formed by bringing the ends to 
be joined together and securing them while in 
such position. 

Joint, Butt and Lap, of Belts — The 

joint in a leather belt, employed for transmit- 
ting power from a line of shafting where the 
ends are simply brought together and laced, 
is called a butt joint, in contradistinction to a 
lap joint, or a joint formed by placing one end 
of the belt over the other and lacing or rivet- 
ing the two. 

In using delicate galvanometers, the slightest 
change in the speed of the engine driving the 
dynamo-electric machine producing the current, 
causes an annoying fluctuation of the needle that 
prevents accurate reading, when lap joints are used 
in the b Jt instead of butt joints, unless the former 
are very carefully made. Lap joints may also cause 
a flickering in the lights. When, however, lap 
joints are made by cutting the belt by an oblique 
section and properly securing them so that their 



Joi.] 



298 



[Jou 



elevation at the joint is no greater than elsewhere, 
the lap joint is preferable to the butt joint. 

Joint, Expansion A joint for under- 
ground conductors, tubes or pipes, exposed 
to considerable changes of temperature, in 
which a sliding joint is provided to safely 
permit a change of length on expansion or 
contraction. 

Joint, Insulation A joint in an insu- 
lating material or covering in which a conti- 
nuity is insured in the conducting as well as 
the insulating substance. 

Joint, Lap A joint effected by over- 
lapping short portions near the ends of the 
things to be joined, and securing them while 
in such position. 

Joint, Lap, for Wires A joint 

effected between two wires by overlapping 
their ends and subsequently soldering. 

Joint, Magnetic The line of junc- 
tion between two separate parts of magnetiza- 
ble materal. 

Magnetic joints should be of such a nature as 
to permit the passage of the lines of magnetic 
force with the least increase in the resistance of 
the magnetic circuit. 

Magnetic joints in the field magnets of a dynamo- 
electric machine should be as few as possible, since 
the resistance of the best magnetic joint to the 
passage of the lines of force is necessarily greater 
than that of the same material without such 
joints. 

Joint, Metallic Conducting A joint 

in a conductor in which a continuity of con- 
ducting power is secured. 

Joint Resistance of Parallel Circuits. — 

(See Resistance, Joint, of Parallel Circuits?) 

Joint, Sleeve ■ — A junction of the 

ends of conducting wires obtained by passing 
them through tubes and then twisting and 
soldering. 

All joints should be soldered, but in so doing 
care must be taken that the soldering liquid or 
solid employed is free from acids or other corro- 
sive materials, and that all traces of the soldering 
liquid or solid are removed from the wire before 
the joint is covered with insulating material. 
Kerite, okonite or other insulating tape, should 



preferably be wrapped around the joint after 
it is soldered. 

In making a joint in a gutta-percha covered 
wire, such as a submarine cable, the following 
method may be employed: The bared and 
cleansed wires are twisted together and soldered. 
The soldered joint is then covered with a layer 
of plastic insulating material made of a mixture 
of gutta-percha, tar and rosin. (See Ckattertori 's 
Compound.) In order to insure a good junction 
between this and the gutta-percha covering on the 
rest of the wire, the outer surface of the gutta- 
percha is removed for about two inches from each 
side of the joint, so as to remove its oxidized sur- 
face. After the coating is put on, it is warmed 
gently by a warm joining tool, not by the flame 
of a lamp. A sheet of warmed gutta-percha is 
then wrapped around the joint, and while it and 
the joint are still hot, another coating of the 
plastic insulating material, is applied. Successive 
layers of gutta-percha and some other insulating 
material are generally applied in the case of sub- 
marine cables. — ( Culley.) 

Joint, Telegraphic, Mclntire's Parallel 

Sleeve A joint for telegraphic or other 

wires, in which the ends to be joined are 
slipped into parallel sleeves or tubes, which 
are afterward twisted around each other. 

A general view of the parallel sleeve joint, both 
before and after twisting, is shown in Fig. 320. 



C 



Fig. 320. Mclntire's Parallel Sleeve Joint. 

The twisting is done by means of the specially 
devised twisting clamp shown in Fig. 321. 




Fig. 321. Twisting Cla7npfor Mclntire's Parallel Joint, 

Joint, Telegraphic or Telephonic 



A juncture of the ends of two electric con- 
ductors so as to insure a permanent junc- 
tion whose resistance shall not be appreci- 
ably greater per unit of length than that of 
the rest of the wire. 



Joi.] 

In making a joint, care should always be taken 
to scrape the insulating material from the wires 
and clean their surfaces before twisting them to- 
gether. 

Telegraph wires were formerly joined by the 
ordinary bell-hangers' joint; that is, the wires were 
simply looped together. The constant vibrations 
to which the wires are subjected caused such a 
joint to be abandoned and an improvement intro- 
duced by bolting the ends together, as shown in 
Fig. 322. 



Fig- 322. Telegraphic Joint. 



Joint, Testing of 



-Ascertaining the 



resistance of the insulating material around 
a joint in a cable. 

The resistance of the insulating material of a 
cable at a joint is necessarily high, since the 
joint forms but a small part of length of the cable. 
It should not, however, be large as compared with 
an equal length of another part of the cable with 
a perfect core. 

Two methods for testing cable joints are gener- 
ally employed, viz. : 

(1.) A conductor is charged through the joints 
for a given time, and the deflection obtained by 
its discharge compared with the discharge of the 
same condenser charged for an equal length of 
time through a few feet of perfect cable. 

(2.) A charged conductor is permitted to dis- 
charge itself through the joint, and the amount 
lost in a given time noted. 

For description of different methods, see 
Kempe's " Handbook of Electrical Testing." 

Joulad. — A term proposed for the Joule. 



299 [Kao. 

This term is not generally adopted. (See 
Joule.) 

Joule. — The unit of electric energy or 
work. 

The volt-coulomb. 

The amount of electric work required to 
raise the potential of one coulomb of elec- 
tricity one volt. 

The joule may be regarded as a unit of energy 
or work in general, apart from electrical work or 
energy. 

1 joule = 10,000,000 ergs. 

1 joule = . 73732 foot-pounds. 

1 joule = 1 volt-coulomb. 

I joule = .24 calorie. 

4.2 joules = 1 small calorie. 

1 joule per second = 1 watt. 

The British Association proposed to call one 
joule the work done by one watt in one second. 

Joule, as a Heat Unit. — The quantity of 
heat developed by the passage of a current 
of one ampere through a resistance of one 
ohm. (See Joule.) 

Joule Effect.— (See Effect, Joule?) 

Joule's Cylindrical Electro-Magnet. — 

(See Magnet, Electro, Joule s Cylindrical?) 

Joule's Law. — (See Laws oj Joule?) 
Junction Box. — (See Box, Junction) 
Jump-Spark Burner. — (See Burner ; 

Jtmp-Spark.) 
Junction, Thermo-Electric. — A junction 

between any thermo-electric couple. (See 

Cell, Thermo-Electric?) 



K. — A contraction for electrostatic capa- 
city. (See Capacity, Electrostatic?) 

K. C. C. — In electro-therapeutics, a brief 
method of writing kathodic closure contrac- 
tion, or the effects of muscular contraction 
observed at the kathode on the closure of a 
circuit. 

K. I). C. — In electro-therapeutics, a brief 
method of writing kathodic duration con- 



traction, or the effects of muscular contrac- 
tion observed at the kathode after the current 
has been passing for some time. 

K. "W. — A contraction for kilo-watt. (See 
Watt, Kilo?) 

Kaolin. — A variety of white clay some- 
times employed for insulating purposes. 

Jablochkoff sometimes employed kaolin be- 
tween the parallel carbons of his electric candle 



300 



[Key. 



for the purpose of insulating them from each 
other. He also devised an electric lamp in which 
a spark of considerable difference of potential, 
obtained from an ordinary induction coil, was 
caused to raise a surface of kaolin to incan- 
descence by passage over it. 

Kapp Lines. — (See Lines, Kapp?) 

Kartayert. — A kind of insulating material. 

Katelectrotonns. — A word sometimes used 
instead of kathelectrotonus. (See Kathe- 
lectrotonus?) 

Kathelectrotonic State. — (See State, 
Kathelectrotonic?) 

Kathelectrotonic Zone. — (See Zone, 
Kathelectrotonic?) 

Kathelectrotonus. — In electro-therapeu- 
tics, the condition of increased functional ac- 
tivity that occurs in a nerve in the neighbor- 
hood of the kathode or negative electrode. 
(See Electrotonus.) 

Kathion. — The electro-positive ion, atom 
or radical into which the molecule of an 
electrolyte is decomposed by electrolysis. 
(See Electrolysis. Ions.) 

Kathion is sometimes written cathion. 

In electrolysis the kathion, or the electro-posi- 
tive ion or radical, appears at the kathode or 
electro-negative electrode. Similarly, the anion, 
or the electro-negative ion or radical, appears at 
the anode or the electro-positive electrode. 

Kathodal. — Pertaining to the kathode. 
(See Kathode?) 

Kathode. — The conductor or plate of an 
electro-decomposition cell connected with the 
negative terminal or electrode of a battery or 
other source. 

The word kathode is sometimes applied to the 
negative terminal of a battery or source, whether 
connected with a decomposition cell or not. It 
is preferable, however, to restrict its use to de- 
composition cells. (See Anode.) 

The word kathode is sometimes written cathode. 

Kathodic. — Pertaining to the kathode. 
(See Kathode.) 

Kathodic Electro-Diagnostic Reactions. 

— (See Reactions, Electro-Diagnostic?) 

Keeper of Magnet. — (See Magnet, Keeper 
of.) 



Kerite. — An insulating material. 
Kerr Effect— (See Effect, Kerr?) 
Key Board. — (See Board, Key.) 

Key, Capillary Contact A form of 

fluid contact in which the circuit is closed or 
broken by means of a wire which is dipped 
into or removed from the surface of a mass 
of mercury. 

In order to avoid an increase in the resistance 
of the circuit, due to the formation of oxide of 
mercury, the contact surface of the mercury is 
kept covered with a layer of dilute alcohol. 

Key, Discharge A key employed to 

enable the discharge from a condenser or 
cable to be readily passed through a galva- 
nometer for purposes of measurement. 

Key, Discharge, Kenipe's A dis- 
charge key constructed as shown in Fig. 323. 




Fig. 323. Kempe's Discharge Key. 

The solid lever, hinged at one extremity, plays 
between two contacts connected to two terminals, 
and has two finger triggers at its free end marked 
"Discharge" and "Insulate," connected respec- 
tively to two ebonite hooks. The hook attached 
to that marked ' ' Discharge " is a little higher than 
the other, so that when the lever is caught against 
it, the key rests in an intermediate position be- 
tween the contacts, and, when caught against the 
lower trigger, it rests against the bottom contact. 
When in the last position, a depression of the 
" Insulate " trigger causes the lever to spring up 
against the second hook, thus insulating it from 
either contact, and on the depression of the " Dis- 
charge ' ; trigger, the lever springs up against the 
top contact. 

Key, Discharge, Webb's A dis- 
charge key constructed as shown in Fig. 324. 

A horizontal lever L, Fig. 324, passing between 
two contacts and hinged at J, is pressed upward 
by a spring. The free end of this lever termi- 
nates in two steps, I and 2. A vertical lever, pro- 



Key.] 



301 



[Key. 



videdwith an insulating handle, is jointed at J', 
and has at C, a projecting metallic tongue that 
engages in the upper step when the lever H, is 
vertical, and on the lower step when it is slightly 
moved from the free end. 

When the projection C, rests on the lower step 
2, the lever L, is intermediate between the top 
and bottom contacts, and is, therefore, discon- 




Fig. 324. Webb's Discharge Key. 

nected from either of them; but, when it rests on 
the upper step, it is in contact with the lower 
contact. 

When the lever H, is so moved as to have the 
projection C, away from both steps, the lever L, 
is pressed by its spring against the upper contact. 

The battery terminals are connected with the 
condenser terminals when the lever L, is touching 
the lower contact, but when the lever L, touches 
the top contact, the condenser is connected with 
the galvanometer terminals. 

Key, Double-Contact Form of Bridge, 
Sprague's A key designed to succes- 
sively close two separate circuits. 




3 4 

Spr ague's Double-Contact Key. 

Sprague's double-contact key is shown in Fig. 
325. On depressing K, the contacts c, c, are first 
closed and afterwards contacts at c' , c' . Metallic 



pieces, 1, 2, 3 and 4, serve to make contacts with 
apparatus used in connection with the key. 

The battery circuit is connected to I and 2, 
and the galvanometer to 3 and 4, so that the bat- 
tery circuit is closed first, and the galvanometer 
afterwards. This form of key is used in connec- 
tion with the Wheatstone Bridge. 

Key, Double-Contact, Lambert's 

A key used in cable-work, and constructed 
as shown in Fig. 326. 




Fig 326. Lambert's Double- Contact Key. 

In Thomson's method for the determination of 
electrostatic capacity, the capacity of the cable 
is compared with that of a condenser containing 
a known charge. These two charges are so con- 
nected electrically as to discharge into and 
neutralize each other if equal, but if not, to pro- 
duce a galvanometer deflection by a charge 
equal to their difference. 

A Lambert double contact key is shown in Fig. 
326. The connections are such that the pushing 
forward of K, depresses keys that permit a bat- 
tery to simultaneously charge the condenser and 
the cable. On drawing K, back, the two charges 
are allowed to mix. Then on depressing K, the 
difference of the charges, if any, is discharged 
through the galvanometer. 

Key, Double-Tapper The key used 

in a system of needle telegraphy to send 
electric impulses through the lines in alter- 
nately opposite directions. (See Telegraphy, 
Single-Needled) 

Key, Increment —A telegraphic key 

so connected that an increase or increment 
in the line current occurs whenever the key is 
depressed. 

The increment key is used in duplex and quad- 
ruplex systems of telegraphic transmission. 

Key, Increment, of Quadruples Tele- 
graphic System A key employed to 

increase the strength of the current and so 
operate one of the distant instruments in a 



Key.] 



302 



[Key. 



quadruplex system by an increase in the 
strength of the current. (See Telegraphy, 
Quadruplex^) 

Key, Magneto-Electric A tele- 
graph key for sending an electric impulse 
into a line, so arranged that a coil of wire on 
an armature connected with the key lever is, 
by the movements of the key, moved toward 
or from the poles of a permanent magnet, the 
movements of the key thus producing the 
currents sent into the line. 

Key, Plug A simple torm of key in 

which a connection is readily made or broken 
by the insertion of a plug of metal between 
two metallic plates that are thus introduced 
into a circuit. 

A form of plug key is shown in Fig. 327. 




Fig. 327. Plug Key. 

Key, Reversing 1 A key inserted in 

the circuit of a galvanometer for obtaining 
deflections of the needle on either side of the 
galvanometer scale. 

A form of reversing key is shown in Fig. 328. 
The galvanometer terminals are connected to the 
binding posts 2 and 3, and the circuit terminals 
to the other two posts. On depressing K, the 




Fig- 328. Reversing Key. 

current flows m one direction and on depressing 
K', it flows in the opposite direction. Clamps, 
operated by handles, are provided so as to close 
either of the keys permanently, if so desired. 



Key, ReYersing, of Quadruplex Tele- 
graphic System A key employed to 

reverse the direction of the current and so 
operate one of the distant instruments, in a 
quadruplex system, by a change in the 
direction of the current. (See Telegraphy, 
Quadruplex^) 

Key, Short-Circuit A key which 

in its normal condition short circuits the gal- 
vanometer. 

JV 




Fig- 32Q. Short- Circuit Key. 

Such a short-circuit key is provided for the 
purpose of protecting the galvanometer from in- 
jury by large currents being accidentally passed 
through its coils. In the form shown in Fig. 329, 
the spring S, rests against a platinum contact ;. 
but when depressed by the insulated head at K, 
it rests against an ebonite contact, and throws 
the galvanometer into the desired circuit. 

The key is provided with double binding posts 
at P and N, for convenience of attachment to re- 
sistance coils, batteries, etc. 

In the form of a short-circuit key shown in Fig. 
330, a catch is provided for the purpose of keep- 
ing the key down when once depressed. Its 
arrangement will be readily understood from an 
inspection of the figure. 




Fig. 33o. Short- Circuit Key. 

Key, Sliding-Contact The key em- 

ployed in the slide form of Wheatstone 
bridge, to make contact with the wire over 
which the sliding contact passes. (See 
Bridge, Electric, Slide Form of.) 



Key.] 



303 



[Kit. 



Key, Stationary Floor 



— An electric 
key or push button placed on the floor so as 
to be readily closed by the foot. 

This form of key is especially suitable for use 
in connection with an electric bell and annuncia- 
tor for readily calling an attendant. (See Annun- 
ciator ; Electro-Magnetic.} 

Key, Telegraphic The key em- 
ployed for sending over the line the successive 
makes and breaks that produce the dots and 
dashes of the Morse alphabet, or the deflec- 
tions of the needle of the needle telegraph. 
(See Telegraphy, American System of.) 

Kick. — A recoil. 

Kicking Coil. — (See Coil, Kicking.) 

Kilo (as a prefix). — One thousand times. 

Kiloampere. — One thousand amperes. 

Kiloampere Balance. — (See Balance, 
Kiloampere) 

Kilodyne. — One thousand dynes. (See 
Dyne) 

Kilogramme. — One thousand grammes, 
or 2.2046 pounds avoirdupois. (See Weights, 
French System of) 

Kilojoule.— One thousand joules. 

Kilometre. — One thousand metres. 

Kilowatt. — One thousand watts. 

Kilowatt Hour. — (See Hour, Kilowatt) 

Kine. — A unit of velocity proposed by the 
British Association. 

A kine equals 1 centimetre per second. 

Kinetic Energy. — (See Energy, Kinetic) 

Kinetic Theory of Matter.— (See Matter, 
Kinetic Theory of) 

Kinetics, Electro A term some- 
times applied to the phenomena of electric 
currents, or electricity in motion, as distin- 
guished from electrostatics, or the phenom- 
ena of electric charges, or electricity at rest. 

Kinetograph. — A device for the simultane- 
ous reproduction of a distant stage and its 
actors under circumstances such that the 
actors can be heard at any distance from the 
theatre. 

The sounds heard by the distant audience are 
actual reproductions of those uttered during the 



performance, though not at the time of then- 
utterance. The appearance of the stage and its 
actors represents the appearance of a previous 
reproduction of the play or opera or other per- 
formance, as taken by means of a Kodak camera 
with a film cylinder and drop shutter, operated 
by an electric motor, exposing, say, forty plates 
a second. By means of a projecting lantern these 
photographic pictures are thrown on a curtain on 
a stage at the distant theatre in regular order of 
sequence, while a loud- speaking phonograph 
puts song and speech into the mouths of the 
mimic actors and thus gives the phantom stage 
the semblance of life and reality. 



Kite, Franklin's 



-A kite raised in 



Philadelphia, Pa., in June, 1752, by means of 
which Franklin experimentally demonstrated 
the identity between lightning and electricity, 
and which, therefore, led to the invention of 
the lightning rod. 

It is true that Dalibard, on the 10th of May, 
1752, prior to Franklin's experiment, succeeded 
in drawing sparks from a tall iron pole he had 
erected in France. This experiment was, how- 
ever, tried at the suggestion of Franklin, to whom 
it must properly be ascribed. 

A description of this kite is given by Franklin 
in the following letter: 

Letter XI, from Benj. Franklin, Esq., of Phil- 
adelphia, to Peter Collinson, Esq., 
F. R. S., London. 

"Oct. 19, 1752. 

"As frequent mention is made in public papers, 
from Europe, of the success of the Philadelphia 
experiment for drawing the electric fire from 
clouds by means of pointed rods of iron erected 
on high buildings, etc., it may be agreeable to 
the curious to be informed that the same experi- 
ment has succeeded in Philadelphia, though 
made in a different and more easy manner, which 
is as follows: 

' ' Make a small cross of two light strips of cedar, 
the arms so long as to reach to the four corners of a 
large thin handkerchief when extended; tie the 
corners of the handkerchief to the extremities of 
the cross, so you have the body of a kite, which, 
being properly accommodated with a tail, loop 
and string, will rise in the air like those made of 
paper, but this, being of silk, is fitter to bear the 
wet and wind of a thunder gust without tearing. 
To the top of the upright stick of the cross is to 



KniJ 



30± 



[Lag. 



be fixed a very sharp pointed wire rising a foot 
or more above the wood. To the end of the 
twine, next the hand, is to be tied a silk ribbon, 
and where the silk and twine join, a key may be 
fastened. This kite is to be raised when a thun- 
der gust appears to be coming on, and the per- 
son who holds the string must stand whhin a 
door or window, or under some cover, so that 
the silk ribbon may not be wet, and care must be 
taken that the twine does not touch the frame of 
the door or window. As soon as any of the 
thunder clouds come over the kite the pointed 
wire will draw the electric fire from them, and 
the kite, with all the twine, will be electrified, 
and the loose filaments of the twine will stand 
out every way, and be attracted by an approach- 
ing finger. And when the rain has wet the kite 
and twine so that it can conduct the electric fire 
freely, you will find it stream out plentifully from 
the key on the approach of your knuckle. At 
this key the phial may be charged, and from 
electric fire thus obtained spirits may be kindled, 
and all the other electric experiments be per- 
formed, which are usually done by the help of a 



rubbed glass globe or tube, and thereby the 
sameness of the electric matter with that of light- 
ning completely demonstrated. 

"B. Franklin." 

Knife Break Switch.— (See Switch, Knife 
Breaks 

Knot or Nautical Mile. — A length equal 
to 6,087 feet. 

The English statute mile is equal to 5,280 feet. 
The value of the nautical mile is therefore in excess 
of that of the statute mile. 

Kohlrauscli's Law. — (See Law of Kohl- 

rausch.) 

Krizik's Bars. — (See Bars, Krizi&'s.) 
Kyanized. — Subjected to the kyanizing 

process. (See Kyanizing.) 

Kyanizing". — A process employed for the 
preservation of wooden telegraphic poles by 
injecting a solution of corrosive sublimate 
into the pores of the wood. (See Pole, Tele- 
graphic?) 



L. — A contraction for co-efficient of in- 
ductance. (See Inductance, Co-efficient of.) 

L. — A contraction for length. 

Labile Galvanization. — (See Galvaniza- 
tion, Labile?) 

Lag*, Angle of The angle through 

which the axis of magnetism of the armature 
of a dynamo-electric machine is shifted by 
reason of the resistance its core offers to sud- 
den reversals of magnetization. 

An armature of a bi polar dynamo- electric ma- 
chine has its magnetism reversed twice in every 
rotation. The iron of the core resists these mag- 
netic reversals. The result of this resistance is to 
shift the axis of magnetism in the direction of ro- 
tation. The angle through which the axis has 
thereby been shifted is called the angle of lag. 

The term, angle of lag, is sometimes incorrectly 
applied so as to include a similar result produced 
by the magnetization due to the armature current 
itself. It is this latter action which, in armatures 
"with soft iron cores, is the main cause of the angle 



of lead. (See Brushes, Lead of. Lead % Angle 
of.) 

Lag-, Angle of, of Current An 

angle whose tangent is equal to the ratio of 
the inductive to the ohmic resistance. 

An angle, the tangent of which is equal to 
the inductive resistance of the circuit, divided 
by the ohmic resistance of the circuit. 

An angle, the co-sine of which is equal to 
the ohmic resistance of the circuit, divided 
by the impedance of the circuit. 

Lag, Magnetic A magnetic viscos- 
ity as manifested by the sluggishness with 
which a magnetizing force produces its mag- 
netizing effects in iron. 

The tendency of the iron core of a magnet, 
or of the armature of a dynamo-electric ma- 
chine, to resist, and, therefore, retard mag- 
netization. 

This retardation, or lag, is called the magnetic 
lag. 

The lead necessary to give the brushes of a dy- 
namo-electric machine to insure quiet action has by 



Lain.] 



305 



[Lam. 



some been erroneously ascribed to the magnetic 
lag. The lead, though due to lag in part, in reality 
is mainly due to the resultant magnetization of 
the armature both by the field magnets and by its 
own current. (See Lead, Angle of.) This dis- 
placement of the brushes is measured by an angle 
sometimes, though erroneously, called the angle 
of lag. (See Lag, Angle of '.) 

Lamellar Distri- 
bution of Magnet- 
ism. — (See Magnet- 
ism, Lamellar Dis- 
tribntion of.) 

Laminated Core. 
— (See Core, Lami- 
nated^) 

Laminating Core. 
— (See Core, Lami- 
nation of.) 

Lamination of 
Armature Core. — 
(See Core, Armature, 
Lamination of.) 

Lamination of 
Cores. — (See Core, 
Lamination of.) 

Lamp, All-Night 

A term some- 
times applied to a 
double - carbon arc 
lamp. (See Lamp, 
Electric Arc, Double** 
Carbon) 

A form of all-night 
arc lamp is shown in 
Fig. 331- When the 
consumption of the first 
pair of carbons has Fig. 331. All-Night Arc 
reached a certain limit Lamp. 

the current is automatically switched over to the 
other pair. 

Lamp, All-Night Electric — A lamp 

provided with carbon electrodes so as to burn 
all night without recarboning. 

A double-carbon electric lamp. (See 
Lamp, All-Night) 

Lamp, Arc An electric lamp, the 

source of whose lifjht is a voltaic arc. 




Lamp, Arc, Electric — An electric 

lamp in which the light is produced by a vol- 
taic arc formed between two or more carbon 
electrodes. 

The carbon electrodes are placed in various 
positions, either parallel, horizontal, inclined 
to one another or vertically one above the other. 
The latter is the form most generally adopted, 
since it permits the ready feeding of the upper 
carbon. 

The carbons are maintained during their con- 
sumption at a constant distance apart, by the aid 
of various feeding devices. Such devices are op- 
erated generally by trains of wheel- work, by me- 
chanical or electrical motors, or by the simple 
action of a spring, by gravity or by the attraction 
of a solenoid. 

The carbon pencils or electrodes are held in 
carbon holders, consisting of clutches or clamps, 
attached to the end of the lamp rods. 

When the lamp is not in operation the carbons 
are usually in contact with one another ; but, on 
the passage of the current, they are separated 
the require! distance by the action 
of an electro-magnet whose coi's 
are traversed by the direct or main 
current. 

In order to maintain the elec- 
trodes a constant distance apart, 
the upper carbon in some lamps is 
held in position by the operation of 
a clutch, or, in others, by a detent, 
that engages in a toothed wheel. 
The position of this clutch or de- 
tent is controlled by the action of 
an electro-magnet whose coils are 
usually situated in a shunt or de- 
rived circuit, of high resistance, 
around the electrodes. When the 
carbons are at their normal dis- 
tance apart, the shunt current is 
not of sufficient strength to move 
the clutch or detent from the position in which 
it prevents the downward motion of the upper 
carbon rod. When, however, by the burning 
or consumption of the carbons, the resistance 
of the arc has increased to an extent which can 
be predetermined, the increased current that is 
thereby passed through the shunt circuit is now 
sufficiently strong to release the clutch or de- 
tent, thus permitting the fall or feed of the upper 
carbon. In a well designed lamp this occurs 




Fig. 332. 
Arc Lamp. 



lam.] 



306 



[Lam. 



so gradually as to produce no perceptible effect 
on the steadiness of the light. 

Arc lamps are generally placed in series circuits, 
that is, in circuits in which the current passes suc- 
cessively through all the lamps in the circuit, and 
returns to the source. In order to avoid the break- 
ing of the entire circuit through the extinguish- 
ing of a single arc, on the breaking of its cir- 
cuit, an automatic safety device is provided for 
each lamp. This safety device consists essentially 
of an electro-magnet so placed in a shunt circuit, 
that, as the resistance of the arc becomes too 
great, the increased current, which will then flow 
through the coils of the electro-magnet, at last 
produces a movement of its armature which closes 
a short circuit around the lamp, and thus cuts it 
out of the circuit. 

Arc lamps assume a great variety of forms. A 
well known form is shown in Fig. 332. 

Lamp, Arc, Triple Carbon An arc 

lamp in which three carbon electrodes are 
used. 

The positive carbons consist of two ordinary 
cylindrical carbons, placed parallel to each other. 
The negative carbon is shaped like the figure 8. 
The arc is established between one of the positive 
carbons and the corresponding side of the nega- 
tive carbon. The feeding of the lamp is attended 
by a shifting back and forth of the arc between 
the positive carbons and from side to side of the 
negative carbons. 

The design of the triple carbon arc lamp is to 
produce a lamp of long life. 

Lamp Bracket, Electric 

— (See Bracket, Lamp, 

Electric?) 

Lamp Bulb. — (See Bulb, 
Lamp?) 

Lamp, Carcel — An 

oil lamp employed in France 
as a photometric standard. 

Fig. 333 shows a form of car- 
cel lamp. Like the standard 
candle, the carcel is a standard 
only when it consumes a given 
weight of the light-producing 
substance in a given time. 

Lamp, Chamber of 




The glass bulb or chamber of 
an incandescing electric lamp 
in which the incandescing conductor is 



Fig. 333- 
Carcel Lamp. 



placed, and in which is maintained a high 
vacuum. 

The transparency of the lamp chamber and 
consequently the efficiency of the lamp may de- 
crease — - 

( I . ) From the settling of dust or dirt on its outer 
walls. 

(2.) From the deposit of carbon or metal on its 
inner walls. 

To obviate the first cause of diminished trans- 
parency the outside of the lamp chamber should 
be frequently cleansed. The diminished trans- 
parency, due to the second cause, cannot be 
removed. When it has reached a certain point, it 
is more economical to replace the old lamp by a 
new lamp. 

In a properly made lamp the dimming of the 
lamp chamber is not apt to occur unless a stronger 
current than the normal current is passed through 
the lamp. 

Lamp Clamp. — (See Clamp for Arc 
Lamps?) 

Lamp, Contact A form of semi- 
incandescent electric lamp in which a carbon 
pencil is pressed against a slab of carbon or 
other refractory material. 

The source of light in an electric contact lamp 
is twofold, viz.: 

(1.) A minute arc formed at the points of im- 
perfect contact. 

(2.) The incandescence of the carbon pencil, 
and the points of the slab of carbon against which 
it is pressed. 

Lamp Contacts. — (See Contacts, Lamp?) 

Lamp, Electric, Arc, Carbon Elec- 
trodes for ■ — (See Electrodes, Carbon, 

for Arc Lamps?) 

Lamp, Electric, Arc, Differential ■ 

An arc lamp in which the movements of 
the carbons are controlled by the differential 
action of two magnets opposed to each other, 
one of whose coils is in the direct and the 
other in a shunt circuit around the carbons. 

Sometimes the differential coils are placed on 
the same magnet core. 

Lamp, Electric, Arc, Double Carbon 

— An electric arc lamp provided with two 
pairs of carbon electrodes, so arranged that 
when one pair is consumed, the circuit is auto- 
matically completed through the other pair. 



Xam.J 



307 



[Lam. 



Lamp, Electric Glow 



— A term em- 
ployed mainly in Europe for an incandescent 
electric lamp. (See Lamp, Electric, Inca?i- 
descent.) 

Lamp, Electric, Incandescent An 

electric lamp in which the light is produced 
by the electric incandescence of a strip or 
filament of some refractory substance, gener- 
ally carbon. 

The carbon strip or filament is usually bent into 
the form of a horseshoe or loop, and placed inside 
a glass vessel called the lamp chamber. The 
lamp chamber is exhausted by means of a mercury 
pump, generally to a fairly high vacuum. 

In order to insure the complete removal from 
the lamp chamber of all the air it originally con- 
tained, the carbon strips that are placed within it 
are maintained at a high temperature during the 
process of exhaustion. This temperature, in 
practice, is obtained by sending the current 
through the carbon strip as soon as nearly all 
the air is removed. Towards the end of the 
pumping operation the current is increased so 
as to raise the carbons to their full bril- 
liancy. 

The lamp chamber is also maintained at a 
ia'rly high temperature. 

To insure this heating of the walls of the lamp 
chamber by the incandescent carbons during 
pumping, for the purpose of driving off all the 
air adhering to the walls of the chamber, they are 
sometimes covered with some readily removable 
preparation of lamp black. 

The operation of driving off the gases absorbed 
by the carbons is termed the occluded gas process, 
and is essential to the successful sealing of an 
incandescent lamp. By its means, a considerable 
quantity of air or other gaseous substances shut 
up or occluded by the carbon is driven out of the 
carbon, which it would be impossible to get rid of 
by the mere operation of pumping. In order to 
insure the success of the operation, it is necessary 
that the heating must take place while the lamp 
is being exhausted, since otherwise the expelled 
gases would be re-absorbed. (See Gas, Occlu- 
sion of. ) 

Both the exhaustion and the incandescence con- 
tinue up to the moment the lamp chamber is 
hermetically sealed; otherwise, some of the air 
might remain in the lamp chamber. 

The lamp chamber is hermetically sealed, 
usually by the fusion of the glass in the manner 




adopted in the sealing of Geissler tubes or 
Crookes' radiometers. 

For the preparation of the carbon strip, its 
carbonization and the flashing of the strip, see 
Carbonization, Processes of. Carbons, Flashing 
Process for. 

The ends of the carbon strip, 
or filament, are attached to lead- 
ing-in wires of platinum that pass 
through the glass walls of the 
lamp chamber, and are fused 
therein by melting the glass 
around them in the same manner 
as are the leading-in wires of the 
Geissler tubes and other similar 
apparatus. 

Incandescent lamps are gener- 
ally connected to the leads or cir- Fig. 334. Incan- 
cuits in multiple-arc or in multi- descent Electric 
pie-series. They are, however, Lamp. 

sometimes connected to the line in series. (See 
Circuits, Varieties of.) 

In the case of multiple-arc or multiple-series 
connection, the resistance of the filament is com- 
paratively high. In the case of series-connec- 
tion the resistance is comparatively low. 

Incandescent electric lamps assume a variety of 
different forms. In all cases, however, the shape 
of the filament is such 
that the leading-in 
wires that carry the 
current to and from 
the filament shall en- 
ter and leave the lamp 
chamber at points that 
are comparatively 
near together. This 
is for the purpose of 
avoiding the unneces • 
sary production of 
shadows. 

Commercial incan- 
descent electric lamps 
are generally marked 
with the potential dif- 
ference in volts that 
must be applied at the 
terminals in order to 
furnish the current 
necessary to properly 
operate them. ' If this 

potential difference is 

, , , Fig, 333. Swan Incandescent 

made greater, the can- Lamp. 




Lam.] 



308 



[Lam, 



.<tle-power of the lamp is greatly increased, but its 
•ife greatly decreased. 

The lamp chamber is more liable in such cases 
V> become less transparent from the deposit of a 
fhin layer of carbon or metal on its inner surfaces. 

In the Swan lamp the filament is made of cot- 
ton thread. These threads are immersed in a 
mixture of two parts of sulphuric acid and one of 
water, which converts the cellulose of the thread 
into artificial parchment. The filaments are rap- 
idly washed as soon as they are removed from the 
sulphuric acid until all traces of the acid are re- 
moved. They are then passed through discs so 
as to insure a uniform area of cross-section, and 
are then wrapped on rods of carbon or earthen- 
ware of the required outline, packed m a crucible 
filled with powdered charcoal, and carbonized. 

The form generally given to the Swan filament 
is that shown in Fig. 335. 

Lamp, Electric, Incandescent Ball 

— An incandescent electric lamp in which 
the light is produced by a sphere or ball of 
carbon placed in an exhausted receiver of 
glass. 

When subjected to the effects of electrostatic 
waves of high frequency of alternation, such a 
lamp becomes luminous 
from the incandescence of 
the carbon ball or sphere. 
Tesla's incandescent ball 
electric lamp is a modifica- 
tion of his straight filament 
lamp. (See Lamp, Incan- 
descent, Straight Filament.} 

The construction of Tes- 
la's ball incandescent elec- 
tric lamp will be readily 
understood from an inspec- 
tion of Fig. 336. 

Lamp, Electric, In- 
candescent, Half-Shades 

for (See Half- 
Shades for Incandescent Lamps?) 

Lamp, Electric, Incandescent, Life of 

The number of hours that an incan- 
descent electric lamp, when traversed by the 
normal current, will continue to afford a good 
commercial light. 

The failure of an electric incandescent lamp 
results either Irom the volatilization or rupture 
of the carbon conductor, or from the failure of the 




Fig: 336. Testa's In- 
candescent Bait Electric 
Lamp. 



vacuum of the lamp chamber. Since the em- 
ployment of the flashing process, and the process 
for removing the occluded gases, it is not unusual 
for incandescent lamps to have a life of several 
thousand hours. (See Carbons, Flashing Pro- 
cess for.) 

The life of an incandescent electric lamp should 
not be considered as continuing until the filament 
actually breaks. As soon as the lamp chamber 
has become covered with such a deposit of car- 
bon or coating of metal as to considerably de- 
crease the amount of light which passes through 
the chamber, the lamp should be considered as 
useless. 

Lamp, Electric, Incandescent, Three- 
Filament, for Multi-Phase Circuits 

— An incandescent lamp for use on multi- 
phase circuits, provided with three leading-in 
wires, connected to the free ends of three 
filaments, the other ends of which are con- 
nected in a common joint. 

When properly acting, the current passing 
through each filament should, at any instant, 
equal the sum of the currents in the other two- 
filaments, which, as is well known, is the property 
of any three-phase circuit. 

Lamp, Electric, Outrigger for 

(See Outrigger for Electric Lamp?) 

Lamp, Electric, Pendant An in- 
candescent electric lamp suspended by flexible 
twin-wire. 

Lamp, Electric, Safety - — —An in- 
candescent electric lamp, with thoroughly 
insulated leads, employed in mines, or other 
similar places, where the explosive effects of 
readily igmtable substances are to be feared. 

Such lamps are often directly attached to a 
portable battery, in which case they can be read- 
ily carried about from place to place. 

Lamp, Electric, Semi-Incandescent 

— An electric lamp in which the light is due 
to the combined effects of a voltaic arc and 
electric incandescence. 

In the Reynier semi- incandescent Ianp, shown 
in Fig. 337, a thin pencd of carbon C, is gently 
pressed against a block of graphite B. A lateral- 
contact is provided at L, through a block of; 
graphite I, by means of which the current is con- 



Lam. J 



309 



LLam. 



veyed to the lower part only of the movable rod 
C, which part alone is rendered incandescent. 
In this lamp, the light is due both to the incan- 

,.C 




33 7« Semi-Incandescent Lamp. 

descence of the rod C, and to the small arc formed 
at J, between its lower end and the contact block 
B, though mainly from the latter. The semi- 
incandescent electric lamp has not as yet been in- 
troduced to any considerable extent. 

Lamp, Electric, Series-Connected Incan- 
descent An incandescent electric lamp 

adapted for use in series circuits. 




Fig, 338. Series Incandescent Electric Lamp. 

A form of series incandescent lamp, attached 
to pendant and shade, is shown in Fig. 338. 

In the series connected incandescent lamp, un- 
like the multiple-connected incandescent electric 
lamp, the resistance of the filament is low. This 
is done ir> order to prevent the total resistancj of 



the circuit from requiring too high an electro- 
motive force for operation. In order to preserve 
the continuity of the circuit on the failure of any 
lamp to operate, some form of automatic cut-out 
is employed. This is generally some form of 
film cut-out. (See Cut- Out, Film.) 

Lamp Hour. — (See Hour, Lamp.) 

Lamp, Incandescent, Electric Filament 

of A term now generally applied to the 

incandescing conductor of an incandescent 
electric lamp, whether the same be of very 
small cross-section or of comparatively large 
cross-section. 

The term filament is properly applied to a con- 
ductor containing fibres or filaments extending in 
the general direction of the length of the incan- 
descing conductor. Such a conductor is made of 
carbonizable fibrous material, cut or shaped prior 
to carbonization so as to have its fibres extend- 
ing with their greatest length in the direction of 
length of the filament. 

Lamp, Incandescent, Straight Filament 

An incandescent electric lamp in. 



which a straight filament, placed in an ex- 
hausted glass chamber, is rendered luminous 
by the effects of electro- 
static waves or thrusts of 
. high frequency. 

The straight filament in 
candescent lamp is the in- 
vention of Tesla. One 
form of such a lamp is 
shown in Fig. 339. 

The glass globe b, of the 
lamp is provided with a 
cylindrical neck, inside of 
which is placed a tube m, 
of conducting material, on 
the side and over the end 
of the insulating plug n. 

The light-giving fila- 
ment e, is a straight car- 
bon stem, connected to the 
plate by a conductor cov- 
ered with a refractory in- 
sulating material k. An 
insulated tube-socket p, 
provided with a metallic lining s, serves to sup- 
port the lamp and connect it with one pole of the 
source of current It will be noticed that the coat- 




Fig> 339- Tesla s 
Straight Filament In- 
candescent Lamp. 



Lam.] 



310 



[Law. 



ings s and m, form the plates of a condenser. 
The other terminal of the machine may be con- 
nected to the metal coated walls of the room, 
or to metallic plates suspended from the ceiling. 
Lamp Indicator. — (See Indicatory Lamp) 

Lamp, Pilot In systems for the 

operation of electric lamps, an incandescent 
lamp employed in a station to indicate the 
difference of potential at the dynamo ter- 
minals, by means of the intensity of its emitted 
light. 

Lamp Rod. — (See Rod, Lamp) 

Lamp Socket Switch. — (See Switch, 
La?np Socket.) 

Lamps, Bank of ■ — A term applied 

to a number of lamps, equal to about half the 
load, that were formerly placed in view of the 
attendant in circuit with a dynamo that is to 
be placed in a parallel circuit with another 
dynamo, one of the lamps of which is also 
in view. 

When the lamps "in bank " were judged to be 
of the same brilliancy as the one fed by the other 
dynamo, the attendant switched the dynamo par- 
allel with the other, and at the same time cut off 
the bank of lamps from the switched in dynamo. 

The method is, however, wrong. The proper 
way is to make the voltage of the dynamo equal 
to that of the circuit. Then connect it and 
-finally raise its electromotive force until it takes 
its share of the load. 

Lamps, Cartooning Placing carbons 

in electric arc lamps. 

When the carbons are consumed, the lamp 
requires recarboning. The old carbon ends are 
replaced by new carbons, and the lamp rods 
cleansed. 

Large Calorie. — (See Calorie, Great) 

Latent Electricity. — (See Electricity, 
Latent) 

Lateral Discharge. — (See Discharge, 
Lateral) 

Lateral Induction. — (See Induction, Lat- 
eral) 

Lateral Leakage of Lines of Magnetic 
Force. — (See Leakage, Lateral, of Lines of 
Magnetic Force) 



Lateral Magnetic Leakage.— (See Leak- 
age, Lateral, of Lines of Magnetic Force) 

Latitude, Magnetic The distance 

a place is situated north or south of the mag- 
netic equator 

All places that have the same magnetic latitude 
have the same value for the magnetic inclination 
and magnetic intensity, or are on the same isocli- 
nal and isodynamic lines. The magnetic latitude 
is the same at all points of a magnetic parallel. 

Launch, Electric A boat, the mo- 
tive power for which is electricity, suitable for 
launching from a ship. 

Up to the present time electric launches have 
been propelled by means of electric motors, driven 
by means of powerful storage batteries. 

A form of electric launch constructed for the 
English Government is shown in Fig. 340. It is 




Fig 340. Electric Launch. 

48^ feet in length over all, by 8 feet 9 inches 
beam, with an average draft of 2 feet 3 inches. 
Its speed is 8 knots per hour. It will carry forty 
fully equipped soldiers. 

Law, J acobi's The maximum work 

done by a motor is reached when the counter- 
electromotive force is equal to one-half of the 
impressed electromotive force, or, 

E = i 

2 

Law, Joule's The heating power of 

a current is proportional to the product of 
the resistance and the square of the current 
strength. (See Heat, Electric) 

Law, Natural A correct expression 

of the order in which the causes and effects 
of natural phenomena follow one another. 

The law of gravitation, for example, correctly 
expresses the order of sequence of the phenomena 
which result when unsupported bodies fall to the 
earth. It should be carefully borne in mind, how- 
ever, that natural laws cannot be regarded as 
explaining the ultimate causes of natural pheno- 



Law.] 



311 



[Law, 



mena, but merely express their order of occur- 
rence or sequence. 

We are ignorant, for example, of the true cause 
of gravitation and are only acquainted with its 
effects. This is true of all ultimate physical 
causes, save for our belief in their origin in a 
Divine will. 

Law of Electro-Chemical Equivalence. 
— (See Equivale?ice, Electro-Chemical, Law 
of) 

Law of Kohlrausch. — In electrolytic con- 
duction, each atom has a rate of motion for 
a given liquid, which is independent of the 
element with which it may have been com- 
bined. 

In the following table, the rate of motion of 
various kinds of atoms through nearly pure water 
for a difference of potential of one volt per linear 
centimetre, is given: 

H I.08 centimetres per hour. 

K 0.205 centimetre " 

Na 0.126 

Li 0.094 

Ag 0.166 

C 0.213 

1 0.216 

K0 3 0.174 

Law of Olim, or Law of Current 
Strength. — The strength of a continuous 
current is directly proportional to the differ- 
ence of potential or electromotive force in the 
circuit, and inversely proportional to the re- 
sistance of the circuit, i. e., is equal to the 
quotient arising from dividing the electromo- 
tive force by the resistance. 






H 



' r ' •*■ " r> 

Fig. 34.T. Current Strength in Circuit. 



Ohm's law is expressed algebraically thus: 
or, E = C R. 



C = 5; 



R 

If the electromotive force is given in volts, and 
the resistance in ohms, the formula will give the 
current strength directly in amperes. 



The resistance of any electric circuit, as, for 
example, that shown in Fig. 341, consists of three 
parts, viz. : 

(1.) The internal resistance of the source, r. 

(2.) That of the conducting wires or leads, r' ; 
and 

(3.) That of the electro-receptive, r", energized 
by the current. Ohm's law applied to this case 
would be: 

E 
C = r + r'+r". 

That is, the resistance of the entire circuit is 
equal to the sum of the separate resistances of its 
different parts. 

Since C= -, (1); then E = C R, (2); 



R 



and R 



(3)- 



But, since a current of one ampere is equal to 
one coulomb per second, then, in order to deter- 
mine in coulombs the quantity of electricity pass- 
ing in a given number of seconds, itisonly neces- 
sary to multiply the current by the time in seconds, 
orQ = CT( 4 ). 

Hence, referring to the above equations (1), 
(2), (3) and (4); according to Ohm's law: 

(1.) The current in amperes is equal to the 
electromotive force in volts divided by the resist- 
ance in o/ims. 

(2.) The electromotive force in volts is equal to 
the product of the current in amperes and the 
resistance in ohms. 

(3.) The resistance in ohms is equal to the elec- 
tromotive force in volts divided by the current in 
amperes. 

(4.) The quantity of electricity in coulombs is 
equal to the current in amperes multiplied by the 
time in seconds. 

Law of Volta, or Law for Contact-Series. 

— A law for the differences of electric potential 
produced by the contact of dissimilar metals 
or other substances. 

" The difference of potential between any two 
metals is equal to the sum of the differences of 
potential between the intervening substances in 
the contact series." (See Electricity, Contact. 
Series, Contact.) 

Law, Pfl user's A given tract of 

nerve is stimulated by the appearance of 
kathelectrotonus and the disappearance of an- 
electrotonus ; not, however, by the disap- 



Law. J 



312 



Law, 



pearance of kathelectrotonus nor by the ap- 
pearance of anelectrotonus. — (Landois and 
Stirling?) 

Law, Pointing's —At any point in 

a magnetic field, or a conductor conveying 
current, the energy moves perpendicularly to 
the plane containing the lines of elec+ric force 
or the lines of magnetic force, and the amount 
of energy crossing the unit of area of this 
plane per second is equal to the product of 
the intensities of the two forces multiplied by 
the sine of the angle between them, divided 
by 47t. 

If E, represents the electric force of a small body 
charged with positive electricity, and H, the 
magnetic force or forces of a smaller free unit 
north pole, and, if these forces at any point in 
the magnetic field are inclined at an angle, 0, 
then e, the flow of energy per second at this point, 
in a direction oerpendicular to the planes of E and 
His, 

E H sin. 9 

e = -. 

There is, therefore, a difference in the direction 
of the flow of electricity and the flow of electric 
energy. Electricity may be conceived as passing 
through the conductor something like water 
through a pipe, but electrical energy does not 
travel in this way. Electrical energy travels 
through the surrounding dielectric, which is 
thereby strained, and it propagates this strain 
from point to point until it reaches the conductor 
and is there dissipated. 



Law, Toltametric 



-The chemical 



action produced by electrolysis in any elec- 
trolyte is proportional to the amount of elec- 
tricity which passes through the electrolyte. 

This is called the Voltametric law, because any 
vessel' containing an electrolyte, and furnished 
with electrodes, so that electrolysis may take place 
on the passage of the current, and is provided 
with means for measuring the amount of the 
electrolysis which occurs, is called a Voltameter. 
(See Voltameter. Electrolysis.) 

Laws, Ampere's, or Laws of Electro- 
Dynamic Attraction and Repulsion 

Laws expressing the attractions and repul- 
sions of electric circuits on one another or 
on magnets. 



Laws, Dub's '• The magnetism ex- 
cited at any transverse section of a magnet is 
proportional to the square root of the distance 
between the given section and the near end 
of the magnet." 

" The free magnetism at any given trans- 
verse section of a magnet is proportional to 
the difference between the square root of half 
the length of the magnet and the square root 
of the distance between the given section and 
the nearest end." 

Laws, Kirchhoff's —The laws for 

branched or shunted circuits. 

These laws may be expressed as follows: 

(I.) In any number of conductors meeting at a 
point, if currents flowing to the point be considered 
as -[-, and those flowing away from it as — , the 
algebraic sum of the meeting currents will be 
zero. 

This is the same thing as saying as much elec- 
tricity must flow away from the point as flows to- 
ward it. 

(2.) In any system of closed circuits the alge- 
braic sum of the products of the currents into the 
resistances is equal to the electromotive force ia 
the circuit. 

In this case all currents flowing in a certain 
direction are taken as positive, and those flowing 
in the opposite direction as negative. All elec- 
tromotive forces tending to produce currents in 
the direction of the positive current are taken as 
positive, and those tending to produce currents in 
the opposite direction, as negative. 

E 
This follows from Ohm's law ; for, since C = — , 

R 
the electromotive force E = CR, and this is true, 
no matter how often the circuit is branched. 



Laws, Lenz's 



-Laws for determining 



the directions of currents produced by electro- 
dynamic induction. 

The direction of the currents set up by electro- 
dynamic induction is always such as to oppose 
the notions by which such currents were pro- 
duced. 

Laws of Becquerel, or Laws of Mag- 
neto-Optic Rotation. — Laws for the mag- 
neto-optic rotation of the plane of polarization 
of light. (See Rotation, Magneto-Optic?) 

Laws of Coulomb, or Laws of Electro- 



Xaw.j 



313 



[Lea. 



static and Magnetic Attractions and Re- 
pulsions.— Laws for the force of attraction 
and repulsion between charged bodies or be- 
tween magnet poles. 

The fact that the force of electrostatic attrac- 
tion or repulsion between two charges, is directly 
proportional to the product of the quantities of 
electricity of the two charges and inversely propor- 
tional to the square of the distance between them, 
is known as Coulomb's Law. Coulomb also as- 
certained that the attractions and repulsions be- 
tween magnet poles are directly proportional to the 
product of the strength of the two poles, and in- 
versely proportional to the square of the distance 
between them. This is also called Coulomb's 
Law. 

Coulomb's law, in order to be accurate, must 
take into account the specific inductive capacity 
of the intervening medium. The correct expres- 
sion for the force between two quantities q and q', 
of electricity would be, therefore, 



F = 



qq 



r*K' 

where K, is equal to the specific inductive capacity 
of the medium separating the two charges. 

In a similar manner when the force is exerted 
between two magnet poles, to be accurate, we must 
take into account the magnetic permeability of 
the medium between the two magnets. The cor- 
rect expression for the force between two magnet 
poles is, therefore, 

when ju, is the magnetic permeability. 

Laws of Faraday, or Laws of Electrolysis 

Laws for the effects of electrolytic 

decomposition. (See Electrolysis) 

These laws are as follows: 

(i.; The amount of an electrolyte decomposed 
is directly proportional to the quantity of elec- 
tricity which passes through it ; or, the rate at 
which a body is electrolyzed is proportional to 
the current strength producing such electrolysis. 

(2.) If the same current be passed through dif- 
ferent electrolytes, the quantity of each ion 
evolved is proportional to its chemical equivalent. 

Laws of Joule. — Laws expressing- the de- 
velopment of heat produced in a circuit by an 
electric current. 

These laws may be expressed as follows : 

(i.) The amount of heat developed in any cir- 



cuit is proportional to its resistance, providing 
the current stiength is constant. 

(2. ) The amount of heat developed in any cir- 
cuit is proportional to the square of the current 
passing, providing the resistance is constant. 

(3.) The amount of heat developed in any cir- 
cuit is proportional to the time the current con- 
tinues. 

Or, H = C2 Rt XO.24. 

Where H, equals the heat in small calories, C, 
equals the current in amperes, R equals the re- 
sistance in ohms, t, equals the time in seconds, 
and 0.24, the heat-units per second developed in 
a resistance of I ohm by the passage of 1 am- 
pere. 

Lay Torpedo.— (See Torpedo, Lay) 

Layer, Crookes' —A layer, or 

stratum, of the residual atmosphere of a 
vacuous space, in which the molecules, recoil- 
ing from a heated or electrified surface, do 
not meet other molecules, but impinge on the 
walls of the vessel directly opposite such 
heated or electrified surface. 

A Crookes layer may result as the effect of 
two different causes, viz. : 

(I.) The rarefaction of the gas is such that the 
distance between the walls of the vessel and the 
heated surface is less than the mean-free-path of 
the molecules. 

(2.) The wall is so near the heated surface that 
the distance between the two is less than the ac- 
tual mean-free-path of the molecules. Under 
these last-named circumstances Crookes' layers 
may result, whatever be the density of the gas. 

Laying-Up CaMes. — (See Cables, Lay- 
ing- Up) 

Lead, Angle of The angular devia- 
tion from the normal position, which must be 
given to the collecting brushes on the com- 
mutator cylinder of a dynamo-electric ma- 
chine, in order to avoid destructive burning. 
(See Commutator, Bur7ting at) 

The necessity for giving the collecting brushes 
a lead, arises both from the magnetic lag and from 
the distortion of the field of the machine by the 
magnetization of the armature current. The 
angle of lead is, therefore, equal to the sum of the 
angle of lag, and the angular distortion due to the 
magnetization produced by the armature current. 



Lea.] 



314 



[Lea* 



Lead, Cable A lead containing a 

conductor formed of several stranded con- 
ductors, as distinguished from a wire lead or 
a lead containing a single conductor. 

Lead, Flexible A conductor formed 

of a number of small stranded conductors for 
the purpose of obtaining flexibility. 

Lead, Flexible Twin — A flexible 

conductor in which two parallel and sepa- 
rately insulated wires are placed. 

Lead of Brushes of Dynamo-Electric 
Machine. — The angular deviation from the 
normal position, which it is necessary to give 
the brushes on the commutator of a dynamo- 
electric machine, in order to obtain efficient 
action. (See Lead, Angle of) 

Lead Scoring Tool. — (See Tool, Scoring, 
Lead) 

Lead Sleeve. — (See Sleeve, Lead.) 

Lead, Tee.— (See Tee, Lead.) 

Lead, Wire A lead consisting of a 

single conductor, as distinguished from a 
cable lead, or a lead containing a number of 
stranded conductors. 

Lead Wire.— (See Wire, Lead) 

Leading Horn of Pole Pieces of Dynamo- 
Electric Machine. — (See Horns, Leadmg, of 
Pole Pieces of a Dynamo-Electric Machine.) 

Leading-In Wires. — (See Wires, Lead- 
ing-In) 

Leading-Up Wires. — (See Wires, Lead- 
ing- Up) 

Leads. — The conductors in any system of 
electric distribution. 

In distribution by parallel, the conductors 
through which the current flows from the source 
are sometimes called the leads in contradis- 
tinction to those through which it returns to 
the source. 

The leads, or main conductors, in a multiple 
system of electric lighting, must maintain a con- 
stant potential at the lamp terminals. The dimen- 
sions of the leads are, therefore, so proportioned as 
to absorb as small an amount of potential as pos- 
sible. Since, in incandescent lighting, where the 
lamps are connected to the leads in multiple-arc, 
the total resistance of the lamps is comparatively 



small, the resistance of the leads must be quite 
small in order to avoid a marked drop of poten- 
tial. Comparatively large conductors must, 
therefore, be used. 

The main conductor for series circuits, such as 
for arc -lights, has in all parts the same current 
strength. Since the sum of the resistances of the 
lamps in such a circuit is quite high, a compara- 
tively high resistance in the conductor may be 
employed without a proportionally large absorp- 
tion of potential. Comparatively small conduc- 
tors can therefore be used. (See Electricity, Dis- 
tribution of, by Constant Currents. Electricity, 
Distribution of, by Alternating Currents.') 

Leads, Armature, Twist in A dis- 
placement of the ends of the wires connected 
to the commutator segment, with respect to 
the position of the coils on the armature, for 
the purpose of obtaining a more convenient 
position for the diameter of commutation, 
that is, for the collecting brushes. 

Leak, Oscillatory A leak or grad- 
ual loss of electricity which takes place in 
alternately opposite directions.' 

Leak, Unidirectional A gradual 

loss or leakage of electricity which takes place 
in one and the same direction. 

The term has been employed to distinguish 
such a leak from an oscillatory leak. 

Leakage Conductor. — (See Con irfir, 
Leakage) 

Leakage, Electric — The gradual 

dissipation of a current due to insufficient in- 
sulation. 

Some leakage occurs under nearly all circum- 
stances. On telegraphic lines, during wet 
weather, the leakage is often so great as to inter- 
fere with the proper working of the lines. 



-The grad- 



Leakage, Electrostatic — 

ual dissipation of a charge due to insufficient 
insulation. 

The leakage of a well insulated conductor, 
placed in a high vacuum, is almost inappreciable. 
Crookes has maintained electric charges in high 
vacua for years without appreciable loss. 

Leakage, Lateral, of Lines of Magnetic 
Force The failure of lines of magnetic 



Lea.] 



315 



[Leu. 



force to pass approximately parallel to one 
another through a bar of iron or other mag- 
netizable material, when it has come to rest 
in a magnetic field in which it is free to 
move. 

The escape of the lines of magnetic force 
from the sides of a bar or other similar 
magnet, instead of from the poles at the 
end. 

When a bar of magnetizable material, sus- 
pended so as to be free to move, comes to rest in 
a magnetic field in which it is undergoing mag- 
netization, it has its greatest length parallel to 
the direction of the lines of force. If the bar is a 
long, thin, straight bar, the lines of force do not 
all pass in or come out at its ends. On the con- 
trary, many of these lines of force or induction 
pass in or come out at other points. The mag- 
netic induction is, therefore, unequal at different 
sections of the bar. In other words, the mag- 
netic flux or intensity is not constant per unit of 
all cross-sections of such bar. 

Leakage, Magnetic A useless dis- 
sipation of the lines of magnetic force of a 
dynamo-electric machine, or other similar 
device, by their failure to pass through the 
armature where they are needed. 

Useless dissipation of lines of magnetic 
force outside that portion of the field of a 
dynamo-electric machine through which the 
armature moves. 

Such a leakage can be detected by an instru- 
ment called a magnetophone. (See Magneto- 
phone.) 

Magnetic leakage results in lowering the effi- 
ciency of the dynamo. (See Co-efficient, Econo- 
mic, of a Dynamo-Electric Machine. ) 

Leclanche's Yoltaic Cell.— (See Cell, 
Voltaic, LccLmche.) 

Leg". — In a system of telephonic exchange, 
where a ground return is used, a single wire, 
or, where a metallic circuit is employed, two 
wires, for connecting a subscriber with the 
main switchboard, by means of which any 
subscriber may be legged or placed directly 
in circuit with two or more other parties. 

Leg of Circuit. — (See Circuit, Leg of.) 

Legal Earth Quadrant.— (See Quadrant, 
Legal Earthy 



Legal Ohm.— (See Ohm, Legal.) 

Legging-Key Board.— (See Board, Leg- 
ging-Key.) 

Length of Spark.— (See Spark, Le7igtk 
of.) 

Lens, Achromatic A lens the 

images formed by which are free from the 
false coloration produced in other lenses by 
dispersion. 

An ordinary lens can be rendered approxi- 
mately achromatic by the use of a diaphragm. 
Achromatic lenses generally consist of the com- 

D 




Fig. 342. 



A c 

Equal and Opposite Refracting Angles. 



bination of a double convex lens of flint glass and 
a concave lens of crown glass. 

The ray of light entering the prism ABC, 
Fig. 342, suffers dispersion (separation into pris- 
matic colors). This dispersion in the same 
B Q 




A C 

Fig. 343. Principle of Achromatism, 

medium is proportional to the angle g, between 
the incident and emergent faces, called the re- 
fracting angle. 

If, now, another prism B C D, of the same ma- 
terial, with a refracting angle g', equal to g, is 
combined with the first prism in the manner 
shown in Fig. 342, it will produce an equal but 
opposite dispersion, so that the ray of light will 
emerge at R', free from rainbow tints, but par- 
allel to its original direction. 

The variety of glass called crozvn glass pro- 
duces only half as great dispersion of light as the 
variety called flint glass, under the same refract- 



Xen.] 



316 



[Lig. 



ing angle g. If the prism A B C, of crown glass, 
Fig. 343, whose angle g, is twice as great as the 
refracting angle g , of the prism B C D, of flint 
glass, be placed together in the manner shown, 
then the ray R, will be transmitted at R', free from 
color, but will not emerge par ailed to its original 
direction ; in other words, it suffers refraction or 
bending. Consequently such a combination can 
be used to free a pencil of light from false colora- 
tion and yet permit it to undergo refraction, 
and thus act as a lens. (See Refraction.) 

The construction ot achromatic lenses is based 
on this principle. 

The crown glass is generally made with two 





Fig. 344. Piano-Convex 
Achromatic Lens. 



Fig- 345' Achromatic 
Lens. 



convex surfaces ; the flint glass, with one con- 
cave and one plane surface, as shown in Fig. 

344- 

Sometimes both surfaces of the flint glass are 
made curved, as in Fig. 345. 

Lenz's Law. — (See Law, Lcnz's) 

Letter Box, Electric A device 

that announces the deposit of a letter in a 
box by the ringing of a bell, or by the move- 
ment of a needle or index. 

These devices generally act by the closing or 
opening of an electric circuit on the fall of the 
letter into the box. 



Leyden Jar. — (See far, Ley den) 

Ley den Jar Fattery. — (See Battery, Ley- 
den far.) 

Lichtenberg's Dust Figures,— (See Fig- 
ures, Lichtenbergs Dust) 

Life Curve of Incandescent Electric 
Lamp. — (See Curve, Life, cf Incandescent 
Electric Lamp) 

Life of Electric Incandescent Lamp. — 
(See Lamp, Inca7idescent, Life of.) 

Light, Auroral The light given off 

during the prevalence of an aurora. (See 
Aurora Boreal is.) 

Light, Electric Light produced by 

the action of electric energy. 

Electric light is produced by electric energy in 
various ways, the most important of which are as 
follows, viz.: 

(1.) By the passage of an electric discharge 
through a gas or vapor, either in a rarefied condi- 
tion, at ordinary atmospheric pressure, or at pres- 
sures higher than that of the ordinary pressure. 
In any of these cases the gas or vapor is heated to 
incandescence by the passage of the discharge. 

(2.) By the incandescence of a solid by the 
heating power of the current, as in the incandes- 
cent lamp. 

(3.) By the incandescence of a solid by the ac- 
tion of a rapidly alternating electrostatic field, as 
in Tesla's incandescent lamp. 

(4 ) By the volatilization of a solid and the form- 
ation thereby of a voltaic arc. 

(5.) By the combination of the effects of incan- 
descence and the voltaic arc. 

The amount of light produced in proportion to 
the amount of energy expended to produce it 
is probably least in the case of light produced 
by the sparks of a Wimshurst or Holtz machine, 
or as in (1), than in any other case in which electric 
energy acts to produce luminous energy. 

Light, Electric, Pumping of (See 

Pumping of Electric Light) 

Light, Intensity of The brilliancy 

or illuminating power of a light as measured 
by a photometer in standard candles or other 
standard units. (See Photometer. Candle, 
Standard) 

Light, Maxwell's Electro - Magnetic 
Theory of — A hypothesis for the 



lig.] 



317 



[Lig. 



cause of light proposed by Maxwell, based 
on the relations existing between the phe- 
nomena of light and those of electro-magnet- 
ism. 

Maxwell's electro-magnetic theory of light as- 
sumes that the phenomena of light and magnet- 
ism are each due to certain motions of the ether, 
electricity and magnetism being due to its rota- 
tions, and light to oscillations, or its to-and-ffo 
motions. 

Maxwell proposed this theory to show that the 
phenomena of light, heat, electricity and magnet- 
ism could all be explained by one and the same 
cause, viz., a vibratory or oscillatory motion of 
the particles of the hypothetical ether. Maxwell 
died before completing his hypothesis, and it has 
never since been sufficiently developed to thor- 
oughly entitle it to the name of a theory. This 
theory has more recently been elaborated by 
Hertz. (See Electricity \ Hertz 's Theory of Elec- 
tro-Magnetic Radiations or Waves .) 

There are, however, numerous considerations 
which render it probable that electric and mag- 
netic phonomena, like those of light and heat, 
have their origin in a vibratory or oscillatory mo- 
tion of the luminiferous ether. A few of these, 
as pointed out by Maxwell, S. P. Thompson, 
Xodge, Larden and others, are as follows: 

(i.) It is possible that the thing called elec- 
tricity is the ether itself, negative electrification 
consisting in an excess of the ether, and positive 
electrification in a drficit. (See Electricity ', Sin- 
gle-Fluid Hypothesis of. ) 

(2.) It is possible that electrostatic phenomena 
consist in a strain or deformation of the ether. 
A dielectric may differ from a conductor in that 
the former may have such an attraction for the 
ether as to give it the properties of an elastic 
solid, while in the latter the ether is so free to 
move that no strain can possibly be retained by 
it. (See Dielectric. Conductor.) 

(3.) Dielectrics are transparent and conductors 
are opaque. 

There are exceptions to this in the case of vul- 
canite and many other excellent dielectrics. Nor 
should this similarity be expected to be general in 
view of the well known differences that exist be- 
tween diathermancy and transparency. 

(4.) It is possible that an electric current con- 
sists of a real motion ot translation of the ether 
ihrough a conductor. 

(5.) It is possible that electromotive force re- 



sults from differences of ether pressures. This 
would of course follow from (4). 

(6.) The vibrations of light are propagated in 
a direction at right angles to the direction in 
which the light is moving. The magnetic field 
of a current is propagated in planes at right 
angles to the direction in which the current is 
flowing. 

(7.) It is possible that lines of electrostatic and 
magnetic force consist of chains of polarized ether 
particles. 

(8. ) The velocity of propagation of light agrees 
very nearly with the velocity of propagation of 
electro-magnetic induction. (See Ratio Velocity.) 

(9. ) In certain axial crystals the difference of 
transparency in the direction of certain axes, 
corresponds with the direction in which such 
crystals conduct electricity. 

Recent investigations render it almost certain 
that light and electro-magnetic waves or radia- 
tions are one and the same, and, therefore, have 
the same velocity of propagation through free 
ether. Through fixed ether, that is, through the 
ether that exists between the molecules of differ- 
ent kinds of matter, as is well known, the velocity 
of propagation differs with different substances. 
(See Electricity, Hertz's Theory of Electro-Mag- 
netic Radiations or Waves. ) 

Light, Northern (See Aurora 

Borealis.) 

Light, Platinum-Standard —The 

light emitted by a surface of platinum one 
square centimetre in area, at its temperature 
of fusion. 

This is called the Violle Standard and is ex- 
tensively used in France. 

Light, Search, Automatic A search 

light in which a parallel or slightly diverging 
beam of light is automatically caused to 
sweep the horizon, and thus disclose the ap- 
proach of a torpedo boat or other similar 
danger. 

This is called an automatic search light because 
it may be caused to automatically sweep the hori- 
zon, instead of being manipulated by hand, as 
usual. 

— An electric 



Light, Search, Electric — 

arc light placed in a focusing lamp before a 
lens or mirror, so as to obtain either a parallel 
beam or a slightly divergent pencil of light 



Lig.] 



318 



LLig. 



for lighting the surrounding space for pur- 
poses of exploration. 

Light, Southern — (See Aurora 

Australis.) 

Light, Tail A light displayed at the 

rear end of trains in order to avoid rear colli- 
sions. (See Railroads, Block System for.) 

Lighter, Cigar, Electric An ap- 
paratus for electrically lighting a cigar. 

A cigar lighter consists essentially of a wire or 
rod of refractory substance, rendered incandes- 
cent by the passage of a current obtained from a 
voltaic battery, secondary generator, or other 
electric source. 

Lighter, Electric, Argand A name 

sometimes given to an argand electric plain- 
pendant burner. (See Burner, Argand- 
Electric, Plain-Pendant.) 

Lighter, Electric, Argand Talve 

A name sometimes given to an argand elec- 
tric ratchet-pendant burner. (See Burner, 
Argand-Electric, Ratchet-Pendant.) 

Lighthouse Illumination, Electric 

- — (See Illumination, Lighthouse, Electric.) 

Lighting, Arc Artificial illumina- 
tion obtained by means of an arc light. 

The term arc lighting is used in contradistinc- 
tion to incandescent lighting. In the United 
States, and, indeed, generally, a number of arc 
lights are placed in series on the line circuit, con- 
nected generally with a series dynamo. Each 
of the lamps is provided with a safety cut-out, 
which cuts out or removes a defective lamp from 
the circuit by automatically turning or switching 
the current through a shunt of low resistance. 

Lighting, Electric, by High Frequency 

Currents —A system of electric lighting, 

in which rods, bars or filaments of carbon or 
other refractory substances are raised to in- 
candescence when placed in a rapidly alternat- 
ing electrostatic field. 

This system of electric lighting was invented 
by Nikola Tesla. Its general principles will be 
understood from an inspection of Fig. 346. 

G, is a dynamo producing alternating currents 
of comparatively low potential. A portion of its 
current P, acting as the primary of an induction 
coil, induces alternating currents of high 



potential in the secondary circuit S, which,, 
charging the condenser C, is disruptively dis- 
charged into the circuit A, provided with an air 
gap at A' through P'. The inductive action 
of P', on S', produces oscillatory currents of 



/WWW\A 

mwwimmm 
_ s 



a'WWWW' 

wwwmmmn m 







Fig 346- 



Tesla' s High Frequency Currents 
System of Lighting. 



enormous frequency and potential in the second- 
ary circuits connected therewith. In the ap- 
paratus shown in Fig. 346, two incandescent 
electric lamps are connected with the secondary 
circuit, one with a single straight filament, and 
the other with a ball conductor. The other 
terminal of S', is connected to the walls of the 
room to be lighted. (See Lamp, Incandescent, 
Straight Filament. Lamp, Electric, Incandes- 
cent Ball.) 

Lighting, Electric, Central Station 

— The lighting of a number of houses or other 
buildings from a single station, centrally lo- 
cated. 

Central station lighting is distinguished from iso- 
lated lighting by the fact that a number of sepa- 
rate buildings, houses or areas, are lighted by the 
current produced at a single station, centrally 
located, instead of from a number of separate 
electric sources located in each of the houses, etc., 
to be lighted. (See Electricity, Distribution of.) 

Lighting, Electric Gas Igniting 

gas jets by means of electric discharges. 

Electric sparks are caused to pass through a 
jet of escaping gas, and thus to light it. These 
sparks are obtained from a spark-coil, i. e., a 
coil of insulated wire connected in series with 
the circuit so as to produce an extra current on 
the sudden breaking of the circuit, the discharge 
of which produces a spark capable of igniting the 
gas. In cases where a number of burners are to 
be simultaneously lighted the sparks required for 



Lig.] 



319 



[Lig. 



lighting the gas are obtained from the secondary 
of an induction coil. (See Burner, Automatic 
Electric.) 

Lighting, Electric, Isolated A 

system of electric lighting where a separate 
electric source is placed in each house or 
area to be lighted, as distinguished from the 
central station lighting, where electric sources 
are provided for the production of the current 
required for an entire neighborhood. 

Lighting, Electric, Lo«g-Arc System of 

A system of electric lighting in which 



long arcs are maintained between the carbon 
electrodes. 

Lighting, Electric, Short-Arc System 

A system of electric lighting in which 

short voltaic arcs are maintained between the 
carbon electrodes. 

Systems of short arcs require an electromotive 
force of about 25 volts, which is about one-half 
that employed in long arcs. To develop an 
equal amount of heat energy in a short arc as in 
a long arc, therefore, requires that the current be 
of double strength. 

The greater part of the light of a voltaic arc 
is given off from a tiny crater, which is formed in 
the end of the positive carbon. In the short arc 
system the crater lies so near the negative carbon 
that much of its light is necessarily obscured, and 
troublesome shadows are sometimes produced, 
The long-arc system avoids these difficulties. 

Lightning. — The spark or bolt that results 
from the disruptive discharge of a cloud to 
the earth, or to a neighboring cloud. (See 
Electricity, Atmospheric. Kite, Franklin's?) 

Lightning Arrester.— (See Arrester, 
Lightning?) 

Lightning, Back-Stroke of An 

electric discharge, caused by an induced 
charge, which occurs after the direct dis- 
charge of a lightning flash. 

The shock is not caused by the lightning flash 
itself, but most probably by a charge which is in- 
duced in neighboring conductors by the discharge. 
A similar effect may be noticed by standing near 
the conductor of a powerful electric machine, 
when shocks are felt at every di-chirge. 

The back-stroke has been ascribed by many to 



the oscillations by which a disruptive discharge 
is effected. (See Discharge, Oscillating.) 

The effects of the return shock are sometimes 
quite severe. They are often experienced by 
sensitive people, on the occurrence ot a lightning 
discharge, at a considerable distance from the 
place where the discharge occurred. 

In some instances, the return stroke has been 
sufficiently intense to cause death. In general, 
however, its effects are much less severe than 
those of the direct lightning discharge, 

Lightning, Ball A name some- 
times given to globular lightning, (See 
Lightning, Globular.) 

Lightning, Chain A variety of 

lightning flash in which the discharge takes 
a rippling path, somewhat resembling a 
chain. 

Lightning Conductor.— (See Rod, Light- 
ning?) 

Lightning, Forked A variety of 

lightning flash, in which the discharge, on 
nearing the earth or other object, divides into 
two or more branches. 

Lightning, Globular A rare form 

of lightning, in which a globe of fire appears, 
which quietly floats for a while in the air- and 
then explodes with great violence. 

The exact cause of globular lightning is un- 
known. Phenomena allied to it, however, have 
been observed by Plante during the series dis- 
charge of his rheostatic machine. Similar pheno- 
mena are sometimes, though rarely, observed 
during the discharge of a powerful Leyden battery. 
Sir Wm. Thomson ascribes the effect to an optical 
illusion due to the persistence of the visual impres^ 
sion of a bright flash. This, however, would not 
account for the explosion which almost invariably 
attends globular lightning. 

Lightning Guard. — (See Guard, Light- 
ning.) 

Lightning, Heat A variety of 

lightning flash in which the discharge lights 
up the surfaces of the neighboring clouds. 

Sheet lightning is unaccompanied by thunder. 
It may be regarded as a brush discharge from one 
cloud to another. 

Heat lightning is a variety of sheet lightning.. 
(See Lightning, Sheet.) 



Kg.] 



320 



[Lin. 



Lightning Jar. — (See Jar, Lightning?) 
Lightning", Return-Stroke of A 

term sometimes applied to the back-stroke of 
lightning. (See Lightning, Back-Stroke of) 

Lightning Rod. — (See Rod, Lightning) 

Lightning Rod for Ships.— (See Rod, 
Lightning, for Ships.) 

Lightning, Sheet A variety of 

lightning flash unaccompanied by any thunder 
audible to the observer, in which the entire 
surfaces of the clouds are illumined. 

The cause of sheet lightning has been ascribed 
to reflection from clouds of lightning flashes 
that occur too far bilow the horizon either to 
permit them to be directly seen, or the thunder 
to be heard. 

If a Geissler tube, which contains several con- 
centric tubes, be charged by a Holtz machine, 
and then touched at different parts by the hands, 
a succession of luminous discharges will be seen 
in the dark, that bear a remarkable resemblance 
to the flashes of heat or sheet lightning. 

Lightning Stroke. — (See Stroke, Light- 
ning.) 
Lightning Stroke, Back or Return 

— (See Stroke, Lightning, Back or Return) 

Lightning, Summer A name some- 
times given to heat lightning. (See Light- 
ning, Heat) 

Lightning, Yolcanic The lightning 

discharges that attend most volcanic erup- 
tions. 

Volcanic lightning is possibly sometimes due to 
the friction of volcanic dust particles against one 
another, or against the air, but is more probably 
caused by the sudden condensation of the water 
vapor that is generally disengaged during volcanic 
eruptions. 

Lightning, Zigzag The common- 
est variety of lightning flashes, in which the 
discharge apparently assumes a forked zig- 
zag, or even a chain-shaped path. 

This form is seen in the discharge of a Holtz 
machine, or of a Ruhmkorff Induction Coil. 

Photographic pictures of such lightning dis- 
charges appear to show that these discharges are 
in reality zigzag curves, rather than sharp angu- 
lar zigzags. 



Limiting Stop. — (See Stop, Limiting) 

Limb, Rheoscopic A term some- 
times applied to a sensitive nerve muscle prep- 
aration, employed to detect the presence of 
an electric current. (See Frog, Galvano- 
scope.) 

Line. — A wire or other conductor connect- 
ing any two points or stations. 

Line, Aclinic A line connecting 

places on the earth's surface which have no 
magnetic inclination. 

The magnetic equator of the earth. (See 
Equator, Magnetic) 

Line Adjuster. — An instrument invented 
by Delany for overcoming the effects of leak- 
age on the adjustment of the relays in a way 
line. 

When any key is opened, the line circuit is 
simultaneously broken at both ends so that there 
is a moment of no current, which causes all the 
relays to respond. 

Line, Aerial An air line as dis- 
tinguished from an underground conductor. 

Line, Agonic A line connecting 

places on the earth's surface where the mag- 
netic needle has no declination, or where it 
points to the true geographical north. (See 
Agonic.) 

Line, Artificial A line so made up 

by condensers and resistance coils as to have 
the same inductive effects on charging or dis- 
charging as an actual telegraph line. 

In duplex telegraphy by the differential method, 
the artificial line used must have its capacity 
balanced against that of the line, so as to avoid 
the effects of self-induction, and other effects pro- 
duced by charging and discharging. 

Line, Capacity of The ability of a 

line or cable to act like a condenser, and 
therefore like it to possess a capacity. (See 
Cable, Capacity of.) 

Line Circuit. — (See Circuit, Line) 

Line Circuit, Telegraphic (See 

Circuit, Line, Telegraphic) 

Line, Neutral, of a Magnet A line 

joining the neutral points of a magnet or 



Lin. 



321 



[Liu. 



points approximately midway between the 
poles. 

This is sometimes called the equator of the 
magnet. 

The neutral point is the point where the lines 
of force outside the magnet extend parallel to the 
surface of the magnet.— {Hering.) 
Line, Neutral, of Commutator Cylinder 

A line on the commutator cylinder of 

a dynamo-electric machine connecting the 
neutral points, or the points of maximum 
positive and negative difference of potential. 
(See Machine, Dynamo-Electric!) 

Line of Least Sparking.— (See Sparking, 
Least Line of.) 

Line, Single-Wire A term some- 
times used for a solid-wire conductor. (See 
Line, Solid.) 

Line, Solid — A line formed of a 

single conductor, as distinguished from a line 
formed of several conductors or by a stranded 
cable. 

Line, Stranded A line formed of 

several strands or separate conductors twisted 
into one. 

Line, Telegraphic, Telephonic, etc. 

— The conducting circuit provided for the 
transmission of the electric impulses or cur- 
rents employed in any system of electric 
transmission. 

Line, Telpher The conducting line 

used in a system of telpherage. (See Tel- 
phe? age.) 

Line, Through A line extending 

between two terminal points, as distinguished 
from a line containing way stations. 

Line, Trunk — In a system of tele- 
phonic communication any line connecting 
distant stations and used by a number of 
subscribers at each end for purposes of inter- 
communication. 

Line, Way A line communicating 

with way stations. 

Line Wire. — (See Wire, Line!) 

Lineman. — One who puts up and repairs 
line circuits and attends to the devices con- 
nected therewith. 



In a system of electric lighting the lineman 
attends to carboning the lamps, cleaning the 
lamp rods, and, generally, to the minor details of 
the lines, insulators and the electro-receptive de- 
vices placed on the line. 

Lines. Halleyau A term sometimes 

applied to the isogonal lines. 

The isogonal lines are sometimes called the 
Halleyau lines, from Halley, who published the 
first chart of such lines in the ) ear 1701. 

Lines, Isoharic Lines connecting 

places on the earth's surface which simulta- 
neously have the same barometric pressure. 

The isobaric lines are sometimes called isobars. 

Lines, Isoclinic Lines connecting 

places that have the same angle of magnetic 
dip or inclination. (See Dip, Magnetic.) 

Lines, Isodynamic Lines connect- 
ing places which have the same total mag- 
netic intensity. 

The magnetic intensity of a place is determined 
by the number of oscillations that a small mag- 
netic needle, moved from its position ot rest in 
the magnetic meridian of any place, makes in a 
given time. Th s method is similar to ihat em- 
ployed for determining the intensity of gravity at 
any place. by observing the number ot oscillations 
that a pendulum of a given length makes in a 
given time at that place. If, for example, a mag- 
netic needle at one place makes 211 oscillations in 
ten minutes, and 245 in the same time at another 
place, then the relative intensities of magnetism 
at these places are as the squares ot those num- 
bers, or as 44,521 : 60,025, or as I : 1.348. 

Lines, Isogonal Lines connecting 

places that have the same magnetic declina- 
tion. (See Declination.) 

Lines, Isogenic —A term sometimes 

used for isogonal lines. ^See Lines, Zsogcnal.) 

Lines Isothermal Lines connect- 
ing points or places which have the same 
mean temperature. 

Lines, Kapp A term proposed by 

Mr. Gisbert Kapp for a unit of lines of mag- 
netic force. 

One Kapp line = 6,000 C. G. S. magnetic lines. 

Since there are 6.4514 square centimetres in a 

square inch, 1 Kapp line per square inch 

6,000 



6.45 1 4- 



= 930 C. G. S. lines per square cm. 



Lin.J 



3^2 



[Loc. 



The total number of Kapp lines passing through 
a magnet and air space is equal to the ampere 
turns divided by the total magnetic reluctance in 
the magnetic circuit. — (Urquhart.) 

Lines of Electric Displacement. — (See 
Displacement, Electric, Lines of) 

Lines of Electrostatic Force.— (See Force, 
Electrostatic, Lines of.) 

Lines of Force, Cutting (See Force, 

Lines of, Cutting.) 

Lines of Force, Direction of (See 

Force, Lines of, Direction of) 

Lines of Inductive Action.— (See Action, 
Inductive, Lines of) 

Lines of Magnetic Force. — (See Force, 
Magnetic, Lines of) 

Lines of Magnetic Force, Conducting 

Power for — (See Force, Magnetic, 

Lines of. Conducting Power for) 

Lines of Magnetic Induction. — (See In- 
duction, Magjietic, Lines of) 

Lines, Overhead A term applied 

to telegraph, telephone and electric light or 
power lines that run overhead, in contradis- 
tinction to similar lines placed underground. 

Lines, Vortex-Stream Lines ex- 
tending in the direction in which the particles 
of a fluid are moving. 

A vortex stream is supposed to be composed of 
a number of vortex-stream lines. 

Linked Magnetic and Electric Chain. — 

(See Chain, Linked Magnetic and Electric.) 

Links, Fuse — Strips or plates of 

fusible metal in the form of links, employed 
for safety fuses for incandescent or other 
circuits. 

Liquid, Bright Dipping A liquid 

used in electro-plating for dipping articles 
preparatory to electro-plating, so as to insure 
a bright plating deposit on them when after- 
wards subjected to the plating process. 

A bright dipping liquid is prepared by the ad- 
dition of I volume of common table salt to a 
mixture of ioo volumes each of sulphuric and 
nitric acids. For small objects or articles of 
copper, or other readily corroded metals, the 



above solution is diluted by the addition of one- 
eighth its volume of water. 

Liquid, Electropoion A battery 

liquid consisting of i pound of bichromate 
of potash dissolved in 10 pounds of water, to 
which i\ pounds of commercial sulphuric 
acid has been gradually added. 

This liquid is employed with the carbon-zinc 
cell or the bichromate of potash cell. 

Liquid, Exciting, of Voltaic Cell 

The electrolyte or liquid in a voltaic cell, 
which acts on the positive plate. 

Liquid Level Alarm. — (See Alann, Water 
or Liquid Level) 

Liquid Resistance Load. — (See Load, 
Liquid Resistance) 

Liquid, Stripping A liquid em- 
ployed to remove a coating of one metal 
from the surface of another, without affecting 
the other metal. 

The character of the stripping liquid used will 
depend on the kind of metal to be removed, and 
whether the stripping is to be accomplished by 
solution effected by chemical action, or by electro- 
lytic action. 

Liquid, Specific Resistance of 

(See Resistance, Specific, of Liquid) 

Liquor, Spent Any liquor, such as 

that in the acid or other baths used in electro- 
plating, that has become weakened by use. 

Listening Cam. — (See Cam, Listening) 

Load, Liquid Resistance An artu 

ficial load for a dynamo-electric machine, 
consisting of a mass of liquid interposed be- 
tween electrodes. 

A liquid is generally rendered better conduct- 
ing by the addition of a small quantity of soluble 
salt, such, for example, as sulphate of soda. 

Local Action of Dynamo-Electric Ma- 
chine. — (See Action, Local, of Dynamo- 
Electric Machine) 

Local Action of Voltaic Cell.— (See Ac^ 
tion, Local, of Voltaic Cell) 

Local Battery. — (See Battery, Local) 

Local Battery Circuit. — (See Circuity 
Local-Battery) 



Xoc] 



323 



[Loo. 



Local Currents. — (See Currents, Local.) 

Local Faradization. — (See Faradization, 
JLocal.) 

Local Galvanization. — (See Galvaniza- 
tion, Local.) 

Localization of Faults. — (See Faults, 
Localization of.) 

Lock, Electric A lock that is au- 
tomatically unlocked by the aid of electricity. 

The electric lock is so arranged that the action 
of a push button at a distance unlocks the door. 
A speaking tube communicates with the house, 
,and the pressing of a push button on any floor of 
the house unlocks the door. The mere shutting 
,of the door locks it. 

A form of electric lock is shown in Fig. 347. 




Fig. 347. Electric Lock. 

Locomotive, Electric 



— A railway 
^engine whose motive power is electricity. 
(See Railroads, Electric?) 

Locomotive Head Light, Electric 

(See Head Light, Locomotive?) 

Lodestone. — A name formerly applied to 
an ore of iron (magnetic iron ore), that natu- 
rally possesses the power of attracting pieces 
of iron to it. 

Lodestone, or magnetic iron ore, must be re- 
garded as a magnetizable substance that has be- 
come permanently magnetic from its situation in 
the earth's magnetic field. Such beds of ore 
concentrate the lines of the earth's magnetic field 
■on them, and thus become magnetic. 



Lodge's Standard Voltaic Cell. —(See 
Cell, Voltaic, Standard, Lodge s.) 

Log", Electric An electric device 

for measuring the speed of a vessel. 

A log, operated by the rotation of a wheel, is 
caused to register the number of its rotations by a 
step-by-step recording apparatus operated by 
breaks in the circuit, made during the rotation 
of the wheel, at any given number of turns, say 
100, or some other convenient multiple. Such a 
log may be kept constantly in the water, and ob- 
served when required, or it can be caused to 
make a permanent record of its actual speed at 
any time during the entire run. 

Logarithm. — The exponent of the power 
to which it is necessary to raise a fixed num- 
ber, in order to produce a given number. 

A table of logarithms enables the operations of 
multiplication, division, the raising of powers, 
and the extraction of roots, to be readily per- 
formed by simple addition, subtraction, multi- 
plication or division, respectively. When thor- 
oughly understood, logarithms greatly reduce the 
labor of mathematical calculations. For the man- 
ner in which they are used, the student is referred 
to any standard work on mathematics. 

Logarithmic Curve. — (See Curve, Loga- 
rithmic?) 

Long-Coil Magnet. — (See Magnet, Long- 
Coil?! 

Long-Core Electro-Magnet. — (See Mag- 
net, Electro, Long-Core.) 

Long-Shunt Compound- Wound Dynamo- 
Electric Machine. — (See Machine, Dyna- 
mo-Electric, Compound- Wound, L o 11 g- 
Shunt.) 

Longitude, Electric Determination of 

The determination of the longitude of 

a place, by differences in time between it and 
a place on the prime meridian, as simultane- 
ously determined telegraphically. 

In determinations of this character allowance 
must hi made for the retarding effects of long 
telegraphic lines, or cables. 

Loom, Electric A device by means 

of which Jacquard cards in the ordinary loom 
are replaced by a simple perforated metal 
plate, the perforations in which correspond 
to those in the Jacquard card. 



Loo.] 



324 



[Lux, 



The necessary movements are effected by 
means of electro-magnets. 

Loop Break. — A device for introducing a 
loop in a break made at any part of a circuit. 

The rigidity of the line wire, between the points 
of attachment of the loop introduced, is main- 
tained by means of some inflexible non-conducting 
material inserted in the break. 

Loop Circuit. — (See Circuit, Loop) 

Loop, Drip An inclined loop placed 

where the outside conductors enter 3. build- 
ing. 

The inclination is upwards towards the point 
of entrance to the building. This device of 
a drip loop is adopted for the purpose of prevent- 
ing the rain water from flowing along the inclined 
wire into the building. This is effected by making 
the wire incline from the building, thus throwing 
the drainage from the building. 

Loop, Electric A portion of a main 

circuit consisting of a wire going out from 
one side of a break in the main circuit and 
returning to the other side of the break. 

Loops are employed for the purpose of con- 
necting a branch telegraph office with the main 
line; for placing one or more electric arc lamps 
on the main line circuit; for connecting a mes- 
senger call ox telephone circuit with a mainline; 
and for numerous similar purposes. 

Loops of Force. — (See Force, Loops of) 

Loops of Mutual Induction. — (See Induc- 
tion, Mutual, Loops of) 

Low-Resistance Magnet. — (See Magnet, 
Low-Resistance.) 

Low-Tension Electric Fuse.— (See Fuse, 
Electric, Low- Tension.) 

Loxodrograph. — An apparatus for electri- 
cally recording on paper the actual course of 
a ship by the combined action of magnetism 
and photography. 

Luces. — Plural of lux. (See Lux) 

Luminescence.— A limited power of emit- 
ting light, possessed by certain bodies which 
have previously acquired potential energy by 
exposure to light or radiant energy. 

The term luminescence was proposed by E. 
Wiedemann to cover the case of the emission of 



light under circumstances differing from the emis- 
sion or radiation of light by incandescence. Lu- 
minescence applies to the case of a radiation, 
generally selective in character, that is apparently 
due to effects allied to, or the same as, those of 
fluorescence and phosphorescence. For example, 
magnesium oxide or zinc oxide, when heated 
above a certain critical temperature, radiates far 
more light than equally hot carbon. 

The spectrum of such luminescent light is espe- 
cially rich in certain wave lengths. The ability 
of the substance to continue to furnish this extra 
light is, however, limited. After a comparatively 
short time, the additional light, or selective radia- 
tion, disappears. The luminescent light is appa- 
rently due to molecular potential energy stored in 
the substance during its exposure to light. Lumi- 
nescence may be developed in bodies in the fol- 
lowing manner, viz. : 

(I.) By heat. 

(2.) By chemical action. 

(3.) By friction. 

(4. ) By exposure to the sun, or by actual impact 
of light waves. 

(5.) By electricity. 

(6.) By vital forces, as in the fire fly, or the 
glow worm. 

Luminescence, Rejuvenation of 

Reimparting by exposure to light, or any other 
suitable means, the power of luminescence to 
a substance after it has lost this power. 

Luminous Absorption. — (See Absorption^ 
Luminous) 

Lunar Inequality of Earth's Magnetic 
Variation or Inclination. — (See Inequality, 
Lunar, of Earth's Magnetic Variation or 
Inclination) 

Lunar Inequality of Earth's Magnetism.. 

— (See Inequality, Lunar, of Earth 's Mag- 
netism) 

Lux.— A name proposed by Preece for the: 
unit of intensity of illumination. 

The illumination given by a standard 
candle at the distance of 12.7 inches. 

The illumination given by 1 carcel at the 
distance of 1 metre. 

The illumination given by a lamp of 1 0,00a 
candles at 105.8 feet. (See Illumination,. 
Unit of) 



MJ 



325 



[Mac. 



M 



M. — A contraction sometimes used to ex- 
press a gaseous pressure of the .000001 of 
an atmosphere. 

1,000,000 M. equals 760 mm. of mercury or I 
atmosphere of pressure. 

A vessel containing air, which has been ex- 
hausted to the .000001 of its pressure at 760 
mm., or one atmosphere, has a pressure or ten- 
sion of 1 M. 

This contraction is used by Crookes in his re- 
searches on the properties of radiant matter. (See 
Matter, Radiant, or Ultra Gaseous. ) 

f.i. — A contraction used in mathematical 
writings for magnetic permeability, or the 
specific conductibility of any substance for 
lines of magnetic force. 

mm. — A contraction for millimetre. (See 
Weights, French System of.) 

M. P. H. — A contraction sometimes used in 
railroad work to indicate miles per hour. 

Machine, Armstrong's Hydro-Electric 

A machine for the development of 

electricity by the friction of a jet of steam 
passing over a water surface. 

Steam generated in a suitably insulated boiler, 




Fig. 348. Armstrong's Hydro- Electric Machine. 

Fig. 348, is allowed to escape through a tortuous 
nozzle, from a series of apertures opposite a 
pointed comb, attached to an insulated conductor. 



The cooling of the steam during its passage 
through a flat box, termed the coolin » box, con- 
nected with the nozzles, cau-es a partial. condensa- 
tion, so that the box always contains a small 
quantity of water. 

The friction of the drops of water against the 
orifice, and, possibly, their friction against the 
water surface itself, are the cause of the electricity 
produced. 

A conductor connected with the pointed comb 
furnishes positive electricity. The boiler fur- 
nishes negative electricity. The hydro-electric 
machine is not a very economical source of elec- 
tricity, and is only employed for experimental 
purposes. It was discovered accidentally through 
a shock given to an engineer, who placed his 
hand in a jet of steam escaping from a leaking 
boiler he was endeavoring to mend. The causes 
were first studied by Sir Wm. Armstrong, who, 
in 1840, devised the apparatus just dcscri .ed. 

Machine, Dynamo-Electric — A 

machine for the conversion of mechanical 
energy into electrical energy, by means of 
magneto-electric induction. 

The term is also applied to a machine by 
means of which electrical energy is converted 
into mechanical energy by means of magneto- 
electric induction. Machines of the latter class are 
generally called motors, those of the former, 
generators. 

Prof. S. P. Thompson defines a dynamo-eh c- 
tric machine as follows, viz.: "A machine for 
converting energy in the form of mechanical 
power into energy in the form of electric currents, 
or vice versa, by the operation of setting con- 
ductors (usually in the form of coils of copper 
wire) to rotate in a magnetic field, or by vary- 
ing a magnetic field in the presence of conduc- 
tors." 

The term dynamo was first applied to such 
machines, because in the form in which this 
machine first appeared, viz.: the series-wound 
machine, it was self- exciting, or required no ex- 
citement other than what it received by the rota- 
tion of its armature in the field of its magnets, 
or, indeed, in the field of the earth. (See Machine, 
Dyna?no-Electric, Reaction Principle of. ) 

A dynamo-electric generator, or a dyna??w-elec- 



Mac] 



326 



[Mac. 



•trie machine proper, consists of the following 
parts, viz.: 

(i.) The revolving portion, usually the arma- 
ture, in which the electromotive force is developed, 
which produces the current. 

It must be borne in mind that it is not current, 
but difference of electric potential, ox electromotive 
force, that is developed by any electric source 
from which a current is obtained. For ease of 
reference, however, we will speak of an electric 
current as being generated by the armature, or by 
the source. No ambiguity will be introduced if 
the student bears the above in mind. 

(2.) The fiela \ magnets, which produce the field 
in which the armature revolves. 

(3. ) hi pole pieces, or free terminals of the field 
magnets. 

(4.) The commutator, by which the currents de- 
veloped in the armature are caused to flow in 
one and the same direction. In alternating 
machines, and in some continuous current dynamos 
this part is called the collector, and does not rec- 
tify the currents. 

(5.) The collecting brushes, that rest on the 
-commutator cylinder and take off the current 
generated in the armature. 

Machine, Dynamo-Electric, Alternating- 
Current A dynamo-electric machine 

in which alternating currents are produced. 

The field magnets may be either permanent 
magnets or electro-magnets. When electro-mag- 
nets are used, their coils may be separately ex- 
cited by another machine whose current is con- 
tinuous; or, they may be excited by the commuted 
current of a separate coil on the armature; or, they 
may be partly excited by commuted currents and 
partly by commuted currents from a transformer, 
placed in the main circuit of the dynamo. 

Machine, Dynamo-Electric, Armature of 

(See Armature, Dynamo-Electric 

Machine) 

Machine, Dynamo-Electric, Bed-Piece of 

■ The frame or base on which a dynamo 

is supported. 

The bed-piece is sometimes called the dynamo 
frame or base. 

Machine, Dynamo-Electric, Bi-Polar 

— A dynamo-electric machine, the armature 
of which rotates in a field formed by two 
magnet poles, as distinguished from a ma- 



chine the armature of which rotates in a field 
formed by more than two magnet poles. 

A dynamo-electric machine whose armature 
rotates in the field formed by more than two 
poles is called a multi-polar machine. (See Ma- 
chine, Dyna7?io-Electric, Multi-Polar.) 

Machine, Dynamo-Electric, Carcass of 

A term sometimes used in place of 

the field magnet frame of a dynamo-electric 
machine. (See Machine, Dynamo-Electric, 
Frame of.) 

The term, field magnet frame, would appear 
to be the preferable term. The term, however, 
is used in France, and is derived from the 
French word for skeleton. 

Machine, Dynamo-Electric, Closed-Coil 

A dynamo-electric machine, the 

armature coils of which are grouped in sec- 
tions, communicating with successive bars of 
a collector, so as to be connected continu- 
ously together in a closed circuit. 

The Gramme dynamo and most continuous- 
current dynamos are closed-coil dynamos. 

Machine, Dynamo-Electric, Closed-Coil 

Disc A closed-coil dynamo-electric 

machine, the armature core of which is disc- 
shaped. 

Machine, Dynamo-Electric, Closed-Coil 

Drum A closed-coil dynamo-electric 

machine, the armature core of which is 
drum-shaped. 

Machine, Dynamo-Electric, Closed-Coil 

Ring" A closed-coil dynamo-electric 

machine, the armature core of which is ring- 
shaped. 

Machine, Dynamo-Electric, Collectors 

(See Collectors of Dynamo-Electric 

Machines.) 

Machine, Dynamo-Electric, Compound 
Winding of ■ — (See Winding, Com- 
pound, of Dyna?no-Electric Machine) 

Machine, Dynamo-Electric, Compound- 
Wound Machines whose field mag- 
nets are excited by more than one circuit of 
coils, or by more than a single electric 
source. 

The object of compound winding is to make 



Mac] 



327 



[Mac. 



the dynamo self-regulating under changes in its 
working load. A shunt-wound dynamo renders 
both series and multiple circuits approximately 
constant as regards their working. Multiple cir- 
cuits, however, require great constancy of poten- 
tial, and for this purpose the compounding of the 
dynamos is necessary. 

In the compound dynamo, the shunt coils are 
superposed on the series coils, or are used in con- 
nection with them. The shunt coils consist of a 
much greater number of convolutions of fine wire 
than the series coils, which are of coarse wire. 

Separate excitation is sometimes compounded 
either with series or with shunt field magnet 
•coils. 

Compound dynamos are of two classes, viz.: 

(i.) Those designed to produce a constant 
potential, and 

(2. ) Those designed to produce a constant cur- 
rent. 

For Constant Potential : 

In the long-shunt compound-wound dynamo, 
the terminals of the shunt coil are connected with 
the binding posts of the machine. As the cur- 
rent leaves the armature it has two paths to take : 
one, the thick series coils, to the external circuit, 
and the other the finer and longer shunt coils. 
The resistance of the shunt coils is greater than 
that of the armature. Current variations in the 
armature will, therefore, produce no appreciable 
effect on the magnetizing power of the shunt, 
which acts as a nearly uniform exciter of the field. 

In a shunt-wound dynamo connected to a 
multiple circuit, the introduction of an additional 
number of receptive devices into the circuit re- 
quires more current, and this would tend to cause 
a slight drop in the potential. The object of the 
series coils is to prevent this drop. The series 
coils, therefore, act as compensators. If the 
coils are too powerful the compensation will 
have the effect of increasing the potential. 

The combination of a series and separately ex- 
cited machine is shown in Fig. 351. The field is 
in series with the armature, but has also an ad- 
ditional and separate excitation. 

The combination of a series and shunt machine 
insures the excitation of the field both by the 
main and by the shunted current. Such a com- 
bination is shown in Fig. 353. 

For Constant Current : 

The combination of shunt and separately ex- 
cited machines is shown in Fig. 356. In this 
machine the field is excited by means of a shunt 



to the external circuit, and by a current produced 
by a separate source. 

The combination of a series and magneto ma- 
chine is shown in Fig. 352. This, also, is 
designed to give a constant current. 

Machine, Dynamo-Electric, Compound- 
Wound, Long-Shunt A compound- 
wound dynamo- electric machine, in which 
the shunt-field magnet coils form a shunt to 
the binding posts of the machine. 

In the short-shunt compound-wound dynamo - 
electric machine, the ends of the shunt coil are 
connected to the brushes of the machine. 

Machine, Dynamo-Electric, Compound- 
Wound, Short-Shunt A compound- 
wound dynamo-electric machine in which the 
shunt-field magnet coils form a shunt to the 
armature only, as distinguished from the 
armature and series coils combined. 

In the short-shunt dynamo-electric machine, 
the ends of the shunt coil are connected to the 
brushes of the machine, and not to the binding 
posts of the machine, or to the external circuit, as 
in the long-shunt machine. 

Machine, Dynamo-Electric, Continuous- 
Current A dynamo-electric machine, 

the current of which is commuted so as to 
flow in one and the same direction, as dis- 
tinguished from an alternating dynamo. 

Machine, Dynamo-Electric, Double-Mag- 
net A term sometimes applied to a 

dynamo-electric machine, the field magnets 
of which have two consequent poles. 

Machine, Dynamo-Electric, Economic 
Co-efficient of ■ — A name formerly ap- 
plied to the efficiency of a dynamo-electric 
machine. (See Machi?ie, Dynamo-Electric, 
Efficiency of.) 

Machine, Dynamo-Electric, Efficiency 

of The ratio between the electric 

energy or the electrical horse-power produced 
by a dynamo, and the mechanical energy or 
horse-power expended in driving the dynamo. 

The Efficiency may be the Commercial Effi- 
ciency, which is the useful or available energy in 
the external circuit divided by the total mechan- 
ical energy ; or it maybe the Electrical Efficiency, 
which is the available electric energy divided by 
the total electric energy. 



Mac. 



328 



[Mac 



The Efficiency of Conversion is the total elec- 
trical energy developed, divided by the total 
mechanical energy applied. 

If M, equals the mechanical energy, 

W, the useful or available electrical energy, 

and 
w, the electrical energy absorbed by the ma- 
chine, and 
m, the Stray Power, or the power lost in 
friction, eddy currents, air friction, etc. 
Then, since 
M = W + w -f m, 
Commercial Efficiency . . = = 



Machine, Dynamo-Electric, Open-Coil 

A dynamo-electric machine, the 

armature coils of which, though connected to 



Electrical Efficiency = 

Efficiency of Conversion 



M W 
W 



W + w 
_W -j- w_ W 4- w 



M W-f- w -j- m 
Machine, Dynamo-Electric, Flashing 1 of 

A name given to long flashing sparks 

at the commutator, due to the short cir- 
cuiting of the external circuit at the com- 
mutator, by arcing over the successive com- 
mutator insulating strips. 

Machine, Dynamo-Electric, Frame of 
The bed-piece that supports a dyna- 
mo-electric machine. 

The frame is sometimes called the dynamo bed- 
piece. 

The word frame is sometimes applied to the 
field magnet cores and yokes. 

Machine, Dynamo-Electric, Local Action 

of (See Action, Local, of Dynamo- 
Electric Machined) 

Machine, Dynamo-Electric, Mouse-Mill, 
Sir Wm. Thomson's A dynamo- 
electric machine designed by Sir Wm. 
Thomson, named from the resemblance of 
its armature to a mouse mill. 

The armature conductor of this dynamo con- 
sists of parallel bars of copper, arranged on a 
hollow cylinder, like the bars on a mouse mill. 

Machine, Dynamo-Electric, Multipolar 

— A dynamo-electric machine, the 

armature of which revolves in a field formed 
by more than a single pair of poles. 

This form is usually adopted for large machines 
as being more economical. 

Fig. 349 shows a multipolar dynamo with four 
poles. 




Fig, S49- Multipolar Dynamo wi.k Four Poles. 

the successive bars of the commutator, are not 
connected continuously in a closed circuit. 

The Brush and the Thomson-Houston arc dy- 
namos are open-coil machines. 

Machine, Dynamo-Electric, Open-Coil 

Disc An open-coil dynamo-electric 

machine, the armature of which is disc- 
shaped. 

Machine, Dynamo-Electric, Open-Coil 

Drum An open-coil dynamo-electric 

machine, the armature core of which is drum- 
shaped. 

Machine, Dynamo-Electric, Open-Coil 

Ring" — An open-coil dynamo-electric 

machine, the armature core of which is ring- 
shaped. 

Machine, Dynamo-Electric, Output of 

The electric power of the current gen- 
erated by a dynamo-electric machine ex- 
pressed in volt-amperes, watts or kilo-watts. 
S. P. Thompson suggests that dynamo- electric 
machines be rated as to their practical safe ca- 
pacity in units of output of 1,000 watts, or one 
kilo-watt. According to this, an 8-unit machine 
might give, say, ioo amperes at a difference of 
potential of 8o volts, or 2,000 amperes at a differ- 
ence of potential of 4 volts. Such a unit would be 
far more expressive than the usual method ot rat- 
ing a machine as having a capacity of such and 
such a number of lights. 

Machine, Dynamo-Electric, Reaction 
Principle of — The mutual interaction 



Mac] 



329 



[Mac 



between the current generated in the armature 
coils of a dynamo-electric machine and the 
field of the machine, each strengthening the 
other until the full working current, which 
the machine is capable of developing, is 
produced. 

When the armature of a series or shunt dynamo 
commences to rotate, the differences of potential 
generated in its coils are very small, since the 
field of the magnet is weak, being merely the 
residual magnetism. The current so produced 
in the armature, circulating through the field 
magnet coils, increases the intensity of the mag- 
netic field of the machine, and this, reacting on 
the armature, results in a more powerful current 
through it. This current again increases the 
strength of the magnetic field of the machine, 
which again reacts to increase the current 
strength in the armature coils, and this continues 
until the machine is producing its full output. 

A dynamo-electric machine very rapidly 
'-'■builds uj>," or reaches its maximum current 
after starting. The reaction principle was dis- 
covered by Soren Hjorth, of Copenhagen. 

Machine, Dynamo-Electric, Reversibility 

of The ability of a dynamo to act as 




D D D D 

Fig- 35°' Separately Excited Dynamo 

a motor when traversed by an electric cur- 
rent. (See Motor, Electric.) 

Machine, Dynamo-Electric, Separate 

Coil A dynamo- electric machine in 

which the field magnets are excited by means 



of coils on the armature, separate and dis- 
tinct from those which furnish current to the 
external circuit. 

Machine, Dynamo-Electric, Separately 

Excited A dynamo-electric machine 

in which the field magnet coils have no con- 
nection with the armature coils, but receive 
their current from a separate machine or 
source. 

A separately excited dynamo -electric machine 
is shown in Fig. 350. 

Separate excitation for constant current ma- 
chines has not come into any extended use in the 
United States. 

Machine, Dynamo-Electric, Series and 
Magneto — A compound-wound dy- 
namo-electric machine in which the arma- 
ture circuit of a magneto-electric machine is 
connected in series with the armature and 
field magnet circuits of a series dynamo. 

The circuit connections of a series and magneto 
dynamo are shown in Fig. 351. 




R R R R 
^.11, av^ji^. &'^/, m^ j&k, i^- 

Fig 3 Si- Series and Magneto Dynamo. 

Machine, Dynamo-Electric, Series and 
Separately Excited — A compound- 
wound dynamo-electric machine in which 
there are two separate circuits on the field 
magnet cores, one of which is connected in 
series with the field magnets and the exter- 
nal circuit, and the other with some source 
by which it is separately excited. 



Mac] 



330 



[Mac. 



A series and separately excited compound - 
Wound dynamo-electric machine is shown in 
Fig. 352. 







Fig. 352. Series and Separately Excited Dynamo. 

This machine is employed for maintaining a 
constant potential at its terminals. 

Machine, Dynaino-Electric, Series and 
Shunt Wound — A compound-wound 




Fig. 353. Series and Shunt- Wound Dynamo. 

dynamo-electric machine in which the field 
magnets are wound with two separate coils, 
one of which is in series with the armature 
and the external circuit, and the other in 
shunt with the armature. 



This is usually called a compound- wound ma- 
chine. (See Machine, Dynamo -Electric, Com- 
pound- Wound.) 

A compound-wound series and shunt dynamo- 
electric machine is shown in Fig. 353. This ma- 
chine is designed to maintain constant potential 
at its terminals. 

There are two varieties of series and shunt - 
wound dynamos, viz.: 

(1.) Long-shunt compound-wound dynamo. 

(2.) Short-shunt compound- wound dynamo. 

(See Machine, Dynamo-Electric, Compound- 
Wound, Long- Shunt. Machine, Dynamo-Electric, 
Compound- Wound, Short -Shunt.) 

Machine, Dynamo-Electric, Series- Wound 

A dynamo-electric machine, in which 

the field circuit and the external circuit are 




D D D D 

Fig. 334. Series Dynamo. 

connected in series with the armature circuit,, 
so that the entire armature current must pass 
through the field coils. 

A series dynamo -electric machine is shown in 
Fig. 354- Here the armature circuit, the field 
circuit and the external circuit are all connected 
in series. 

Since in a series-wound dynamo the armature 
coils, the field and the external series circuit are in 
series, any increase in the re -istance of the external 
circuit will decrease the electromotive force from 
the decrease in the magnetizing currents. A de- 
crease in the resistance of the external circuit will, 
in a like manner, increase ths electromotive force 
from the increase in the magnetizing current. 



Mac! 



331 



[Mac. 



The use of a regulator avoids these changes in 
the electromotive force. 




Fig. 355. Series Dynamo. 

The dynamo shown in Fig. 355 is series con- 
nected. The armature is ring-shaped. The 
armature core consists of a ring made of so r t iron 
wire. The field is bi-polar, and is obtained by 
the use of four magnet coils and two consequent 
poles. 

Machine, Dynamo-Electric, Shunt and 
Separately Excited A compound- 
wound dynamo-electric machine, in which 




R R R R 

Fig. 35 b. Shunt and Separately Excited Dynamo. 

the field is excited both by means of a shunt 
to the armature circuit, and by a current pro- 
duced by a separate source. 

A shunt and separately excited compound- 



wound dynamo-electric machine is shown in Fig. 
356. This machine maintains a constant current 
in its circuit, notwithstanding changes in its ex- 
ternal circuit. 

Machine, Dynamo-Electric, Shunt- Wound 

A dynamo-electric machine in which 

the field magnet coils are placed in a shunt 
to the armature circuit, so that only a 
portion of the current generated passes 
through the field magnet coils, but all the 
difference of potential of the armature acts at 
the terminals of the field circuit. 

A shunt dynamo-electric machine is shown in 
Fig. 357- 




Fig. 357- 



D D D 
Shunt Dynamo. 



In a shunt dynamo electric machine, an in- 
crease in the resistance of the external circuit in- 
creases the electromotive force, and a decrease in 
the resistance of the external circuit decreases the 
electromotive force. This is just the reverse of 
the series-wound dynamo. 

In a shunt-wound dynamo a continuous balanc- 
ing of the current occurs. The current dividing 
at the brushes between the field and the external 
circuit in the inverse proportion to the resistance 
of these circuits, if the resistance of the external 
circuit becomes greater, a proportionately greater 
current passes through the field magnets, and so 
causes the electromotive force to become greater. 
If, on the contrary, the resistance cf the external 
circuit decreases, less current passes through the 
field, and the electromotive force is proportion, 
ately decreased. 



Mac. 



332 



[Hac. 



In a shunt-wound dynamo the resistance of the 
Shunt should be at least four hundred times that 
of the armature. It is sometimes as much as one 
thousand times as great. — {Urquhart.) 

To obtain complete regulation of the machine 
some form of compounding is neces-ary. (See 
Machine, Dynamo-Electric, Compound- Wound. ) 

Machine, Dynamo-Electric, Single-Mag- 
net A dynamo-electric machine, in 

which the field magnet poles are obtained by 
means of a single coil of insulated wire, in- 
stead of by more than a single coil. 

Machine, Dynamo-Electric, Sparking- of 

■ — An irregular and injurious operation 

of a dynamo-electric machine, attended with 
sparks at the collecting brushes. 

Sparking consists in the formation of small arcs 
under the collecting brushes. One cause of 
sparking is to be found in the brushes leaving one 
commutator strip before making connection with 
the next strip. 

Sparking from this cause may be avoided by so 
placing the brushes as to cause them to bridge 
over the space between two consecutive bars, thus 
permitting them to touch one bar before leaving 
the other. Two brushes, electrically connected, 
are sometimes employed for this purpose, or the 
slots between contiguous bars are slightly inclined 
to the axis of rotation. 

Sparking causes a burning of the commutator 
strips, and an irregular consumption of the 
brushes, both of which produce further irregulari- 
ties by the wear of the brushes against the com- 
mutator bars. 

At the moment the brush touches two contigu- 
ous commutator bars, it short circuits the coil 
terminating at those bars. On the breaking of 
this closed circuit, a spark appears under the 
brushes. This spark is often considerable, since 
from the comparatively small resistance of the 
coil, it is apt, when short circuited, to produce a 
heavy current if not exactly at the neutral point. 

Another cause of sparking is to be found in the 
seif-induction of the armature coils. The extra 
current on breaking forms an injurious spark un- 
der the brushes. This spark may be considerable, 
since the current produced in the coil on mo- 
mentarily short circuiting it by the brushes sim- 
ultaneously touching the adjoining commutator 
segments may be large. 

Sparking occurs when the brushes are not set 



close to the neutral line. Since the principal 
cause for the change in the lead of the brushes is 
the magnetizing effect of the armature coils, it is 
preferable to make the number of windings of 
these as few as possible, and to obtain the neces- 
sary differences of potential by increasing the 
speed of rotation and the strength of the magnetic 
field of the machine. Short armature coils also 
lessen the sparking due to self-induction. 

Sparking at the brushes is also caused by the 
jumping of improperly supported or constructed 
brushes 

When the brushes are not set close to the neu- 
tral point, long flashing sparks are apt to occur. 

A lack of symmetry of winding of the arma- 
ture coils will necessarily be attended by injurious 
flashing, from the impossibility of properly ad- 
justing the brushes. 

Machine, Dynamo-Electric, Synchroniz- 
ing Adjusting the phases of two alter- 
nating current dynamos so as to permit their 
being coupled or joined in parallel. 

Machine, Dynamo-Electric, to Short Cir- 
cuit a To put a dynamo-electric ma- ' 

chine on a circuit of comparatively small 
electric resistance. 

Machine, Dynamo-Electric, Unit of Out- 
put of A unit for the electric power 

furnished by the current of a dynamo-electric 
machine. 

A unit of output equal to 1,000 watts or 
i kilowatt. 

A machine" furnishing a current of ioo amperes 
at a difference of potential of 80 volts, would 
have an output of 8,000 watts, and would, 
therefore, be rated as an 8-unit machine. 

Machine, Electric, Rubber of A 

cushion of leather covered with an electric 
amalgam, and employed to produce electricity 
by its friction against the plate or cylinder of 
a frictional electric machine. (See Ma- 
chine, Frict zonal Electric?) 

Machine, Electrostatic Induction 

A machine in which a small initial charge 
produces a greatly increased charge by its in- 
ductive action on a rapidly rotated disc of 
glass or other dielectric. 

An excellent type and example of such a ma- 
chine is found in the Iloltz machine, which c>>n- 



Mac J 



333 



[Hac. 



sists of the following parts, as shown in Fig. 358, 
viz.: 

(1.) A stationary glass plate A, fixed at its 
•edges to insulated supports. 

(2.) A movable plate B, capable of rapid rota- 
lion on a horizontal axis, by a driving pulley. 

A 




Fig. 338. Holtz Electric Machine. 

(3.) Armatures of varnished paper f, f ', placed 
-on opposite sides of the fixed plate at holes or 
windows P, P ', cut in the plate. The armatures 
are placed on the side of the fixed plate away from 
the moving plate, or on the back of the plate, so 
that the plate, on its rotation, moves towards 
tongues of paper attached to the middle of the 
arjnature. 

(4.) Metal combs placed in front of the movable 
disc opposite the armatures, and connected with 
the brass balls m, n, one of which is movable 
towards and from the other by means of a suitably 
supported insulating handle connected with it. 

A small initial charge is given to one of the 
armatures by holding a plate of electrified vul- 
canite against it, and rotating the machine while 
the balls m, n, are in contact. As soon as the ma- 
chine is charged the balls are gradually separated^ 
when a torrent of sparks will pass between them 
so long as the plate is rotated. 

When the balls are separated too far the sparks 
cease to pass. The balls must then be again 
brought into contact and gradually separated as 
before. 

The Holtz machine can be regarded as a re- 
volving electrophones provided with means for 
constantly discharging and recharging the upper 
metallic plate. (See Electrophorus.) 

The action of the machine is well described by 
S. P. Thompson in his " Elementary Lessons on 
Electricity and Magnetism,'"' as follows: 

' ' Suppose a small -4- charge to be imparted at 
the outset to the right armature f ; this charge acts 



inductively across the discs upon the metallic 
comb, repels electricity through it, and leaves the 
points negatively electrified. They discharge 
negatively electrified air upon the front surface of 
the movable disc; the repelled charge passes 
through the brass rods and balls, and is discharged 
through the left comb upon the front side of the 
movable disc. Here it acts inductively upon the 
paper armature, causing that part of it which is 
opposite itself to be negatively charged and re- 
pelling a -\- charge into its farthest part, viz., into 
the tongue, which being bluntly pointed, slowly 
discharges a -|- charge upon the back of the mov- 
able disc. If now the disc be turned round, 
this -|- charge on the back comes over from the left 
to the right side, in the direction indicated by the 
arrow, and, when it gets opposite the comb, in- 
creases the inductive effect of the already existing 
-(- charge on the armature, and therefore repels 
more electricity through the brass rods and knob 
into the left comb. Meantime the — charge, which 
we saw had been induced in the left armature, has 
in turn acted on the left comb, causing a -{- charge 
to be discharged by the points upon the front of 
the disc; and drawing elec:ncity through the 
brass rods and knobs, has made the right comb 
still more highly — , increasing the discharge of 
— ly electrified air upon the front of the disc, neu- 
tralizing the -f- charge which is being conveyed 
over from the left. These actions result in causing 
the top half of the moving disc to b^ — ly electri- 
fied. The charges on the front serve, as they are 
carried round, to neutralize the electricities let off 
by the points of the combs, while the charges on 
the back, induced respectively in the neighbor- 
hood of each of the armatures, serve, when the 
rotation of the disc conveys them round, to increase 
the inductive influence of the charge on the 
other armature." 

The student will be aided m following Prof. 
Thompson's explanation by the diagrammatic 
sketch, shown in Fig. 359. Here the rotating plate 
is shown for convenience in the f jrm of a cylinder. 
The armatures are shown on the back of the plate 
at f and f, opposite the brass collecting combs P' 
and P, with their discharging rods and balls a, a. 

The effect of the positive charge given to the 
right hand armature f, directly through the 
comb P , rods a, a, comb P, to left hand arma- 
ture f, is readily seen. The rotation of the plate 
being in the direction of the curved arrows, the 
charging of the front of the plate by convection 
streams from the combs, and the back of the plate 



Mac] 



334 



[Mac. 



from the points of the paper armatures, as well as 
the character of the charge, will be understood. 
There thus results, as is shown, a positive charge 
on both the front and back of the upper half of 




Fig. 35Q. Plate of Holt z Machine. 
the rotating plate, and a negative charge on both 
sides of its lower half. A reversal of polarity of 
the plate occurs at the line P a a P'. Sometimes 
the reversal does not occur, and the machine either 
loses its charge entirely, or in part. A conductor 
S S, furnished with points, is sometimes provided 
to lessen the chances of lack of reversal. 

Machine, Faradic A machine for 

producing faradic currents. 

There are two varieties of faradic machines, 
viz.: magneto faradic apparatus and simple in- 
duction apparatus. 

Machine, Frictional Electric A 

machine for the development of electricity by 
friction. 

A frictional electric machine consists of a plate 
or cylinder of glass A, Fig. 360, capable of rota- 
tion on a horizontal axis. 

A rubber formed of a chamois skin, covered 
with an amalgam of tin and mercury, is 
placed at B. By the rotation of the plate the 




Fig. J 60. Frictional Electric Machine. 

rubber becomes negatively and the glass posi- 
tively excited. An insulated conductor D, called 
the prime or positive conductor, provided with a 



comb of points, becomes positively charged by in- 
duction. The machine will develop electricity 
best if a conductor attached to the rubber is con- 
nected with the ground, as by a chain. 

Machine, Holtz A particular form 

of electrostatic induction machine. (See 
Machine, Electrostatic Induction^) 

Machine, Influence An electrical 

machine depending for its action on electro^ 
static induction. 

The Wimshurst and Holtz machines are influ- 
ence machines. (See Machine, Electrostatic In- 
duction. Machine, Wimshurst Electrical. Ma- 
chine, Holtz.) 

Machine, Influence, Wimshurst's Alter- 
nating- An electrostatic induction ma- 
chine by means of which a series of rapidly 
alternating charges are produced. 

Although such a machine furnishes a torrent of 
sparks between its terminals, yet it is unable to 
furnish a permanent charge to a Leyden jar 
or condenser, since its 
oscillatory discharges, 
continually undo at any 
small interval of time, 
what was done at the 
preceding interval, and 
thus leave the jar un- 
charged. 

Machine, Magneto 
Blasting — A 

magneto-electric ma- 
chine employed for 
generating the cur- 
rent used in electric pi, 
blasting. 




3 6 1 . Magneto- Electric 
Machine. 



Machine, Magneto-Electric A ma- 
chine in which there are no field magnet coils, 
the magnetic field of the machine being due 
to the action of permanent steel magnets. 

A dynamo in which currents are produced by 
the motion of armature coils past permanent mag- 
nets. (See Machine, Dynamo -Electric.) 

A magneto-electric machine is shown in Fig. 
361. 

Another form of magneto-electric machine is 
shown in Fig. 362. 

This latter form of machine is known as a hand 
generator, in contradistinction to one driven by 
power and called a power generator. 



Mac] 



335 



[Mac. 



The field is obtained by means of a number of 
separate permanent magnets so combined as to 




Fig. 362. Magneto-Electric Mach me. 

act as a single magnet. The armature is rotated 
by hand. 

Machine, Mouse-Mill A form of 

convection induction machine, invented by 
Sir William Thomson to act as the replen- 
isher of his electrometer. (See Machine, 
Electrostatic Induction?) 

Machine, Rheostatic A machine 

devised by Plante in which continuous static 
effects of considerable intensity are obtained 
by charging a number of condensers in mul- 
tiple-arc and discharging them in series. 

The condensers are charged by connecting 
them with a number of secondary or storage bat- 
teries. 

Machine Telegraphy. — (See Telegraphy, 
Machine?) 

Machine, Toppler-Holtz A modi- 
fied form of Holtz machine in which the 
initial charge of the armatures is obtained by 
the friction of metallic brushes against the 
armatures. 

Machine, Wimshurst Electrical 

A form of convection electric machine in- 
vented by Wimshurst. 

Like the Holtz machine, the Wimshurst ma- 
chine is a convection induction machine. It is, 
however, more efficient in action, and will prob- 
ably soon supersede the former machine. The 
Wimshurst machine consists of two shellac -var- 
nished glass plates that are rapidly rotated in op- 
posite directions. Thin metallic strips are placed 
on the outside of each of the plates, in the radial 
positions shown in Fig 363. These strips act 



both as inductors and carriers; the carriers of 
one plate acting as inductors to the other plate. 

Two curved brass rods, terminating in fine wire 
brushes that touch the plates, are placed as shown, 
one at the front of the plate, and one at the back, 
at right angles to each other. Pairs of conduct- 




Fig. 363. The Wimshurst Electrical Machine. 

ors, connected together, provided with collecting 
points, are placed diametrically opposite each 
other, as shown. Sliding conductors, terminated 
with metallic balls, are provided for discharging 
the conductors. Leyden jars, the inner coatings 
of which are connected with two discharging 
rods, and the outer coatings together, may be em- 
ployed in this as in the Holtz machine. 

The exact action of this machine is not thor- 
oughly understood. 

Machines, Dynamo-Electric, Varieties of 

Dynamo-electric machines may be 

divided into classes according to — 

(1.) The manner in which the magnetism of 
the field magnets is obtained. 

(2.) The character of their armatures. 

(3. ) The nature of the current obtained, whether 
continuous or alternating. 

(4.) The form of their field magnets. 

(5.) The nature of their magnetic fields. 

(6.) The manner in which the current of the 
field magnets, the armature and the external 
circuits are connected. 

Mack A term proposed by Mr. 

Oliver Heaviside for a unit of self-induction. 

The term Mack is derived from Maxwell. The 
unit of self induction has also been a secohm and 
a quadrant. 



MM.] 



336 



[Mag. 



The term Max would seem to be indicated. 
In the United States the unit of self-induction is 
called a Henry, after Prof. Joseph Henry. (See 
Henry, A.) 

Made Circuit. — (See Circuit, Made?) 

Magazine Fuse. — (See Fuse, Magazine.) 

Magne-Crystallic Action. — (See Action, 
Magne- Crystallic.) 

Magnet. — A body possessing the power 
of attracting the unlike pole of another mag- 
net or of repelling the like pole ; or of at- 
tracting readily magnetizable bodies like iron 
filings to either pole. 

A body possessing a magnetic field. (See 
Field, Magnetic?) 

The lines of force are assumed in passing 
through the magnetic field to come out at the north 
pole of the magnet and to go in at the south pole. 
All lines of force form closed magnetic circuits. If 
a magnetizable body is brought into a magnetic 
field, the lines of magnetic force are concentrated 
on it and pass through it. The body therefore be- 
comes magnetic. The intensity of the resulting 
magnetism depends on the number of lines of force 
that pass through the body, and the polarity on 
the direction in which they pass through it. 

A magnetized bar cannot be regarded as a 
source of energy in itself. Energy must be ex- 
pended to magnetize the iron, and must also be 
expended to demagnetize it. 

Magnet, Anomalous — A magnet 

possessing more than two free poles. 

There is no such thing as a unipolar magnet. 



Fig. 364. Anomalous Magnet. 

All magnets have two poles. Sometimes, how- 
ever, several magnets are so grouped that there 
appear to be more than two poles in the same 
magnet. 




It is clear, however, that the central pole is in 
reality formed of two juxtaposed negative poles, 
and that ABC, actually consists of two magnets 
with two poles to each. 

The magnet A B C D, Fig. 365, which in like 
manner appears to possess four separate poles, in 
reality is formed of three magnets with two poles 
to each. 

Since unlike magnetic poles neutralize each 
other, it is clear that only similar poles can thus be 
placed together in order to produce additional 
magnet poles. 

S S 




Fig. 3 6 J. Anomalous Magnet. 

Thus, in Fig. 364, the magnet ABC, appears 
to possess three poles, two positive poles at A 
and C, and a central negative pole at B. 



S S 

Fig. 366. Anomalous Magnet . 

The six-pointed star shown in Fig. 366, is an 
anomalous magnet with apparently seven poles. 
The formation of the central N-pole, as is evident 
from an inspection of the drawing, is due to the 
six separate north poles, n, n, n, n, n, n, of the 
six separate magnets Sn, Sn, etc. Such a magnet 
would be formed by touching the star at the point 
N, with the S-pole of a sufficiently powerful 
magnet. 

The extra poles are sometimes called consequent 
Poles. Their presence may be shown by means of 
a compass needle, or by rolling the magnet in iron 
filings, which collect on the poles. 

Magnet, Artificial A magnet pro- 
duced by induction from another magnet, or 
from an electric current. 

Any magnet not found in nature is called an 
artificial magnet. 

Magnet, Axial A name sometimes 

given to a solenoid with an axial or straight 
coie. 

Magnet, Bell-Shaped A modifica- 
tion of a horseshoe magnet in which the ap- 
proached poles are semi-annular in shape, and 
form a split tube. 

Bell- shaped magnets are used in many galva- 



Mag.] 



337 



[Mag. 



nometers, because they can be readily dampened 
by surrounding them by a mass of copper. The 
needle in its motion produces currents that tend 
to oppose, and, therefore, to stop its motion. (See 
Laws, Lenz's.) 

Magnet, Cluh-Footed An electro- 
magnet whose core is in the form of a horse- 
shoe and is provided with a magnetizing coil 
on one pole only. 

Magnet Coil.— (See Coil, Magnet) 

Magnet, Compensating A magnet 

placed over a magnetic needle, generally over 
the magnetic needle of a galvanometer, for 
the purpose of varying the direction and in- 
tensity of the magnetic force of the earth on 
such needle. (See Galvanometer, Reflecting.) 

A magnet, called a compensating magnet, is 
sometimes placed on a ship, near the compass 
needle, for the purpose of neutralizing the local 
variations produced on the compass needle by the 
magnetism of the ship. 

Magnet, Compound A number of 

single magnets, placed par- 
allel and with their similar 
poles facing one another, 
as shown in Fig. 367. 

Compound magnets are 
stronger in proportion to their 
weight than single magnets. 

Magnet, Compound 
Horseshoe A horse- 
shoe magnet composed of 
several separate horseshoe 
magnets placed with their 
similar poles together. 

A compound horseshoe Fig. 3 6 7. 
magnet is shown in Fig. 368. 

A horseshoe magnet possesses greater portative 
power than a straight bar magnet of the same 
weight. (See Pozver, Portative.') 

(1.) Because its opposite poles are nearer to- 
gether; and 

(2.) Because the magnetic resistance of its 
circuit is less, the lines of magnetic force closing 
through the armature, and thus concentrating 
the magnetic attraction on the armature. 

Electro-magnets are generally made of the 
horseshoe shape. 

Magnet, Controlling — A name 




Compound 

Magnet. 




sometimes applied to the controller in the 
Thomson- Houston automatic system of cur- 
rent regulation. (See Controller) 

Generally any mag- 
net which controls = 
some particular ac- 
tion. 

Magnet, Cylindri- 
cal A magnet 

in the shape of a cyl- 
inder. 

A helix or solenoid 
through which a cur- 
rent of electricity is 
passing is, so far as ex- 
ternal space is con- 
cerned, the exact mag- 
netic equivalent of a 
cylindrical magnet. 

Magnet, Damping 

— Any magnet 

employed for the pur- Fig. 368. Compound Horse- 

pose of checking the shoe Magnet. 

velocity of motion of a moving body or mag- 
net. 

Damping magnets generally act by the resist- 
ance which they offer to the passage of a 
metallic disc, so moved as to cut the lines of force 
of their field. 

Magnet, Electro A magnet pro- 
duced by the passage of an electric current 
through a coil of insulated wire surrounding 
a core of magnetizable material. 

The magnetizing coil is called a helix or sole- 
noid. (See Magnetism, Ampere'' s Theory of .) 

Strictly speaking, the term electro-magnet is 
limited to the case of a magnet provided with a 
soft iron core, which enables it to rapidly acquire 
its magnetism on the passage of the magnetizing 
current, and as rapidly to lose its magnetism on 
the cessation of such current. 

An electric current passed around a bar of 
magnetizable material, in the manner and direc- 
tion shown in Fig. 369, will produce the polarity 
N and S, at its ends or extremities as marked. 

The directions of the currents required to pro- 
duce N and S, poles respectively are shown in 
Fig. 370. 

The cause of this difference of polarity will be 
readily understood from a study of the direction 



Mag.] 



338 



[Ma< 



of lines of magnetic force in the field produced 
by an electric current. 




Fig 3bq< Polarity of Ctirrent. 

The direction of this polarity may be predicted 
by the following modification of a rule by Ampere: 

Imagine yourself swimming in the wire in the 
direction of the current; if, then, your face is 




Fig. 370, North and South Magnet Poles. 

turned toward the bar that is being magnetized, 
its North seeking pole will be on your left. 

A 





Fig- 37 t Deflection of 
Magnetic Needle. 



Fig- 37 2. Deflection of 
Magnetic Needle. 



If, for example, the conductor A B, be traversed 
by a current in the direction from E, to A, as 
shown in Fig. 371, the north pole N, of the 
needle N S, placed under the conductor, is de- 
flected, as shown, to the left of the observer, who 
is supposed to be swimming in the current, facing 
the needle. If the current flow in the opposite 



direction, as from A, to B, as shown in Fig. 372, 
the N, pole of the needle is deflected as shown, 
but still to the left of the observer supposed to be 
swimming as before. 

In any electric circuit, the lines of magnetic 
force, produced by the passage of the current, form 
circles around the circuit in planes at right angles 
to the direction of the current, as shown in Fig. 
373. The direction of these lines of force is the 
same as that of the hands of a watch, if the cur- 
rent be supposed to flow away from the observer. 
(See Field, Magnetic, of an Electric Current.) 




Fig. 373. Direction of Lines of Force. 

Remembering now that the lines of force are 
supposed to corned at the north pole of a magnet, 
and to pass in at the south pole, it is evident that 
if the current flows in the direction shown in Fig. 




Fig. 374. Direction of Lines of Force. 

374, the lines of force will come out at the north 
pole and pass in at the south pole. 

Since in a right-handed helix the wire passes 
around the axis in the opposite direction to that 
in which it passes in a left-handed helix, it is 
evident that the helices shown in Fig. 375 at I, 
and 2, will produce opposite polarities at the 
points of entrance and exit by a current flowing 
in the direction of the arrows. 

If the current be sent through the right handed 
helix, shown at I, from b, to a, that is, from the 
left to the right in the figure, a south pole will be 
produced at b, and a north pole at a. If, how- 
ever, it be sent from a, to b, the polarity will be 
revers d. 

If the current be sent through the left handed 



JUag.j 



339 



Ltfag. 



helix, shown at 2, from a, to b, that is, from the left 
to the right in the figure, a north pole will be pro- 
duced at a, and a south pole at b. If, however, it 
be sent in the opposite direction, the polarity will 
be reversed. 

Therefore, in an electro-magnet, on the core 
of which several layers or thicknesses of wire are 
wound, in which the current flows through one 
layer, in, say a direction from right to left, the cur- 
rent must return through the next layer in the 
opposite direction, or from left to right. The 
polarities of the same extremities of the helices 
are, however, the same in all cases, since the 
layers are successively right and left handed 
to the current. The winding shown at 3, pro- 
duces consequent poles. 

The following laws express the more important 
principles concerning electro-magnets: 

(1.) The magnetic intensity (strength) of an 
electro-magnet is nearly proportional to the 
strength of the magnetizing current, provided the 
core is not saturated. 

(2.) The magnetic strength is proportional to 
the number of turns of wire in the magnetizing 
coil; that is, to the number of ampere turns. (See 
Turns, Ampere.) 

(3.) The magnetic strength is independent of 
the thickness or material of the conducting wires. 

These laws may be embraced in the more gen- 
eral statement that the strength of an electro- 




F*g- 37 S 



Right- Handed, Left- Handed and Anomalous 
Helices. 



magnet, the size of the magnet being the same, 
is proportional to the number of its ampere turns. 
(S^e Turjis, Ampere. ) 

A short interval of time is required for a cur- 
rent to thoroughly magnetize a powerful electro- 
magnet. 

A few moments are also required for a power- 
ful magnet to thoroughly lose its magnetism. At 
the same time electro magnets are capable of 
acquiring or losing their magnetism with very 
great rapidity. It is in fact, 0:1 this ability pos- 
sessed to so remarkable a degree 1 y soft iron, that 



the value of an electro-magnet tor many purposes 
depends. (See Lag, Magnetic.') 

A difference exists between the action of a mag- 
netized disc and a hollow coil of wire through 
which a current of electricity is passing. So 
far as the space outside either is concerned, the 
action is the same, but the coil is penetrable on 
the inside and the disc is not, and for the inside ot 
the space, therefore, there is a difference in the ac- 
tion. 

Mag-net, Electro, Bar An electro- 
magnet, the core of which is in the form of a 
straight bar or rod. 

Mag-net, Electro, Cylindrical An 

electro-magnet, the core of which consists of 
a hollow cylinder provided with a slot extend- 
ing parallel to its axis. 

The gap in the cylinder suffices for the placing 
of the magnetizing coils, and forms the poles. 
This form of electro-magnet was devised by 
Joule. Its construction will be understood from 
an inspection of Fig. 376 




J 7 6. Cylindrical Electro-Mag net. 



Mag-net, Electro, Horseshoe — An 

electro-magnet, the core of which is in the 
shape of a horseshoe or U. 

Mag-net, Electro, Hug-lies' — An 

electro-magnet in which a U-shaped per- 
manent magnet is provided with pole pieces 
of soft iron, on which only are placed the 
magnetizing coils. 

A quick acting electro-magnet, in which 
the magnetizing coils are placed on soft iron 
pole pieces that are connected with and form 
the prolongations of the poles of a permanent 
horseshoe magnet. 

Hughes devised this form of electro-magnet in 
o-der to oVain th ; be t effects from currents of 
but short duration. 

He thus obtained a quick acting magnet, neces- 
sary to insure the success of his system of printing 
telegraph, where the magnetizing currents at 
times have a duration of but the .20 of a second. 



Mag.] 



340 



[Ma& 




Fig-. 37 y. Iron-Clad 
Electro- Magnet . 



Magnet, Electro, Joule's Cylindrical 

— An electro-magnet provided with a 

hollow cylindrical core. (See Magnet, Elec- 
tro, Cylindrical.) 
Magnet, Electro, Iron-Clad — An 

electro-magnet whose magnetizing coil is 
almost entirely surrounded by iron. 

The effect of the iron casing is to greatly re- 
duce the magnetic re- 
sistance of the circuit. 
A form of iron- clad elec- 
tro-magnet is shown in 
Fig. 377. Here one of 
the poles is connected 
with a casing of iron, 
external to the coils, and 
is thus brought nearer to 
the other pole. 

Magnet, Electro, 

Long-Core An electro-magnet with 

a long core of iron. 

A long-core electro-magnet magnetizes and 
demagnetizes much more slowly than a short- 
core electro-magnet. 

Magnet, Electro, Short-Core An 

electro-magnet with a short core of iron. 

A short-core electro-magnet possesses the power 
of being magnetized and demagnetized much more 
rapidly than a long core magnet. 

Magnet, Electro, Yoked-Horseshoe 

— A horseshoe electro-magnet, in which the 
two straight limbs are formed of two straight 
rods or bars, yoked together at one pair of 
ends by a yoke or bar of iron. 

In some cases the magnetizing coils are placed 
on each of the limbs. Sometimes, however, a 
single coil is placed at the middle of the yoke 
and the limbs are left bare. 

Even with the closest possible fitting the re- 
sistance of the magnetic circuit is much greater 
in this form of electro-magnet, owing to the 
smaller permeability of the air gap at the joints, 
than it would be if the entire core weie made of a 
single piece of iron. A yoked electro magnet is, 
however, more convenient to make and use. 

Magnet, Electro, Zigzag A multi- 
polar electro-magnet, the magnetizing coils 
ot which are separately wound in grooves 
cut in the face of straight or curved bars. 




A form of zigzag electro- magnet devised by 
Joule is shown in Fig. 378. The spiral char^ 
acter of the winding 
produces the alternate 
North and South polari- 
ties shown in the figure. 

Magnet, Equator of 

— A point ap- 
proximately midway 
between the poles of a 
straight bar magnet, or Fig 3?8 Zigzag Electro- 
nearly midway from Magnet. 
the poles of a horseshoe magnet if meas- 
ured along the bar from each pole. 

This term was proposed by Dr. Gilbert. It is 
now almost entirely displaced by the term neutral 
point. 

Magnet, High-Resistance A term 

sometimes used in place of long-coil magnet 
whose coils have a high electric resistance. 
(See Magnet, Long-Coil.) 

The term long-coil magnet is, perhaps, the pre-^ 
ferable one, because the resistance of a coil, per 
se, has nothing to do with its magnetizing power r 
which is determined by its ampere turns. (See 
Turns, Ampere. Magnet, Long Coil.) 

Magnet, Horseshoe A magnetized 

bar of steel or iron bent in the form of a 
horseshoe or letter U. 

Magnet, Iron-Clad A magnet whose 

magnetic resistance is lowered by a casing of 
iron connected with the core and provided for 
the passage of the lines of magnetic force. 
(See Magnet, Tubular?) 

Magnet, Jacketed A term some- 

times applied to a form of iron-clad magnet . 
(See Magnet, Lron-Clad.) 

Magnet, Keeper of A mass of soft 

iron applied to the poles of a magnet through- 
which its lines of magnetic force pass. (See 
Field, Magnetic?) 

The keeper of a magnet differs from its arma- 
ture in that the keeper while acting as such is 
always kept on the poles to prevent loss of mag- 
netization, while the armature, besides acting as- 
a keeper, may be attracted towards, or, if an 
electro-magnet, be repelled from the magnet 
poles. While performing its functions the keeper 
is always fixed, the armature generally, though 



Mag. 



341 



|Mag. 



not always, is in-motion. A keeper is, of course, 
only used with permanent magnets. 

Opinion is divided as to the efficacy of the 
keeper in preventing loss of magnetization in 
certain cases. 

Magnet, Long-Coil —An electro- 
magnet whose magnetizing coil consists of 
many turns of thin wire. 

Mag-net, Low-Resistance —A term 

sometimes used in place of short-coil mag- 
net. (See Magnet, Short-Coil) 

This term, short-coil magnet, is the preferable 
one. 

Mag-net, Marked Pole of A name for- 
merly applied to that pole of a magnet which 
points approximately to the geographical 
north. 

If the pole of the magnet that points to the 
geographical north be in reality the north pole 
of the magnet, then the earth's magnetic pole in 
the Northern Hemisphere is of south magnetic 
polarity. In the United States, and Europe 
generally, this is regarded as the fact. 

The French, however, formerly called the 
pole of the needle that points to the earth's 
geographical north the south or austral pole. 
In America and England it is called the north pole, 
the marked pole, or the north-seeking pole, and 
the Northern Hemisphere is assumed to possess 
south magnetic polarity. (See Pole, Magnetic, 
Austral. Pole, Magnetic, Boreal.) 

Magnet, Moment of The effective 

force of a magnetic couple as obtained by 
multiplying one of the forces of the couple 
by the perpendicular distance between the 
directions of the forces. 

The moment of a magnet is equal to the prod- 
uct of the volume of the magnet and the in- 
tensity of magnetization, or simply its magnetiza- 
tion. 

Magnet, Natural A name some- 
times given to a lodestone. (See Lodestone.) 

Magnet, Neutral Line of (See 

Line, Neutral, of a Magnet.) 

Magnet, Permanent A magnet of 

hardened steel or other paramagnetic sub- 
stance which retains its magnetism for a long 
time after being magnetized. 



A permanent magnet is distinguished, m this 
respect, from a temporary magnet of soft iron, 
which loses its magnetization very shortly after 
being taken from (.he magnetizing field. 

Magnet, Portative Power of The 

lifting power ot a magnet. 

The portative or lifting power of a magnet,. 
depends on the form ot the magnet, as well as on 
its strength. A horseshoe magnet, for example, 
will lift a much greater weight than the sane 
magnet if in the form ot a straight bar. 

This is due not only to the mutual action of the 
approached poles, but also to the decreased re- 
sistance of the magnetic circuit, and to the 
greater number of lines of magnetic force chat- 
pass through the armature. The portative power 
is proportional to the area of contact and the 
square of the magnetic intensity, the formula- 
being 

AXB^ 
8 it X 981, 
in which P, is the lifting power in grammes, A,, 
the area of contact in square centimetres, and B, 
is the number of lines of force per square centi- 
metre. 

Magnet Operation. — (See Operation, 
Magnet) 

Magnet, Receiving A name some- 
times given to the relay of a telegraphic sys- 
tem. (See Relay) 

In general, any magnet, used directly in the 
receiving apparatus, at the receiving end of a 
line connecting a system of electric communi- 
cation between transmitting and receiving 
instruments. 

Magnet, Regulator A magnet, the 

operation of which is to automatically effect 
any desired regulation. 

The magnet in the Thomson-Houston sys-* 
tern of automatic regulation, by means of 
which the commutator collecting brushes are 
automatically shifted to such positions on the 
commutator as will maintain the current 
practically constant, despite the changes in •» 
the resistance of the circuit external to the 
machine. (See Regulation, Automatic) 

Magnet, Relay An electro-magnet, 

whose coils are connected to the main line of 
a telegraphic circuit, and the movements of 



Mag.] 



342 



[Mag. 



whose armature is employed to bring a local 
battery into action at the receiving station, 
the current of which operates the register or 
sounder. 

Magnet, Short-Coil An electro- 
magnet whose magnetizing coil consists of a 
few turns of short, thick wire. 

Magnet, Simple A simple mag- 
netized bar. 

The term simple magnet i^ used in contradis- 
tinction to compound magnet. (See Magnet, 
Compound. ) 

Magnet, Sluggish A magnet that 

magnetizes or demagnetizes sluggishly. 

An electro-magnet becomes sluggish when sur- 
rounded by a sheathing of copper, on account of 
the currents induced in the sheathing in a direction 
opposite to those passing through the magnetizing 
coil. 

Magnet, Solenoidal A thin, uni- 
formly magnetized straight bar of steel, of 
such a length that its poles, situated at ex- 
tremities or ends of its longer axis, act on 
external objects as if equal and opposite quan- 
tities of magnetism were concentrated at such 
extremities. 

It derives its name solenoidal from the simi- 
larity between its action and that of a solenoid. 
Unless very carefully magnetized, a magnet will 
not act as a solenoidal magnet. (See Magnet, 
.Electro. Magnetism, Solenoidal Distribution of.) 

Magnet, Tubular A form of horse- 
shoe magnet, in which one pole is brought 
near the opposite pole by a hollow cylinder 
or tube of iron, which is placed in contact 
with one of the magnetic poles, so as to com- 
pletely surround the other, except in the plane 
of cross-section of that pole. 

A form of iron-clad magnet. (See Mag- 
net, Iron-Clad.) 

There is thus obtained a magnet, with two 
concentric poles, one solid and the other annular, 
the portative power of which is much greater than 
that of a horseshoe magnet of equal dimensions. 

Magnet, Field, of Dynamo-Electric Ma- 
chine One of the electro-magnets em- 
ployed to produce the magnetic field of a dy- 
namo-electric machine. 



The field magnets consist of a suitable frame, 
or we, on which the field magnet coils are 
wound. 

The field magnet cores, are made of thick and 
solid iron, as soft as possible. They should con- 
tain plenty of iron in order to avoid too ready 
magnetic saturation. 

All edges and corners are to be avoided, since 
they tend to cause an irregular distribution of the 
field. 

The field magnets should in general have suffi- 
cient magnetic strength to prevent the magnet- 
izing effect of the armature from unduly influ- 
encing the field, and thus, by causing too great a 
lead, produce injurious sparking. 

Magnetic or Magnetical. — Pertaining to 
magnetism. 

Magnetic Adherence.— (See Adherence, 
Magnetic?) 

Magnetic Air Circuit. — (See Circuit, Air, 
Magnetic?) 

Magnetic Air Gap.— (See Gap, Air, Mag- 
netic?) 

Magnetic Attraction. — (See Attraction, 
Magnetic?) 

Magnetic Axis.— (See Axis, Magnetic?) 
Magnetic Axis of a Straight Needle. — 

(See Axis, Magnetic, of a Straight Needle?) 
Magnetic Azimuth. — (See Azimuth, Mag- 
netic?) 

Magnetic Battery.— (See Battery, Mag- 
netic?) 

Magnetic Bridge.— (See Bridge, Mag- 
netic?) 

Magnetic Circuit.— (See Circuit, Mag- 
netic?) 

Magnetic Closed-Circuit. — (See Circuit, 
Closed Magnetic?) 

Magnetic Conductance. — (See Conduct- 
ance, Magnetic?) 

Magnetic Core, Closed (See Core, 

Closed-Magnetic?) 

Magnetic Core, Open (See Core, 

Open-Magnetic.) 

Magnetic Couple.— (See Couple, Mag- 
netic?) 



Mag.] 



343 



[Mag. 



Magnetic Curves.— (See Curves, Mag- 
netic) 
Magnetic Day of Disturbance.— (See Day 

of Disturbance, Magnetic) 

Magnetic Declination. — (See Decima- 
tion.) 

Magnetic Density. — (See Density, Mag- 
netic.) 

Magnetic Dip. — (See Dip, Magnetic) 

Magnetic Elements of a Place. — (See 
Elements, Magnetic, of a Place) 

Magnetic Equalizer. — (See Equalizer, 
Magnetic.) 

Magnetic Explorer. — (See Explorer, 
Magnetic) 



Magnetic, Ferro 



-Magnetic after 



the manner of iron or other paramagnetic 
body. (See Para?nag?ietic) 

Magnetic Field. — (See Field, Magnetic) 

Magnetic Field, Reversing (See 

Field, Magnetic, Reversing) 

Magnetic Field, Shifting (See 

Field, Magnetic, Shifting) 

Magnetic Figures. — (See Figures, Mag- 
netic. Field. Magnetic.) 

Magnetic Filament. — (See Filament, 
Magnetic) 

Magnetic Flow. — (See Flow, Magnetic) 

Magnetic Flux. — (See Flux, Magnetic) 

Magnetic Force. — (See Force, Magnetic.) 

Magnetic Inclination. — (See Inclination, 
Magnetic) 

Magnetic Induction. — (See Induction, 
Magnetic.) 

Magnetic Induction, Dynamic 

(See Induction, Magnetic, Dynamic.) 

Magnetic Induction, Static — (See 

Induction, Magnetic, Static) 

Magnetic Inertia. — (See Inertia, Mag- 
netic) 

Magnetic Intensity. — (See Intensity, 
Magnetic) 

Magnetic Joint. — (See Joint, Magnetic) 



Magnetic Lag. — (See Lag, Magnetic) 

Magnetic Latitude. — (See Latitude, Mag- 
netic.) 

Magnetic Leakage.— (See Leakage, Mag- 
netic) 

Magnetic Lines of Force. — (See Force, 
Magnetic, Lines of.) 

Magnetic Mass.— (See Mass, Magnetic) 

Magnetic Memory. — (See Memory, Mag- 
netic) 

Magnetic Meridian. — (See Meridian, 
Magnetic) 

Magnetic Moment. — (See Moinent, Mag- 
netic) 

Magnetic Normal Day.— (See Day, Nor- 
7nal, Magnetic) 

Magnetic Observatory. — (See Observa- 
tory, Magnetic.) 

Magnetic Output. — (See Output, Mag- 
netic) 

Magnetic Parallel. — (See Parallels, Mag- 
netic) 

Magnetic Permeability. — (See Permea- 
bility, Magnetic) 

Magnetic Permeance. — (See Permeance, 
Magnetic) 

Magnetic Permeation. — (See Permeation, 
Mag7ietic.) 

Magnetic Poles. — (See Poles, Magnetic) 

Magnetic Poles, False (See Pole, 

Magnetic, False.) 

Magnetic Proof Piece. — (See Piece, Mag- 
?ietic Proof) 

Magnetic Proof Plane. — (See Plane, 
Proof, Magnetic) 

Magnetic Reluctance. — (See Reluctance, 
Magnetic) 

Magnetic Repulsion. — (See Repuls-ion, 
Magnetic) 

Magnetic Resistance. — (See Resistance, 
Magnetic) 

Magnetic Retardation. — (See Retarda- 
tion, Magnetic.) 



Mag.J 



344 



[Mag.. 



Magnetic Retentivity .— (See Retentivity, 
Magnetic?) 

Magnetic Saturation.— (See Saturation, 
Magnetic) 

Magnetic Screen or Shield. — (See 

Screen or Shield, Magnetic?) 

Magnetic Screening.— (See Screening, 
Magnetic?) 

Magnetic Self-induction. — (See Induc- 
tion, Self, Magnetic?) 

Magnetic Shells. — (See Shells, Magnetic?) 

Magnetic Shunt. — (See Shunt, Magnetic?) 

Magnetic, Sidero A term proposed 

by S. P. Thompson to replace the term ferro- 
magnetic. (See Magnetic, Ferro.) 

Magnetic Solenoid.— (See Solenoid, Mag- 
netic?) 

Magnetic Sounds. — (See Sounds, Mag- 
netic?) 

Magnetic Spin. — (See Spin, Magnetic) 

Magnetic Storm. — (See Storm, Mag- 
netic?) 

Magnetic Strain. — (See Strain, Mag- 
netic) 

Magnetic Stress. — (See Stress, Magnetic) 

Magnetic Susceptibility. — (See Suscepti- 
bility, Magnetic) 

Magnetic Theodolite. — (See Theodolite, 
Magnetic) 

Magnetic Unit Pole. — (See Pole, Unit, 
Magnetic) 

Magnetic Units. — (See Units, Magnetic) 

Magnetic-Vane Ammeter. — (See Amme- 
ter, Magnetic- Vane) 

Magnetic-Vane Voltmeter. — (See Volt- 
meter, Magnetic- Vane) 

Magnetic Variations. — (See Variation, 
Magnetic) 

Magnetic Variation Transit. — (See Tran- 
sit, Magnetic Variation) 

Magnetic Variometer. — (See Variometer, 
Magnetic) 



Magnetic Viscosity. — (See Viscosity \ 
Magnetic) 

Magnetic Whirl.— (See Whirls, Mag- 
netic) 

Magnetic Whirl, Expanding (See 

Whirl, Magnetic, Expanding) 

Magnetics, Electro That branch 

of electric science which treats of the rela- 
tions that exist between electric circuits and 
magnets. 

Magnetism. — That branch of science which 
treats of the nature and properties of mag- 
nets and the magnetic field. (See Field, 
Magnetic) 

A property or condition of matter attended 
by the existence of a magnetic field. 

Magnetism, Ampere's Theory of A 

theory or hypothesis proposed by Ampere, to 
account for the cause of magnetism, by the 
presence of electric currents in the ultimate 
particles of matter. 

° oo o °o 

O 00° ° 

°ooo° 




Fig- 379' Unmagnetized Fig: 380. Magnetized 

Bar (after Ampere). Bar yafter Ampere). 

This theory assumes: 

( 1 . ) That the ultimate particles of all magneti- 
zable bodies have closed electric circuits in which 
electric currents are continually flowing. 

(2.) That in an unmagnetized body these cir- 
cuits neutralize one another because they have 
different directions. 

(3.) That the act of magnetization consists in. 
such a polarization of the particles as will cause 
these currents to flow in one and the same direc- 
tion, magnetic saturation being reached when all 
the separate circuits are parallel to one another. 

(4.) That coercive force is due to the resistance 
these circuits offer to a change in the direction 
of their planes. 

Figs. 379 and 380 show the circular paths of 
some of these circuits. Fig. 379 shows the as- 



Mag.] 



345 



[Mag. 



sumed condition of an unmagnetized bar. Fig. 
380 the assumed condition of a magnetized 
bar. 

A careful inspection of the figures will show that 
in a magnetized bar all the separate currents flow 
in the same direction. All the circuits except 
those on the extreme edge of the bar will, there- 
fore, have the currents flowing in them in opposite 
directions to that in their neighboring circuits, 
and, therefore, will neutralize one another. There 
■will remain, however, a current in a circuit 011 the 
outside of the bar, which must therefore be re- 
garded as the magnetizing current . 

Guided by these considerations, Ampere pro- 
duced a coil of wire, called a solenoid, which is 
the equivalent of the magnetizing circuit assumed 
by his theory. 

It therefore follows that an electric current sent 
through a coil of insulated wire surrounding a 
rod or bar of soft iron, or o'her readily magnet- 
izable material, will make the same a magnet. A 
magnet so produced is called an electro-magnet. 
(See Magnet, Electro.) 

The magnetizing coil is called a helix or sole- 
noid. (See Solenoid, Electro-Magnetic.) 

The polarity of the magnet depends on the 
direction of the current, or on the direction of 
winding of the helix cr solenoid. (See Solenoid, 
Sinistrorsal. Solenoid, Dextrorsal.) 

The improbability of an electric current con- 
tinually flowing in a circuit without the expendi- 
ture of energy, has led, perhaps, the majority of 
scientific men to reject Ampere's theory of mag- 
netism. 

Lodge, however, does not agree with the ma- 
jority of physicists in regarding a constant flow 
of electricity through the molecules of magnetiza- 
ble substances as an impossibility. On the sup- 
position that the atoms or molecules possess 
no resistance, the current would flow through 
them forever. He says: " To all intents and pur- 
poses certainly atoms are infinitely elastic, and 
why should they not also be infinitely conducting ? 
Why should the dissipation of energy occur, in 
respect to an electric current circulating wholly 
inside an atom •? There is no reason why it 
should. ' ' 

Magnetism, Animal A term some- 
times applied to hypnotism or artificial som- 
nambulism. 

Magnetism, Earth's, Theories as to Cause 

of The various theories or hypotheses 



respecting the cause of the earth's magnet- 
ism. 

Any theory or hypothesis which shall satisfac- 
torily explain the cause of the earth's magnetism 
must account for the following phenomena, viz.: 

(1.) Variations in the intensity of the earth's 
magnetic field. 

(2.) Variations in the earth's magnetic inclina- 
tion, declination and intensity. 

The following hypotheses have been proposed: 

1st. That the earth's magnetism is due to the 
circulation round the earth of electric currents 
produced by differences of temperature which the 
earth's surface acquires from exposure to the sun 
during its rotation. 

As the earth rotates from west to east, the area 
of greatest heat would move round the earth in 
the opposite direction, or from east to west. If 
now those differences of temperature could pro- 
duce, in a manner not as yet explained, thermo- 
electric currents circulating round the earth from 
east to west, such currents would produce, in the 
Northern Hemisphere of the earth, south mag- 
netic polarity, and in the Southern Hemisphere 
rorth magnetic polarity, which would account for 
the magnetic polarity of the earth. 

Differences in the intensity of the earth's mag- 
netic field, and in the inclination and direction of 
its lines of magnetic force, would be explained, 
according to this hypothesis, by the differences in 
the amount of the solar radiation at different 
times. 

The objection to this theory is to be found in 
the fact that by far the larger part of the earth's 
surface at the Equator is composed of water, so 
that the differences of potential at such parts, 
produced by the differences of temperature, are 
not readily set up in the earth's crust, if, indeed, 
they are set up at all. 

2d. That the earth's magnetism is due to in- 
duction from an already magnetized sun. This 
theory was brought forward by Secci and others. 
It is not generally credited. 

3d. A theory proposed by Biglow, which ac- 
counts for the earth's magnetism by rotation in 
the magnetic field of the sun's light and radia- 
tion. 

Biglow believes that the earth's magnetism is 
due to its rotation in the magnetic field of the 
sun's light. As the sun's light illumines one-hall 
of the earth's surface, the earth's rotation causing 
different portions of the surface to pass through 



Mag.] 



346 



[Mag. 



this illumined area, produces, in Prof. Biglow's 
opinion, those differences in the direction and in- 
tensity of the magnetic lines of the earth's field 
that correspond to differences in the earth's mag- 
netic intensity, declination and inclination. 

It will be observed that in all these theories the 
sun is the prime factor in the production of the 
earth's magnetism. 

The evident connection between the earth's 
magnetism and the solar radiation is established 
from the well known connection between the so- 
called magnetic storms and variations in the in- 
tensity of the earth's magnetism. 

Magnetic storms are always attended by out- 
bursts of solar energy, known technically as 
sun-spots. A series of observations on the num- 
bers and frequency of sun-spots, plotted in the 
form of a curve, the ordinates of which represent 
the times of occurrence of the spots and the 
abscissas, the number of such spots, prove that 
such curve agrees, in a remarkable manner, with 
a similar curve representing the variations of the 
earth's magnetic field. 

An evident connection, too, exists between the 
earth's magnetism and the prevalence of the 
aurora borealis. 

Magnetism, Electro — Magnetism 

produced by means of electric currents. 

The discovery by Oersted, in 1820, of the ac- 
tion of an electric current on a magnetic needle, 
was almost immediately followed by the simul- 
taneous and independent discoveries by Arago 
and Davy, of the method of magnetizing iron 
by the passage of an electric current around it. 

These observations were first reduced to a 
theory by Ampere. (See Magnetism, Ampere'' s 
Theory of. Magnet ', Electro.) 

Magnetism, Ewing's Theory of A 

theory of magnetism oroposed by Prof. 
Ewing, based on the assumption of originally 
magnetized particles. 

Ewing 's theory of magnetism assumes that the 
ultimate particles of matter are naturally mag- 
netic and possess polarity. In this respect Ewing 's 
theory agrees with the theories of Hughes and 
Weber. Ewing does not believe, however, in the 
necessity for the assumption of any arbitrary re- 
straining or constraining force to the movements 
of these ultimate magnetic particles other than 
those due to their own mutual magnetic attractions 
and repulsions. He assumes that in a magnet, 



the centres about which the molecular magnets^ 
rotate are maintained at constant distances from 
one another, save only as they are affected by the 
action of strain. 

He has experimentally demonstrated the prin- 
ciples of his theory by means of a model in which 
a number of small magnetic needles are so sup- 
ported as to be capable of free motion in a hori- 
zontal plane, when under varying magnetic 
forces. 

According to Ewing, "magnetic hysteresis" 
is not the result of any quasi-fnctional resistance 
to molecular rotation, but arises from a molecule 
moving from one position of stable equilibrium to 
another position of stable equilibrium through a> 
position of unstable equilibrium. "This pro- 
cess," says Ewing, " considered mechanically, is 
not reversible. The forces are different for the 
same displacement, going and coming, and there 
is dissipation of energy. In the model, the energy 
thus expended sets the little bars swinging, and 
their swings take some time to subside. In the 
actual solid, the energy which the molecular 
magnet loses as it swings through unstable posi- 
tions, generates eddy currents in surrounding 
matter. Let the magnets of the model be 
furnished with air vanes to damp their swings 
and the correspondence is complete." 

In Hughes' modification of Weber's theory of 
magnetism, it was held, that when magnetized 
iron was suddenly demagnetized by torsion or 
flexure, it lost its magnct.zaiion because the mo- 
lecular magnets came to rest in closed chains, wnich 
produced no external effects. Experimentation 
with Ewing's model of a magnet shows that when 
the separate magnets after having been placed in 
any particular grouping are permitted to come to 
rest free from any external magnetic force, they do 
not arrange themselves in closed chains, but in 
general the tendency appears to be the formation 
of lines consisting of two, three or more magnets 
each member of a line being strongly controlled 
by its next member in that line, but influenced 
by the neighbors which lie off the line on either 
side. 

The fact that a given force, suddenly applied, 
produces more magnetic induction than when 
gradually applied, and leaves less residual mag- 
netism when suddenly than when gradually re- 
moved is presumably due to the inertia of the 
molecules. 

The influence of mechanical, vibration in in- 
creasing the magnetic susceptibility and decreas- 



Mag.J 



347 



[Mag. 



ing the magnetic retentiveness, is ascribed by 
Ewing to the fact that the vibrations cause 
periodic variations in the distances between the 
centres of rotation of the magnetic molecules; 
thus making the molecular magnets respond more 
readily to changes of magnetic force during the 
time they are moving away from one another, 
when their magnetic stability is less, but also in- 
creasing the ease with which they respond to 
changes of magnetic force, by causing them to 
swing. 

Ewing discusses the theoretical effects of tem- 
perature on magnetism as follows, viz.: Suppose 
a moderate magnetizing force to be applied so 
that nothing like saturation is obtained, if now 
the temperature be raised; then 

(i.) The magnetic permeability increases until 
the temperature reaches a certain (high) critical 
value. 

(2.) At this temperature there is suddenly an 
almost complete disappearance of magnetic 
quality. 

He explains these facts as follows, viz.: An 
increase of temperature by increasing the distance 
between the molecular centres causes a decrease 
in their stability. 

The loss of magnetic qualities, when a certain 
temperature is reached, is, he believes, due to the 
fact that at such temperatures the magnetic 
molecules are set into actual rotation, when, 
naturally, all traces of polarity would disappear. 

Ewing's theory of magnetism also accounts to 
a considerable ext<~nt for the effects of stress and 
consequent elastic strain on the magnetic qualities 
of iron, nickel and cobalt. 

The following general summary of his theory 
is taken mainly from Prof. Ewing's original 
articles as published in the Journal of the Society 
of Arts: 

(i.) That in considering the magnetization of 
iron and other magnetic metals to be caused by 
the turning of permanent molecular magnets, we 
may look simply to the magnetic forces which 
the molecular magnets exert upon one another as 
the cause of their directional stability. There is 
no need to suppose the existence of any quasi- 
elastic directing force, or any quasi-frictional re- 
sistance to rotation. 

(2. ) That the intermolecular magnetic forces are 
sufficient to account for all the general character- 
istics of the process of magnetization, including 
the variations of susceptibility which occur as 
the magnetizing force is increased. 



(3.) That the intermolecular magnetic forces 
are equally competent to account for the known 
facts of retentiveness and coercive force, and the 
characteristics of cyclic magnetic processes. 

(4.) The magnetic hysteresis and the dissipation 
of energy which hysteresis involves are due to 
molecular instability, resulting from intermolec- 
ular magnetic actions, and are not due to any- 
thing in the nature of frictional resistance to the 
rotation of the molecular magnets. 

(5 . ) That this theory is wide enough to admit an 
explanation of the differences in magnetic quality 
which are shown by different substances, or by 
the same substance in different states. 

(6.) That it accounts in a general way for the 
known effects of vibration, of temperature, and 
of stress, upon magnetic quality. 

(7 ) That, in particular, it accounts for the 
known fact that there is hysteresis in the relation 
of magnetism to stress. 

(8.) That it further explains why there is in 
magnetic metals hysteresis in physical quality 
generally with respect to stress. 

(9.) That, in consequence, any (not very small) 
cycle of stress occurring in a magnetic metal in- 
volves dissipation of energy. 

It can be demonstrated by means of experi- 
ments with a model constructed according to 
Ewing's hypothesis, that this hypothesis comes 
nearer than any which had been proposed before 
in explaining the following effects: 

(1.) The behavior of a piece of iron when 
placed in a magnetic field whose strength is made 
to pass through a cycle of changes. 

(2.) That nearly all reversals of sign on the 
change of the magnetizing force are accompanied 
by small changes in the magnetization. 

(3.) That a piece of iron submitted to vibra- 
tions or mechanical shocks, is magnetized and 
demagnetized more readily and with a smaller 
hysteresial area than if it had remained undis- 
turbed by vibrations. 

(4.) The phenomenon of "time lag " in mag- 
netization. 

(5.) The phenomena of stress, both those which 
occur when a body has first been placed in a 
magnetic field and the stress made to vary, and 
those which occur when a body is first placed in 
a constant stress and the magnetizing force is 
made to vary. 

(6.) The effects of heat on magnetization, both 
as regards the effect of comparatively low heating 
on increase of magnetic susceptibility, and the 



Mag.l 



348 



[Mag. 



effect of excessive heating to decrease the sus- 
ceptibility. 

The author is indebted for the above summary 
of demonstrable facts to a paper recently read be- 
fore the Electrical Section of the Franklin Insti- 
tute^ by Prof. Henry Crew. 

Magnetism, Flux or Flow of The 

quantity of magnetism, or the number of 
lines of force which pass in any magnetic 
circuit under a given magneto-motive force, 
against a given magnetic reluctance. 

Magnetism, Galvano A term some- 
times used for electro-magnetism. 

Electro-magnetism is by far the preferable 
term, and is almost universally used in the United 
States. 

Magnetism, Horizontal Component of 

Earth's (See Component, Horizontal, 

of Earth's Magnetism.) 

Magnetism, Hughes' Theory of A 

theory propounded by Hughes to account for 
the phenomena of magnetism apart from the 
presence of electric currents. 

Hughes' theory, or, more strictly speaking, 
hypothesis of magnetism, though very similar to 
that of Ampere, does not assume the improbable 
condition of a constantly flowing electric current. 

Hughes' hypothesis assumes: 

(i.) That the molecules of matter, and, per- 
haps, more probably, the atoms, possess naturally 
opposite magnetic polarities, which are respect- 
ively + and — , or N and *S. 

(2.) That these molecules, when arranged in 
closed chains or circuits, are capable of neutral- 
izing one another so far as external action is con- 
cerned. 

m o n s n a 



/ 



% 






S* 



I 



n <? 



n s n s 

Fig. 38 1. Closed Molecular Chain. 

Two such arrangements or groupings are 
shown in Figs. 381 and 382. It will be observed 
that the magnetic chain or circuit is complete, 



and that, therefore, the substance can possess no 
magnetic properties so far as external action is 
concerned. 



«« na n 8 nans n s n 8 n s n e n a 

-WHI4H4Hli-H4H+ 

• n an 8 n an 8 n an an sn an s n 



Fig. 382. Closed Groupings. 

(3.) That the act of magnetization consists in 
such a rotation of the molecules that a polariza- 
tion of the substance is effected— that is, the 
molecules are rotated on their axes so that one set 
of poles tend to point in one direction and the 
other set of poles in the opposite direction. 

Partial magnetization consists in partial polari- 
zation. Magnetic saturation is reached v hen the 
polarization is complete. (See Saturation, Mag- 
netic. ) 

Coercive force is the resistance the body offers 
to the polarization or rotation of its molecules. 
(See Force, Coercive.) 

Hughes' hypothesis of magnetism would ap- 
pear to be strengthened by the following facts: 

(1.) A bar of steel or iron is sensibly elongated 
on being magnetized. This would naturally re- 
sult if the molecules be supposed to be longer in 
one direction than in any other. 

(2.) A tube, furnished at its ends w.th plates of 
flat glass and filled with water containing finely 
divided magnetic oxide of iron, is nearly opaque 
to light when unmagnetized, but will permit some 
light to pass through it when magnetized. 

(3.) A magnet, if cut at its neutral point, will 
possess opposite polarities at the cut ends; and, 
no matter to what extent this subdivision is car- 
ried, the particles will still possess opposite polar- 
ities. 

These facts are, however, also explained by 
Ampere's hypothesis of magnetism, with, how- 
ever, the improbable assumption of a constantly 
flowing current in each molecule. 

The following experiment by Von Betz tends 
somewhat to confirm Hughes' hypothesis: 

He placed a powerful horseshoe magnet in a 
solution of iron and deposited a bar or plate of 
metallic iron between the poles by electrolysis. 
Here the molecules, at the time of their deposi - 
tion, were subjected to a polarizing force which 
tended to place them all in the same direction, 
and, as the solution from which they were ob- 
tained permitted great freedom of motion, they 
were all presumably deposited in lines parallel t > 
one another. When this bar of iron was subs. 



Mag.] 



349 



[Mag. 



quently magnetized it was found to be much more 
powerful in comparison to its size than any other 
magnet. 

Mr. Shelford Bid well has shown that the act of 
magnetization produces a shortening rather than 
a lengthening of the magnetizable material. 
When the magnetization is moderate there is a 
true lengthening of the material, but when a 
more powerful magnetizing force is exerted a 
true contraction or shortening is observed. 



(F§« 



li 



■4» s 

Fig. 383. Bidwell Apparatus. 

The Bidwell apparatus is shown in Fig. 383. 
The bar of iron to be magnetized is shown at 
R R. The magnetization is obtained by means of 
the coil of wire C. The upper end of the bar 
presses against the rod L, fulcrumed at F. The 
other end of the bar bears against a pivoted 
mirror M, from which a spot of light is reflected. 

In the case of the magnetization of nickel, the 
experiments of Bidwell showed the existence of 
contraction for both weak and strong currents. 
This contraction is much greater than in the case 
of iron. 

Magnetism, Lamellar Distribution of 

— The distribution of magnetism in 

magnetic shells. 

A term sometimes applied to such a dis- 
tribution of magnetism in a plate, that the 
magnetized particles are arranged with their 
greatest length in the direction of the thick- 
ness of the plate, so that the poles are situ- 
ated at the faces of the plate, and conse- 
quently the extent of such polar surfaces is 
great when compared with the thickness of 
the plate. 

The term lamellar distribution of magnetism is 
used in contradistinction to solenoidal distribution. 
(See Magnetism, Solenoidal Distribution of J) 

A thin sheet or disc of magnetized material 
whose opposed extended faces are of opposite 



magnetic polarities, and the extent of whose sur- 
face is very great as compared with its thickness, 
is sometimes called a magnetic shell. 

The field produced by a magnetic shell is ex- 
actly similar to that produced by a closed voltaic 
circuit, the edges of the space inclosed by which 
correspond to the edges of the magnetic shell. 

The magnetic intensity, or the number of lines 
of force per unit area of cross-section, is equal 
over all parts of the surface of a simple magnetic 
shell. 

A magnetic shell may be conceived as consist- 
ing of a very great number of short, straight 
magnetic needles, placed side by side, with their 
north poles terminating at one of the faces of the 
sheet and their south poles at the opposite face, 
the breadth of the sheet being very great as com- 
pared with its thickness. Such a distribution of 
magnetism is known as a lamellar distribution. 

Magnetism, Residual The magnet- 
ism remaining in the core of an electro-mag- 
net on the opening of the magnetizing cir- 
cuit. 

The small amount of magnetism retained 
by soft iron when removed from any mag- 
netizing field. 

When hard iron or steel is removed from a mag- 
netizing field it retains nearly all its magnetism. 
Such magnetism is also, in reality, residual mag- 
netism, but the term is generally limited to the 
case of soft iron. 

Magnetism, Solenoidal Distribution of 

A term sometimes applied to such 

a distribution of magnetism in a bar that 
the magnetized particles are arranged with 
their poles in the direction of the length of the 
bar, the ends of which are of opposite mag- 
netic polarities, and the extent of whose sur- 
faces is small as compared with the length 
of the bar. 

The term solenoidal distribution is used in con- 
tradistinction to lamellar distribution. (See Mag- 
izetism, La?7iellar Distribution of. ) 

Magnetism, Strength of A term 

sometimes used in the sense of intensity of 
magnetization. (See Magnetization, Inte?i- 
sity of) 

The term, strength of magnetism, is sometimes 
used for flux or quantity of magnetism. 

Intensity of magnetization, is the preferable 
term. 



Mag.] 350 

Magnetism, Terrestrial A name 

applied to the magnetism of the earth. 

Terrestrial magnetism has been ascribed to a 
variety of causes. (See Magnetism, Earth's, 
Theories as to Cause of. ) 

Magnetism, Vertical Component of 

Earth's (See Component, Vertical, 

of Earth's Magnetism.) 

Magnetite. — Magnetic oxide of iron, or 
Fe 3 4 , found in nature, as an ore or mineral. 

Lode-stone consists of pieces of magnetized 
magnetite. 

Magnetizable. — Capable of being magnet- 
ized after the manner of a paramagnetic sub- 
stance like iron. 

The most magnetizable metals are iron, nickel, 
cobalt and manganese. (See Paramagnetism.) 

Magnetization. — The act of calling out or 
of endowing with magnetic properties. 

Magnetizable substances are magnetized by 
being placed in magnetic fields. (See Field, Mag- 
netic. Magnetization, Methods of. ) 

The act of initial magnetization is not exactly 
the same as the act of subsequent magnetization. 

A piece of steel, which has once been magnet- 
ized and subsequently demagnetized, is a thing en- 
tirely distinct, as regards its magnetization, from 
a piece of steel which has never before been mag- 
netized, and such a piece can never be placed ex- 
actly in the same position as regards a magnet- 
izing force, unless it is actually melted and recast, 
or, perhaps, maintained for a comparatively long 
time at a white heat. 

Magnetization, Anomalous The 

magnetization obtained from an oscillatory 
discharge, such as that of a Leyden jar. 

In 1842, Henry described the real character of 
anomalous magnetization, and showed that there 
was nothing anomalous in such magnetization, but 
rather in the fact that the magnetizing currents 
possessed no simple direction. He remarks on 
this subject as follows: 

"This anomaly, which has remained so long 
unexplained, and which, at first sight, appears at 
variance with all our theoretical ideas of the con- 
nection of electricity and magnetism, was, after 
considerable study, satisfactorily referred to an 
action ot the discharge of a Leyden jar which had 
never before been recognized. The discharge, 



[Mag, 

whatever may be its nature, is not correctly rep- 
resented (employing the simplicity of Franklin) 
by the single transfer of an imponderable fluid 
from one side of the jar to the other ; the phe- 
nomena require us to admit the existence of a. 
principal discharge in one direction and then 
several reflex actions backward and forward, each 
more feeble than the preceding, until the equi- 
librium is obtained. All the facts are shown to 
be in accordance with the hypothesis, and a ready 
explanation is afforded by it of a number of phe- 
nomena which are to be found in the older works 
on electricity, but which have until this time re- 
mained unexplained. ' ' 

Magnetization by Touch. — The produc- 
tion of magnetism in a magnetizable sub- 
stance by touching it with a magnet. 

There are three methods of magnetization by 
touch, viz.: 

(1.) Singletouch. 

(2.) Separate touch. 

(3.) Double touch. 

In single touch, the magnetization of a bar of 
iron or other magnetizable material is effected by 
the touch of a single magnet. 

In Single Touch, the magnetizing magnet is 
drawn over the bar to be magnetized from end to 
end and returned through air, the stroke being 
repeated a number of times. The end of the 
bar the magnet leaves is magnetized oppositely 
to the magnetizing pole. 

By some writers the method of single touch is 
described as that effected 
by placing the magnet- 
izing magnet N S (Fig. 
384) on the middle of 
the bar to be magnetized, 
and drawing it to the 
end and returning 
through the air as be- 
fore, and then reversing 
the pole, placing it on 
the middle of the bar 



+ N 



S — 



Fi\ 



384. Magnetization 
by Single Touch. 

and drawing it towards the other end. The 



he: 





■jH E 



Fig. 385. Magnetization iy Separate Touch. 

former would, however, appear to be the better 
use of the term single touch. 

In Separate Touch, two magnetizing bars are 
placed with their opposite poles at the middle 



Mag.] 



351 



LMag. 



of the bar to be magnetized and drawn away from 
each other towards its ends, as shown in Fig. 
385. This motion is repeated a number ot times, 
the poles being each time returned through the 
air. 

In the above, as in all cases of magnetization 
by touch, better effects are produced, if the bar 




Fig. 386. Magnetization by Double Touch. 

to be magnetized is rested on the opposite poles 
of another magnet, or, as shown in Fig. 386, 
placed near them. 

In Double Touch the two magnets are placed 
with their opposite poles together on the middle 
of the bar to be magnetized, as shown in Fig. 
386. They are then moved to one end of the bar, 
when, instead of removing them and passing them 
back through the air to the other end, they are 
moved over the surface of the bar to be magnet- 
ized to the other end, and these to and-fro mo- 
tions are repeated a number of times. The mo- 
tion is stopped at the middle of the bar, when the 
magnetizing magnets are moving in the opposite 
direction to that at which they began to move. 
This insures an equal number of strokes to the 
two halves of the bar. The method of double 
touch produces stronger magnetization than 
either of the other methods, but does not effect 
such an even distribution of the magnetism, and 
therefore is not applicable to the magnetization 
of needles. 

A variety of double touch is shown in Fig. 387, 
where four bars, to be magnetized, are placed in 
the form of a hollow rectangle, with only their 
ends touching at their edges, the angular spaces 




Fig. 387. Magnetization by Double Touch. 

at the corners being filled with pieces of soft iron. 
The horseshoe magnet N S, is then moved around 
the circuit several times in the same direction. 
This is believed to produce a more uniform mag- 



netization than the ordinary method of double 
touch. 

Magnetization, Co-efficient of A 

number representing the intensity of magnet- 
ization produced in a magnetizable body, 
divided by the magnetizing force H. 

Calling k, the co-efficient of magnetization ; I, 
the intensity of the resulting magnetization, and 
H, the magnetizing force producing it, then 

The co-efficient of magnetization is sometimes 
called the magnetic susceptibility. 

A paramagnetic body when placed in a mag- 
netic field concentrates the lines of magnetic force 
on it, or causes them to pass through it. The 
intensity of the magnetization so produced de- 
pend s, therefore, 

(1.) On the intensity of the magnetizing field. 

(2.) On the ability of the metal to concentrate 
the lines of force on it; that is, on the nature of 
the metal, or on its magnetic permeability. (See 
Permeability, Magnetic. Paramagnetism. Dia- 
magnetism. ) 

'J he intensity of magnetization will, therefore, 
be equal to the product of the co-efficient of mag- 
netization and the intensity of the magnetizing 
field. It will, also, of course, depend on the area 
of cross-section of the magnetized body. 

The co-efficient of magnetization ofparamag- 
netic bodies is said to be positive, and that of dia- 
magnetic bodies to be negative, because paramag- 
netic bodies concentrate the lines of magnetic 
force on them, while diamagnetic bodies appear 
to repel the lines of force. (See Paramagnetic. 
Diamagnetic. ) 

Magnetization, Critical Current of 

— The current at which any certain or definite 
effect of magnetization is produced. 

Magnetization, Intensity of — A 

quantity showing the intensity of the magnet- 
ization produced in a substance. 

A quantity showing the intensity with 
which a magnetizable substance is mag- 
netized. 

The intensity of magnetization depends: 

(1.) On the intensity of the magnetizing field. 

(2.) On the magnetic permeability, or on the 
conducting power of the substance for lines of 
magnetic force. 



Mag.; 



352 



[Mag. 



The greater the strength of the magnetizing 
field, and the greater the magnetic permeability, 
the greater is the intensity of the magnetization 
produced. 

When, therefore, a magnetizable substance is 
placed in a magnetizing field, the intensity of the 
magnetization will depend on the magnetic sus- 
ceptibility of the substance; that is, on the ratio of 
the induced magnetization to the magnetizing force 
producing it. 

Soft iron has a high co-efficient of magnetization, 
or its magnetic susceptibility is high. (See Sus- 
ceptibility, Magnetic. Magnetization, Co-efficient 
of.) 

The intensity of magnetization through a sub- 
stance is measured by dividing the magnetic 
moment by the magnetic volume. 

If a bar of soft iron is placed with its greatest 

length extending in the direction of the lines of 

force in a magnetic field, it will have induced in 

it a certain intensity of magnetization which may 

be expressed as follows: 

m . 1 
Intensity of Magnetization = y Q i um = k H, 

where m, equals the strength of the magnet ; 1, its 
length ; k, the co-efficient of magnetization, and 
H, the intensity of the magnetizing field. — (S. P. 
Thompson.) 

" The moment of a magnet, or of any element 
of a magnet, may be considered numerically to be 
made up of two factors, one, its volume, and the 
other its intensity of magnetization, or simply 
its magnetization, and hence, for a uniformly mag- 
netized small linear needle, we may define the 
intensity of its magnetization by saying that it has 
magnetic moment of unit volume." — {Fleming.) 

Magnetization, Maximum A term 

sometimes used for magnetic saturation. 

Urquhart states, as the result of numerous ex- 
periments, that the number of lines of magnetic 
force that usually pass through a bar of soft iron 
I square centimetre in area of cross- section, when 
magnetized to a maximum, is equal to 32,000. 
Ewing gives the number in the particular case of 
a very extraordinary magnetization as being equal 
to 45,350 per square centimetre area of cross- 
section. 

Magnetization, Methods of Mag- 
netization effected either by induction from 
another magnet, or by means of induction by 
an electric current. 



The substance to be magnetized is brought into 
a magnetic field, so that the lines of magnetic 
force pass through it. All methods of magnet- 
ization may be divided into methods of magnetiza- 
tion by tonch and magnetization by the electric 
current. (See Magnetization by Touch.) 

Magnetization, Permanent, Intensity of 

A term employed for the intensity of 

a permanent magnetization produced in hard 
steel, as distinguished from the magnetization 
temporarily produced in soft iron. (See Mag- 
7ietization, Intensity of ".) 

Magnetization, Temporary, Intensity of 

The intensity of the magnetization 

temporarily induced in a bar of soft iron, as 
distinguished from permanent magnetization 
induced in hard steel. (See Magnetization, 
Intensity of) 

Magnetization, Time-Lag of A lag 

which appears to exist between the time of 
action of the magnetizing force and the ap- 
pearance of the magnetism. 

The time which must elapse in the case of 
a given paramagnetic substance before a mag- 
netizing force can produce magnetization. 

In the opinion of some physicists there is no 
such thing as a true magnetic time-lag, the ap- 
parent time-lag being due entirely either to hys- 
teresis or to eddy currents. According to them, 
while the magnetizing force is increasing, it pro- 
duces, in the iron, reversely-directed surface- 
eddy -currents, which produce a reversed or 
opposed magnetizing force in the more deeply 
seated layers of the iron, the time-lag being due 
to the interval which is required for these eddy 
currents to die away and thus permit the mag- 
netizing force to produce its full magnetization. 

According to others, however, a true time- 
lag does exist entirely apart from the existence of 
surface-eddy-currents. 

Magnetize. — To endow with magnetic 
properties. 

Magnetized. — Endowed or impressed with 
magnetic properties. 

Magnetizing. — Causing or producing mag- 
netism. 

Magneto-Blasting Machine. — (See Ma- 
chine, Magneto-Blasting) 



Mag. 



353 



[Mag. 



Magneto-Electric Bell.— (See Bell, Mag- 
neto-Electric?) 

Magneto-Electric Brake.— (See Brake, 
Magneto-Electric?) 

Magneto-Electric Call-Bell.— (See Call- 
Bell. Mag?ieto-Electric.) 

Magneto-Electric Faradic Apparatus.— 

(See Apparatus, Faradic, Magneto-Elec- 
tric.) 

Magneto-Electric Induction.— (See In- 
ductio?i, Magneto- Electric.) 

Magneto-Electric Machine.— (See Ma- 
chine, Magneto-Electric?) 

Magneto-Electric Medical Apparatus.— 
(See Apparatus, Magneto- Electric Medi- 
cal) 

Magneto-Electricity,— (See Electricity, 
Magneto.) 

3Iagnetograph. — The permanent record 
obtained from the action of a self-recording 
magnetometer. (See. Magnetometer. Self- 
Be cor ding.) 

Magnetometer.— An apparatus for the 
measurement of magnetic force. 




The magnetometer shown in Fig. 388, consists 
of a magnetized bar suspended by two wires pass- 
ing over a pulley, as shown. The magnet is held 
by the frame S S, provided with a graduated scale 
K. The mirror S, is supported by a vertical post 
attached to the frame, and serves to reflect a scale 
placed below a distant reading telescope. This 
form of magnetometer, is called the bifilar mag- 
netometer, and was the one used by Gauss in his 
study of the earth's magnetism. 

A variety of forms have been given to delicate 
magnetometers. Some are self-recording. (See 
Magnetometer, Self- Recording. ) 

Magnetometer, Differential A form 

of magnetometer in which the principles of the 
differential galvanometer, as applied to the 
electric circuit, are applied to the magnetic 
circuit. 

The differential magnetometer of Eickemeyer is 
shown in Figs. 389 and 390. Its principles of 
operation will be understood from the following 
considerations. 

Referring to Fig. 389. Suppose F t and F 2 are 
two electromotive forces connected in series, and 
x and y, two resistances to be compared. Each of 
the resistances x and y, is shunted respectively by 
two conductors a and b, whose resistance we 
wish to compare. Since the action of each of 
them on the galvanometer G, is opposite, its nee- 
dle remains at zero, when the current in a, is 
equal to the current in b. 

If, instead of electric circuit, we take the idea 
of magnetic circuit or the number of lines of 
magnetic force, and instead of potential difference, 




Fig 3$&; Magnetometer. 

In some magnetometers the magnetic force is 
measured by the torsion of a wire, as in the tor- 
sion balance. (See Balance, Coulomb's Torsion.) 



Fig. 38q. Eickemeyer 's Differential Magnetometer. 

magneto-motive force, and instead of electric re- 
sistance, magnetic resistance, we have the princi- 
ples on which the Eickemeyer differential magnet- 
ometer is founded. 

The magnetic circuit of the d fferential magnet- 
ometer consists of two pieces ot soft iron, shaped 



Mag.] 



354 



as shown at F t and F 2 , Fig. 390. A magnetic 
coil C, surrounds the middle portion of each cir- 
cuit as shown. The operation as described by- 
Mr. Chas. Steinmetz, from whom the above de- 
scription is mainly taken, is as follows, viz. : ' ' The 
front part s x of the left iron piece becomes south, 
and the back part n ± north polarity; the front 
part of the right iron piece n 2 becomes north, and 
the back part south; and the lines of magnetic 
force travel in the front from the right to the left, 
from n g to Sj ; in the back the opposite way, from 
the left to the right, or from n 1 to s ; , either 
through the air, or, when n s and Sj, or iij and s 2 , 
are connected by a piece of magnetizable metal, 
through this and through the air. 

In the middle of the coil C, stands a small soft 
iron needle with an aluminum indicator, which 
plays over a scale K, and is held in a vertical 
position by the lines of magnetic force of the coil 
C, itself, deflected to the left by the lines of mag- 
netic force traversing the front part of the instru- 
ment from n 2 to s 1 , deflected to the right by the 
lines traversing the back from n 1 to s 2 . This 
needle shows by its zero position that the mag- 
netic flow through the air in front from n 2 to s x 
has the same strength as the magnetic flow in the 
back from n 1 to s 2 through the air. 

Now we put a piece of soft iron x on the front 
of the instrument. A large number of lines go 
through x, less through the air from n 2 to s x ; but 
all these lines go from n : to s 2 through the air 
at the back part of the magnetometer, the front 
part and back part of the instrument being con- 
nected in series in the magnetic circuit. There- 
fore the needle is deflected to the right by the 
magnetic flow in the back of the instrument. 

Now, we put another piece of iron, y, on the 
back part of the instrument, then equilibrium 
would be restored as soon as the same number of 
lines of magnetic force go through x, as through 
y, because then also the same number of lines go 
through air in the front as in the back. As will 
be noted, the air here takes the place of the resist- 
ances a and b, influencing the galvanometer 
needle G, as in the diagram Fig. 389. 

The operation of the instrument is exceedingly 
simple and is as follows : Into the coil C, an elec- 
tric current is sent which is measured by the am- 
meter A, and regulated by the resistance-switch 
R. Then the needle, which before had no fixed 
position, points to zero. 

Now, we lay the piece of iron, the magnetic 
properties of which we want to determine, on the 



back part of the instrument. The needle is de- 
flected to the left. On the front of the instrument 
we put Norway iron rods of known cross-section 
and known conductivity, until equilibrium is 
again restored. Then the iron in the front has 
the same magnetic resistance as the iron in the 
back, and the ratio of the cross- sections gives 
directly the ratio of the conductivities ; so that 
by a single reading the magnetic conductivity of 
any piece of iron can be compared with that of 
the Norway iron standard. 

For absolute determinations, the iron is turned 
off into pieces of exactly 4 square centimetres 
cross-section and 20 centimetres in length, both 
ends fitting into holes in large blocks of Norway 
iron, which are laid against the pole pieces of the 
magnetometer, so that the transient resistance 
from pole face to iron is eliminated. 




Fig, 3<?o. Eickemeyer's Differential Magnetometer, 

Magnetometer, Self-Record inj A 

self-recording apparatus, by means of which 
the daily and hourly variations of magnetic 
needles in the earth's field, at any locality, are 
continuously registered. 

The self recording magnetometer employed in 
the observatory at Kew, consists essentially of 
means of obtaining a photographic record of a 
spot of light reflected from a mirror, attached to 
the need'e whose variations are to be recorded. 
The photographic record is received on a strip of 
sensitized paper, maintained in uniform and con- 
tinuous motion by means of suitable clock-work. 
The record so obtained is called a magneto- 
graph. 

Magneto-Motive Force. — (See Force, 

Magneto-Motive.) 



Mag.] 



355 



[Mak. 



Magneto-Motive Force, Absolute Unit of 

(See Force, Magneto-Motive, Abso- 
lute Unit of.) 
Magneto-Motive Force, Practical Unit of 

(See Force, Magneto-Motive, Prac- 
tical Unit of.) 

Magneto-Optic notation. — (See Rotation, 
Magtieto-Optic) 

Magnetophone. — A species of magnetic 
siren in which sounds are produced in an 
electro-magnetic telephone by the periodic 
currents produced in its coils by the rotation 
of a perforated metallic disc in a magnetic 
field. 

As the speed of the disc increases, the pitch of 
the note increases. The apparatus was invented 
by Prof. Carhart, in 1883. A similar apparatus 
is useful in studying the distribution of the mag- 
netic field of a dynamo-electric machine. In this 
case, a small, thin coil of insulated wire is held in 
the different regions around the machine, while 
the telephone is held to the ear of the observer. 
Magnetic leakage, or useless dissipation of lines 
of magnetic force outside the field proper of the 
machine, is at once rendered manifest by the 
musical note caused by variations in the intensity 
of the field. 

Since the intensity of the note heard will vary 
according to the intensity of the field, and also 
according to the position in which the coil is held, 
such a coil becomes a magnetic explorer, and by 
its use the distribution and varying intensity of an 
irregular field can be ascertained. Its use is 
especially advantageous in proportioning dynamo - 
electric machines and electric motors. (See Ex- 
plorer, Magnetic. ) 

Magneto-Receptive Device. — (See Device, 
Magneto-Receptive) 

Magneto-Static Current Meter. — (See 
Meter, Current, Magneto-Static) 

Magneto-Static Screening. — (See Screen- 
ing, Magneto-Static) 

Magneto-Statics.— (See Statics, Magneto) 

Magneto-Therapy. — (See Therapy, Mag- 
neto) 
Main Battery. — (See Battery, Main) 
Main-Battery Circuit. — (See Circuit, 
Main-Battery) 



Main, Electric -The principal con- 
ductor in any system of electric distribution. 

Main Feeder. — (See Feeder, Standard or 
Main) 

Main Fuse.— (See Fuse, Main) 

Main, House A term employed in 

a system of multiple incandescent lamp dis- 
tribution for the conductor connecting the 
house service conductors with a centre of 
distribution, or with a street main. 

Main-Line Cut-Out — (See Cut-Out, Main- 
Line) 

Main, Street In a system of incan- 
descent lamp distribution the conductors ex- 
tending in a system of networks through the 
streets from junction box to junction box, 
through which the current is distributed 
from the feeder ends, through cut-outs, to 
the district to be lighted, and from which 
service wires are taken. 

Main, Sub A name sometimes 

given to the distributing conductor that is 
connected directly to a main. 

The branch nearest the main. (See 
Branch) 

Main Wire. — (See Wire, Main) 

Mains of Electric Railroads.— The wires 
or conductors used for carrying the current 
from the feeders through the tap wires to the 
trolley wires. 

Make. — A completion of a circuit. 

Make-and-Break. — The periodic alternate 
completion and opening of a circuit. 

Make-and-Break, Automatic A 

term sometimes employed for such a combi- 
nation of contact points with the armature of 
any electro-magnet, that the circuit is auto- 
matically made and broken with great rapidity. 

An automatic make-and-break is used in most 
forms of electric alarms in connection with some 
form of electric bell. (See Alarm, Electric.) 

It is also used in the Ruhmkorff ind action coil 
in order to produce the variations in the primary 
circuit. (See Coil Induction.) 

Make-Induced Current. — (See Current, 

Make-Induced) 



Mak.] 



356 



[Mar, 



Making 1 the Primary. — (See Primary, 
Making the.) 
Mallet, Electro-Magnetic Dental 

— (See Dental-Mallet, Electro-Magnetic.) 

Mangin Projector. — (See Projector, Man- 
gin.) 

Man-Hole, Compartment, of Conduit 

— A man-hole provided with suitably sup- 
ported shelves or compartments, guarded by- 
locked doors that protect different cable sec- 
tions. 

Man-Hole of Conduit. — An opening of 
sufficient size to admit a man, communi- 
cating from the surface of the roadbed with 
an underground conduit. 

Manipulator, Breguet's The send- 
ing instrument employed by Breguet in his 
system of step-by-step or dial telegraphy. 
(See Telegraphy, Step-by- Step.) 

Manometei.— An apparatus for measuring 
the tension or pressure of gases. 

Manometers are either mercurial or metallic. 
Mercurial manometers are of two classes, viz., 
manometers with free air and manometers with 
compre-sed air. 

Manometers measure the pressure of gases 
either in atmospheres, i. e., in multiples or deci- 
mals of 15 pounds to the square inch, or in inches 
of mercury. 

Map or Chart, Inclination A chart 

or map on which lines are drawn, showing 
the lines of equal dip or inclination, or the 
isoclinic lines. 

An inclination chart is shown in Fig. 391. 

It will be seen that the magnetic equator, or 
line of no dip, does not correspond with the geo- 
graphical equator, being generally north of the 
equator in the Eastern Hemisphere, and south of 
it in the Western. The figures attached to the 
lines indicate the value of the angle of dip. 

Map or Chart, Isodynamic A map 

of the earth on a mercator's projection, on 
which isodynamic lines are drawn. 

An isodynamic chart is shown in Fig. 392. It 
will be observed that the isodynamic lines do not 
exactly coincide with the isoclinic lines, since the 
line of least magnetic intensity does not correspond 
with the line of the magnetic equator. 

The point of least magnetic intensity is found at 



about lat. 20 degrees S., and Ion. 35 degrees W. 
The point of greatest magnetic intensity is found 
at about lat. 52 degrees N. and Ion. 92 degrees- 
W. 

Another, though weaker point of magnetic in- 
tensity, is found in Siberia. These are distin- 
guished from the true magnetic poles by the term 
Poles of Intensity. 

The Poles of Vertuity, as determined by the 
dipping needle, and the Poles of Intensity, as de- 
termined by the needle of oscillation, therefore do 
not coincide in the Northern Hemisphere. 

Map or Chart, lsogonal A term 

sometimes used for an isogonic map or chart. 

Map or Chart, Isotonic A chart 

on which the isogonal lines are marked. 

An isogonic map or chart is sometimes called 
a declination map or chart . 

In the declination or variation chart, shown in 
Fig. 393, the region of western declination is in- 
dicated by the shading. There is a remarkable 
oval patch in the northeastern part of Asia, in 
which the declination is west. A similar oval of 
decreased inclination is seen in the Southern 
Pacific. 

The entire earth acts like a huge magnet with 
south magnetic polarity in the Northern Hemi- 
sphere. 

It is not known whether the earth possesses 
but a single pair of magnetic poles or more 
than a single pair. The variations in the dec- 
lination, and in the intensity of its magnetism, 
due to the position of the sun, ss well as the 
marked magnetic disturbances that accompany 
the occurrence of sun spots, would appear to con- 
nect the earth's magnetism in some manner with 
the solar radiation. (See Magnetism, Earth 1 s y 
Theories as to Cause of.) 

Marine Galvanometer. — (See Galvanom- 
eter, Marine?) 

Mariner's Compass. — (See Compass, Azi- 
muth.) 

Marked Pole of Magnet— (See Magnet, 
Marked Pole of.) 

Markers. — Colored flags, or signal lights, 
generally green, displayed in systems of 
block railway signaling at the ends of 
trains, in order to avoid accidents from trains 
breaking in two. (See Railroads, Block 
System for?) 



Jttar.] 



357 



[Mar. 




Mar.] 



358 



[Mar, 




Mar.] 



3j0 



[Mar. 




Mas.] 



300 



[MaL 



Mass. — The quantity of matter contained 
in a body. 

Mass must be carefully distinguished from 
weight. The weight of a given quantity of 
matter depends on the attraction which the earth 
possesses for it, and this, on the earth's surface, 
varies with the latitude, being greatest at the 
poles and least at the equator. It also varies 
with different elevations above the level of the sea. 
The mass, however, is the same under all circum- 
stances, whether for different latitudes or alti- 
tudes, on the earth's surface. 

Mass Attraction. — (See Attraction, Mass.) 

Mass, Magnetic A quantity of mag- 
netism which at unit distance produces an 
action equal to unit force. 

Mass, Unit of The quantity of mat- 
ter which under certain conditions will balance 
the weight of a standard gramme or pound. 

The gramme is equal to the one-thousandth 
part of a piece of platinum called the kilogramme, 
depos ted as a standard in the archives of the 
French Government, and intended to be equal to 
the mass of i cubic centimetre of water at the tem- 
perature of its maximum density. 

Massage. — A treatment for the purpose 
of effecting changes in general nutrition or 
action of particular parts of the body, by 
kneading, rubbing, friction, etc. 

Massage, Electro The application 

of electricity to the body during its massage. 

Connections are established between the patient 
and a battery by connecting one electrode of a 
source to the kneading instrument, and the other 
electrode to the body of the patient. 

Masses, Electric A mathematical 

conception for such quantities of electricity 
as at unit distance will produce an attrac- 
tion or repulsion equal to unit force. 

Electrical masses are assumed to be equal when 
they produce on two identical bodies of small 
dimensions charges of the same electric force. 

Master Clock.— (See Clock, Master) 
Materials, Insulating — Non-con- 
ducting substances which are placed around a 
conductor, in order that it may either retain 
an electric charge, or permit the passage of 



an electric current through the conductor 
without sensible leakage. 

Various gases, liquids or solids may be em- 
ployed as insulators. A very high vacuum affords 
the best known insulation. 

Matter. — Anything which occupies space in 
three directions and prevents other matter f rom 
simultaneously occupying the same space. 

Matter is composed of atoms, which unite to 
form molecules. (See Ato?n. Molecule. ) 

Matter, Elementary — Matter which 

cannot be decomposed into simpler matter. 

Varieties of elementary matter are called 
elements. (See Element. ) 

Matter, Kinetic Theory of A 

theory which assumes that the molecules of 
matter are in a constant state of motion or 
vibration towards or from one another in 
paths that lie within the spheres of their 
mutual attractions or repulsions. 

The molecules of gases have great freedom 
of motion, and are so far removed from one 
another as to be but little, if any, influenced by 
their mutual attractions. They are therefore 
assumed to move in straight lines with very great 
velocity until they collide against one another, or 
against the sides of the containing vessel, when 
they are reflected and again move in straight lines 
in a new path. 

Matter, Radiant, or Ultra-Gaseous 

— A term proposed by Crookes for the 
peculiar condition of the gaseous matter which 
constitutes the residual atmospheres of high 
vacua. 

This is now generally recognized as a fourth- 
state of matter, these four states being: 

(i.) Solid. 

(2.) Liquid. 

(3.) Gaseous. 

(4. ) Ultra-gaseous or radiant. 

The peculiar properties of radiant matter are 
seen in the mechanical effects of the localized 
pressures produced when such residual atmos- 
pheres are locally heated or electrified. 

In Crookes' radiometer, vanes of mica, silvered 
on one face and covered with lampblack on the 
opposite face, are supported on a vertical axis so 
as to be capable of rotation and placed in a glass 
vessel in which a high vacuum is maintained. On 



Mat.1 



361 



[Mat. 



exposing the instrument to the radiation from a 
candle or gas flame, a rapid rotation takes place. 
(See Radiometer, Crookes\) 

The explanation is as follows : The lampblack 
covered surfaces absorb the radiant, heat, and be- 
coming heated, the molecules of gas in the residual 
atmosphere are shot violently from them, and by 
their reaction drive the vanes around in the 
opposite direction to that from which they are 
thrown off. The molecules are also shot off from 
the silvered surfaces, but, as these are cooler, the 
effect is not as great as at the blackened surfaces. 

In a gas, at ordinary pressure, the heated sur- 
faces are also bombarded by other molecules of 
the gas, but in high vacua the mean free path of 
the molecules is so great that there is no interfer- 
ence, a Crookes* layer existing between the vanes 
and the walls of the glass vessel. (See Layer, 
Crookes\) 

When a Crookes' tube is furnished with suit- 
able electrodes, and electric discharges are sent 
through it between these electrodes, a stream of 
molecules is thrown off in straight lines from the 
surface of the negative electrode. 

Some of the effects of this molecular bombard- 
ment are seen by the use of the apparatus shown 
in Fig. 394. When the positive and negative 




Fig: 394» Effects of Molecular Bombardment. 

terminals are arranged as shown, the paths of the 
molecular slreams are seen as luminous streams 
whose directions are those shown in the figures. 

The figure on the left shows the path taken in 
a low vacuum. Streams pass from the negative 
electrode to each of the positive, electrodes. 

The figure on the right shows the discharge in 
a high vacuum. Here the streams pass off at 
right angles to the lace of the negative electrode, 



and. proceed therefrom in straight lines, inde- 
pendently of the position of the positive electrode. 
Since, therefore, the negative electrode at a, is in 
the shape of a concave mirror, the luminous 
particles converge to a focus near the centre of 
tue glass vessel, and then diverge to the opposite 
wall. 

Refractory substances placed at such a focus of 
molecular bombardment, as shown in Fig. 395, are 
rendered incandescent. 

In a similar manner, phosphorescent substances 
exposed to such molecular streams emit a beauti- 




Fig. 393. Forces of Molecular Bombardment. 

ful phosphorescent light. (See Phosphorescence, 
Electric.) 

Matter, Thomson's Hypothesis of 



A hypothesis as to the structure of matter 
suggested by Sir William Thomson, in order 
to show how the extremely tenuous ether 
might possess rigidity. 

The fact that the ether, although a fluid sub- 
s'ance, possesses the properties of a rigid solid, 
has given no little trouble to physicists. Thomson 
explains this rigidity of the ether as being due to 
a rapid motion in its fluid particles. 

A perfecdy flexible rubber tube filled with 
water or other fluid, possesses, when at rest, a 
very great degree of flexibility. When in mo- 
tion, however, the tube becomes more and more 
rigid, as the flow increases in rapidity. Thom- 



Mat.] 



302 



[Med. 



son imagines the ether to be set in motion in 
minute vortex rings, and shows that a readily 
movable fluid body, like ether, once set in su.h 
motion should possess the properties of a solid. 
I.i a perfect fluid, such as ether, these vortex 
rings once formed, would be practically imperish- 
able or indestructible. 

Thomson regards the atoms of matter as con- 
sisting of such vortex rin^s. Vortex rings can be 
formed in the air by cutting a circuhr aperture 
in the end of a pasteb^arl box, and tapping 
sharply against the end of the box. In order to 
render the rings visible, the box may be previously 
filled with smoke. 

Vortex rings formed in smoky air differ from 
vortex rings ia the eth.r, in the face that air is 
not a perfect fluid, while ether is. Air vortex 
rings increase in size and decrease in energy. 
Vortex rings of the ether would not vary in size. 

According to Thomson's vortex theory of 
matter, the atoms of matter are the same as the 
ether which surrounds them. They cannot be 
produced in ether by any known way; therefore, 
they cannot be manufactured, or, as it were, 
created. Nor, on the other hand, can they be 
destroyed; in other words, they are indestruct- 
ible. They are elastic, capable of definite vibra- 
tions, possess all the properties of matter sav:, in 
the opinion of some, the very important prop- 
erty of gravitation. As Prof. Lodge points out, 
the fact that this property is not present should 
cause Sir William Thomson's theory of matter to 
be accepted with considerable hesitation. 

Matthiessen's Metre-Gramme Standard. 

— (See Metre-Gram7ne Standard, Matthies- 
sen's) 

Mattliiessen's Mile Standard. — (See Mile 
Standard, Matthiessen's) 

Matting", Invisible Electric Floor 

— A matting or other floor covering, provided 
with a series of electric contacts, which are 
closed by the passage of a person walking 
over them. 

This matting is provided as an adjunct to a 
system of burglar alarms. The electric bell or 
annunciator, connected with the different con- 
tacts, is disconnected during the day-time, or while 
the rooms are occupied. (See Alarm, Burglar. ) 

Maximum Magnetization. — (See Mag- 
netizaiion, Maximum) 



Mclntire's Parallel Sleeve Telegraphic 
Joint. — (See [oint, Telegraphic, Mclntire's 
Parallel Sleeved) 

Measurements, Electric —Deter- 
minations of the values of the electromotive 
force, resistance, current, capacity, energy, 
etc., in any electric circuit. 

Electric measurements may be either qualitative 
or quantitative. 

In qualita ive electric measurements the rela- 
tive values only are obtained; in quantitative 
measurements the actual values are obtained. 

Mechanical Alarm, Electric (See 

Alar 7n, Electro-M echanical.) 

Mechanical Electric Bell. — (See Bell r 
Electro-Mechanical) 

Mechanical Equivalent of Heat. — (See 
Heat, Mechanical Equivalent of.) 

Mechanical Mine. — (See Mine, Mechani- 
cal.) 

Mechanical Throwback Indicator. — 
(See Indicator, Mechanical Throwback) 

Medical Induction Coil. — (See Coil, In- 
duction Medical) 

Medical Magneto-Electric Apparatus. — 
(See Apparatus, Magneto-Electric Medi- 
cal) 

Medium, Anisotropic A medium 

in which equal stresses do not produce equal 
strains when applied in different directions. 

A medium, homogeneous in structure like 
crystalline bodies, but possessing different 
powers of specific inductive capacity in differ- 
ent directions. 

An eolotropic medium. (See Mediwn, 
Eoloiropic) 

The latter term is used to distinguish it from 
an isotropic medium. (See M.dium, Isotropic.) 

Medium, Eolotropic A medium 

in which equal stresses do not produce the 
same strains when applied in different direc- 
tions. (See Medium, Isotropic) 

Medium, Electro-Magnetic ■ — Any 

medium in which electro-magnetic phenom- 
ena occur. 

The medium through which electro -magnetic 
waves are propagated is now universally re- 



Med.] 



363 



[Met. 



garded as the luminiferous or universal ether. 
(See Electricity ', Hertz's Theory of Electro-Mag- 
netic Radiations or Waves.) 

Medium, Isotropic A medium in 

which equal stresses applied in any direction 
produce equal strains. 

A transparent medium which possesses the 
same optical or electric properties in all di- 
rections. 

An optically homogeneous, transparent 
medium. 

Such media are called isotropic to distinguish 
them from anisotropic or eolotropic, or those in 
which equal stresses produce unequal strains in 
different directions. (See Medium, Anisotropic. 
Medium, Eolotropic.) 

Meg or Mega (as a prefix).— 1,000,000 
times ; as, megohm, 1,000,000 ohms ; mega- 
volt, 1 ,000,000 volts. 

— An appara- 



Megaloscope, Electric — 

tus for the medical exploration of the cavities 
of the body. 

The light necessary for exploration is obtained 
from a small incandescent lamp placed at the 
extremity of a tube, suitably shaped for introduc- 
tion into the special organ for which it is devised. 
The organ so illumined throws its light on a 
prism, by means of which the light is caused to 
pass through a series of lenses by which it is 
viewed. 

Megavolt. — 1,000,000 volts. 

Megohm. — 1, 000,000 ohms. 

Meidinger Yoltaic Cell.— (See Cell, Vol- 
taic, Meidinger) 

Memory, Magnetic A term pro- 
posed by J. A. Fleming for coercive force. 

Soft iron has but a feeble memory of its past 
magnetization. 

Mercurial Connection. — (See Connection, 
Mercuriafy 

Mercurial Contact. — (See Connection, 
Mercurial?) 

Mercurial Temperature Alarm. — (See 
Alarm, Mercurial Temperature) 

Mercury Break. — (See Break, Mercury) 

Mercury Cup. — (See Cup, Mercury) 



Meridian, Astronomical A great 

circle passing through any point in the 
heavens, and the North and South poles of 
the heavens. 

The astronomical meridian corresponds to the 
geographical meridian. The former is considered 
as passing around the dome of the heavens; the 
latter, around the surface of the earth. In order 
to locate any point in the heavens, a great circle 
of the heavens is caused to pass through that point 
and through the astronomical North and South 
poles. 

Meridian, Geographical The geo- 
graphical meridian of a place is a great circle 
passing through that place and the North and 
South geographical poles of the earth. 

Meridian, Magnetic The magnetic 

meridian of any place is the meridian which 
passes through the poles of a magnetic needle 
at that place when in a position of rest under 
the free influence of the earth's magnetism. 

The plane of the magnetic meridian at any place 
is a vertical plane pa-sing through the poles of a 
magnetic needle in a position of rest under the 
free influence of the earth's magnetism at that 
place. 

The magnetic meridian may be regarded as the 
vertical plane in which a freely suspended mag- 
netic needle comes to rest in the earth's magnetic 
field. 

Meridional. — Pertaining to the meridian. 

Message Wire.— (See Wire, Message) 

Messenger Call. — (See Call, Messenger.) 

Metallic Arc— (See Arc, Metallic.) 

Metallic Circuit.— (See Circuit, Metal- 
lic) 

Metallic Coating. — (See Coating, Metal- 
lic) 

Metallic Conducting Joint. — ^See/oinl, 
Metallic Conducting.) 

Metallic Contact.— (See Cojitact, Metal- 
lic) 

Metallic Electric Conduction. — (See 
Conduction, Electric, Metallic) 

Metallization. — The rendering of a non- 
conducting surface electrically conducting by 
covering it with a metallic coating, so as to 



Met.] 



364 



[Met. 



enable it to readily receive a metallic coating 
by electro-plating. (See Plating, Electro?) 

Metallochromes. — A name sometimes 
given to Nobili's rings. (See Rings, No- 
dili's.) 

Metalloid. — A name formerly applied to a 
non-metallic body, or to a body having only 
some of the properties of a metal, as carbon, 
boron, oxygen, etc. 

The term is now but little used. 

That branch 



Metallurgy, Electro — 

of applied science which relates to the elec- 
trical reduction or treatment of metals. 

Metallurgical processes effected by the 
agency of electricity. 

Electro-Metallurgy embraces : 

(i.) The reduction of metals from their ores, 
either directly during fusion by the heat of the 
voltaic arc, or the heat of incandescence, or by 
the electrolysis of solutions of their ores, or ores 
in the fused state. (See Electrolysis. Furnace, 
Electric.) 

(2.) Electroplating. 

(3.) Electrotyping. 

The application of electricity to the reduction 
of metals is carried on in the electric furnace for 
the reduction of the aluminium ores, ior example. 

Metals, Electric Deflagration of 

The volatilization of metals by electric in- 
candescence. 
Metals, Electric Keflning of 

Purifying metals by means of electricity. 

Different methods are employed for the electric 
refining of metals. They are generally electro- 
lytic in character. 

Metals, Electrical Protection of 

The protection of a metal from corrosion by 
placing it in connection with another metal, 
which, when exposed to the corroding liquid, 
vapor or gas, will form with the metal to be 
protected the positive element of a voltaic 
couple. 

The negative element of a voltaic couple is 
protected by the presence of the positive element, 
which is alone corroded. This method has been 
adopted with considerable success to electrically 
protect metals from corrosion. 

The following are examples of this protection : 
(1.) Davy proposed to protect the copper 



sheathing of ships from corrosion by attaching 
pieces of zinc to the copper sheathing. This 
succeeded too well, since the copper salts which 
were formerly produced, and acted as a poison 
to the marine plants and animals, being now 
absent, permitted these organisms to thrive to 
such an extent as to seriously foul the ship's 
bottom. 

(2.) A ring of zinc attached to a lightning rod, 
near its points, has, it is claimed, the power of 
protecting the points from corrosion. 

(3.) Iron bars of railings, if sunk or embedded 
in zinc, are preserved from corrosion near the 
junction of the two metals, but if sunk in lead are 
rapidly corroded, because iron is electro-positive 
to lead, but electro-negative to zinc. 

(4.) Tinned iron rapidly corrodes or rusts 
when the iron is exposed to the atmosphere by a 
scratch or abrasion, because the iron is electro- 
positive to tin. Nickel-plated iron, for the same 
reason, rusts rapidly on the exposure of an 
abraded surface. 

(5.) Zinced or galvanized iron, or iron covered 
with a deposit of zinc, is protected from corro- 
sion because the zinc, being positive to iron, can 
alone be corroded, and the zinc is also protected 
in part by the coating of insoluble oxide that is 
formed. 

Meteorites. — Aerolites. (See Aerolites?) 

Meter, Ampere — (See Ampere- 
Meter. A?nmeter?) 

Meter, Current A term now ap- 
plied to an electric meter or galvanometer 
which measures the current in amperes, as 
distinguished from one which measures the 
energy in watts. 

This term is sometimes loosely applied to a 
galvanometer. 

The term galvanometer is preferable. (See 
Galvanometer.) 

Meter, Current, Magneto-Static A 

current meter in which a small steel magnet, 
or system of magnets, is suspended at the 
centre of the uniform magnetic field produced 
by the combined influence of two coils and 
two systems of powerful permanent magnets. 

Meter, Electric — Any apparatus for 

measuring commercially the quantity of elec- 
tricity that passes in a given time through 
any consumption circuit. 



Met] 



365 



[Met. 



Electric meters are constructed in a great 
variety of forms; they may, however, be ar- 
ranged under the following heads : 

(I. ) Electro-Magtietic Meters, or those in which 
the current passing is measured by the electro- 
magnetic effects it produces. 

In such meters the entire current may pass 
through the meter. 

(2.) Electro-Chemical Meters, or those in which 
the current passing is measured by the electroly- 
tic decomposition it effects. 

In these meters, a shunted portion only of the 
current is usually passed through a solution of a 
metallic salt, and the current strength calculated 
.from the amount of electrolytic decomposition 
thus effected. 

(3.) Electro- Thermal Meters, or those in which 
the current passing is measured by a movement 
effected by the increase in temperature of a resist- 
ance through which the current is passed, or by 
the amount of a liquid evaporated by the heat 
generated by the current. 

(4.) Electric-Time Meters ; or those in which 
no attempt is made to measure the current that 
passes, but in which a record is kept of the num- 
ber of hours that an electric lamp, motor or 
other electro-receptive device is supplied with 
current. 

Edison's electric meter is of the second class. 
It consists of two voltameters, or electrolytic cells, 
containing zinc sulphate, in which two plates of 
chemically pure zinc are dipped. The current 
that passes is determined by the amount of the 
variation in weight of the zinc plates. To deter- 
mine this, the plates are weighed, at stated in- 
tervals : one plate every month, the other plate, 
which is intended to act as a check on the first, 
only once in three months. Some difficulty has 
been experienced in the employment of meters of 
this class, from the variations in the value of the 
shunt resistance, due to variations in the condi- 
tion and temperature of the electrolytic cell. 
The use of a compensating resistance, however, 
has, it is claimed, removed this objection. (See 
Voltameter. ) 

Meter, Electric-Time An electric 

meter in which the current passing is esti- 
mated by recording the number of hours that 
an electric lamp or other electro-receptive 
device is supplied with a known current. 
-(See Meter, Electric) 



Meter, Electro-Clieinical 



-An elec- 



tric meter in which the current passing is 
measured by the electrolytic decomposition it 
effects. (See Meter, Electric?) 

Meter, Electro-Magnetic An elec- 
tric meter in which the current passing is 
measured by the electro-magnetic effects it 
produces. (See Meter, Electric.) 

Meter, Electro-Thermal An elec- 
tric meter in which the current passing is 
measured by means of the heat generated by 
the passage of the current through a resist- 
ance. (See Meter, Electric) 

Meter, Energy A term sometimes 

applied to a watt meter. (See Meter, 
Watt) 

Meter, Milli- Ampere An ampere 

meter graduated to read milli-amperes. 

Meter, Watt An instrument gener- 
ally consisting of a galvanometer constructed 
so as to measure directly the product of the 
current, and the difference of potential. 

Since the watt is equal to the product of the 




Fig. 3Q6. Watt Meter. 

current by the electromotive force, if the current 
and electromotive force are simultaneously meas- 
ured, their product gives direcdy the watts. 
The scale reading of a watt meter may be grad- 
uated so as to give the watts directly. 

A watt meter consists essentially of a thick wire 
coil, placed in series in the circuit whose electric 
power is to be measured, and a thin wire coil 



Met.] 



366 



|Mic. 



placed in a shunt around the circuit to be meas- 
ured. These two coils, instead of acting on a 
needle, act on each other, and the amount of this 
deflection will, therefore, be proportional to the 
watts present. 
A form of watt meter is shown in Fig. 396. 

Method, Deflection A method em- 
ployed in electrical measurements, as distin- 
guished from the zero method, in which a 
deflection, produced on any instrument by a 
given current, or by a given charge, is utilized 
for determining the value of that current or 
charge. 

The conditions remaining the same, the same 
Current or charge will produce the same deflection 
at any time. Different deflections produced by 
currents or charges, the values of which are un- 
known, are determined by certain ratios existing 
between the deflections and the currents or 
charges. These ratios are determined experi- 
mentally by the calibration of the instrument. 
(See Calibrate.) 

Deflection methods are opposed to zero or null 
methods, in which latter a balance of opposite 
electromotive forces, or a proportionally equal 
fall of electric potential, is ascertained by the 
failure of a delicately poised needle to be moved 
by a current or a charge. 

Method, Null or Zero Any method 

employed in electrical measurements, in which 
the values of the electromotive force in volts, 
the resistance in ohms, or the current in am- 
peres, or other similar units, are determined 
by balancing them against equal values of the 
same units, and ascertaining such equality, not 
by the deflections of the needle of a galvano- 
meter, or of an electrometer, but by the ab- 
sence of such deflections. 

The advantage of zero methods is iound in the 
fact that the galvanometer or electrometer may 
then be made as sensitive as possible, which is not 
otherwise the case, since great deflections are 
generally to be avoided, especially in tangent 
galvanometers. (See Galvanometer. Electrom- 
eter.) 

Method of Magnetization by Touch. — 

(See Magnetization by Touchy 

Methven's Screen. — (See Screen, Meth- 
veris.) 



Metre Bridge.— (See Bridge, Metre) 
Metre Candle.— (See Candle, Metre) 
Metre-Gramme Standard, Matthiessen's 

A unit of resistance. 

The resistance of a wire one metre in. 
length, and of such a diameter as would cause 
the wire to weigh one gramme. 

One metre-gramme of pure hard drawn cop per 
has a resistance of .1469 B. A. units at zero de- 
grees C. as determined by Matthiessen {Phil. 
Mag., May, 1865). 

Metre-Millimetre A resistance unit 

of length of a wire or other conductor of the 
length of one metre and of the area of cross- 
section of one square millimetre. 

According to the report of the Committee of the 
American Institute of Electrical Engineers of 1890, 
on a Standard Wiring Table, a metre millimetre 
of pure soft copper wire has a resistance of .02057" 
B. A. units at zero degrees C. From the corre- 
sponding term, milfoot, millimetre-metre would 
appear to be the preferable term. 

Metric Horse-Power. — (See Horse-Power, 
Metric) 

Metric System of Weights and Meas- 
ures. — (See Weights and Measures, Metric 
System of.) 

Mho. — A term proposed by Sir Wm. 
Thomson for the practical unit of conductiv- 
ity. 

Such a unit of conductivity as is equal to 
the reciprocal of 1 ohm. 

The conducting power is equal to _ or the 

R 

reciprocal of the resistance. 

The word mho , as is evident, is obtained by in- 
verting the order of sequence of the letters in the 
word ohm. 

Mica. — A mineral substance employed as 
an insulator. 

Mica is a silicious mineral. It occurs of vary- 
ing degrees of transparency, and splits or cleaves 
readily into transparent laminae. It is a good 
nonconductor, is fairly fire proof, and is not 
hydroscopic. 

Mica is used extensively in insulating the me- 
tallic segment of commutators of motors and 
dynamo-electric machines and in various other 
electric work. 



Mic] 



36? 



[Mil. 



Mica, Moulded An insulating sub- 
stance consisting of finely divided mica made 
into a paste, with some fused insulating 
substance, and moulded into any desired 
shape. 

Finely divided mica mixed with gum-shellac 
rendered plastic by means of heat, forms a good 
insulating substance. 

Micro (as a prefix). — The one-millionth; 
as, a microfarad, the millionth of a farad ; a 
microvolt, the one-millionth of a volt. 

Micro-Farad. — (See Farad, Micro) 

Micro-Graphophone. — A modified form of 
phonograph in which several independent 
non-metallic diaphragms are used instead of 
the single diaphragm of the phonograph. (See 
Graphophonc, Micro) 

Micrometer, Arc An apparatus for 

the accurate measurement of the length of a 
voltaic arc by means of a micrometer. 

The distance between two carbon electrodes — 
one movable and the other fixed — placed inside a 
glass vessel, is accurately determined by means of 
a micrometer placed on the movable electrode. 
The operation is similar to that of the vernier 
■wire gauge. 

Micrometer, Spark A term some- 
times applied to Hertz's electric resonator. 
(See Resonator, Electric.) 

Micron. — A measure of length. 

The one-millionth part of a metre. 

The micron is equal to .00004 °f an inch, very 
nearly. 

Microphone. — An apparatus invented by 
Prof. Hughes for rendering faint or distant 
sounds distinctly audible. 

The microphone depends for its operation on 
variations produced in the resistance of the circuit 
of a battery, or other electric source, by means of 
a loose contact. These variations in the resist- 
ance are caused to produce corresponding move- 
ments in the diaphragm of a receiving telephone. 

The loose contact may take a variety of forms. 
Originally it was made in the form shown in Fig. 
397, in which a small piece of carbon E, pointed 
at both ends, is inserted in holes near the ends of 
cross-pieces of carbon B and C. The thin upright 
board A, on which these are supported, acts as a 



sounding board or diaphragm, and its movements 
by sound waves are at once audible to a person 
listening at the receiving telephone. The walk- 
ing of a fly over the sounding board is heard as a 
loud sound. 

The forms of transmitting telephones invented 
by Reis, Edison, Blake, Berliner and others, are 
in reality varieties of microphones. 




Fig. 3Q7. Microphone. 

Microphone Relay. — (See Relay, Micro- 
phone) 

Micro-Seismograph. — (See Seismograph, 
Micro.) 

Microtasimeter. — An apparatus invented 
by Edison to measure minute differences of 
temperature, or of moisture, by the resulting 
differences of pressure. 

A change of temperature, or moisture, is caused 
to produce variations in the resistance of a button 
of compressed lampblack, placed in the circuit, of 
a delicate galvanometer. The apparatus, though 
of surprising delicacy, is scarcely capable of prac- 
tical application, from the fact that the resistance 
of the carbon does not resume its normal value on 
the removal of the pressure. 

Miero-Yolt.— (See Volt, Micro) 

Mil.— A unit of length equal to the nnnr of 
an inch, or .001 inch, used in measuring the 
diameter of wires. 

Mil, Circular A unit of area em- 
ployed in measuring the areas of cross-sec- 
tions of wires, equal to .78540 square mil. 

The area of a circle one mil in diameter. 



Mil.] 



368 



[Min. 



One circular mil equals .000000785 square inch. 

The area of cross-section of a circular wire in 
circular mils is equal to the square of its diameter 
expressed in mils. (See Units, Circular.) 

Mil-Foot. — A resistance unit of length of 
one foot of wire or other conductor of one 
mil diameter. 

The resistance of a mil-foot of soft copper wire 
or wire 1 foot long and .001 of an inch in diam- 
eter is equal to 9.720 B. A. units at O degrees C. 

Mil, Square A unit of area em- 
ployed in measuring the areas of cross-sec- 
tions of wires, equal to .000001 square inch. 

One square mil equals 1.2732 circular mil. 

Mile, Nautical A knot, or a dis- 
tance of 6,087 feet, or very nearly 1.15 statute 
miles. 



The 



of the earth's equatorial 



cumference, or the -fa of a degree of longi- 
tude at the equator, or about 2,029 yards. 

A nautical or geographical mile bring the 
¥t!o¥ °f 2 4>^99 miles, has a value somewhat 
greater than that of the statute mile. 

Mile Standard, Matthiessen's A 

standard of resistance equal to the resistance 
of one mile of pure copper wire -fa inch in 
diameter at 15.5 degrees C. 

Matthiessen's mile standard has a resistance of 
13.59 B- A units at 15 5 degrees C. 

Mile, Statute The ordinary unit of 

distance on land, equal to 5,280 feet. 

Milli (as a prefix).— The one-thousandth 
part. 

Milli- Ampere. — The thousandth of an am- 
pere. 

Milli-Calorie. — The smaller calorie. (See 
Calorie, Small.) 

Milli-Oerstedt. — The one-thousandth of 
an Oerstedt. 

Mimosa Sensitiva. — A sensitive plant 
whose leaves fold or shut up when touched. 

The fibres of all the sensitive plants, such, for 
example, as the above, the Venus' Fly-trap, etc., 
like all muscular fibre, and indeed all protoplasm, 
suffer contraction when traversed by electric cur- 
lents. 

Mine, Electro-Contact — A sub- 
marine mine that is fired automatically on 
the completion of the current of a battery 



placed on the shore through the closing of 
floating contact points by passing vessels. 
(See Mine, Submarine) 
Mine Exploder, Electro-Magnetic 

A form of electro-magnetic exploder. (See 
Exploder, Electro-Magnetic) 

Mine, Mechanical A submarine 

mine that is fired when struck by a passing 
ship by the action of some contrivance con- 
tained within the torpedo itself, and having 
no connection whatever with the shore. 

Mine, Observation A variety of 

submarine mine that is fired when the 
enemy's vessels are observed to be within the 
destructive area of the mine. (See Mine, 
Submarine.) 

Various means are adopted for obtaining the 
current required for firing such mines. A suffi- 
ciently powerful battery is generally used. An 
electro-magnetic mine exploder may, under cer- 
tain circumstances, be employed. (See Mine 
Exploder, Electro -Magnetic. ) 

Mine, Submarine A mass of gun- 
cotton or other explosive contained in a 
water-tight vessel and placed under water so 
as to be exploded on the passage over it of 
an enemy's vessel. 

A submarine mine is a stationary torpedo ar- 
ranged for the defense of a harbor. A harbor 
is protected by a number of mines which are so 
arranged as to be readily exploded by the passage 
of an enemy's ship, but safely crossed by other 
vessels. 

Submarine mines consist essentially of gun- 
cotton or other explosives contained in water-tight 
vesse'is anchored in very carefully located posi- 
tions, and connected with the shore by means of 
cables. 

An operating-room at the shore end of the 
cable is furnished with batteries, measuring in- 
struments, contact keys, etc., etc., by means of 
which the mines can be exploded by the trans- 
mission of an electric current through the cables; 
or, the mines are furnished with automatic cir- 
cuit closers in which two central points are closed 
by the passage of the vessel. In ordinary times 
this current is too weak to ignite the fuse, and 
merely closes a relay in the operating room, 
which in turn directs a current through a bell or 
indicator, but, of course, too weak to fire the fuse. 



Min.] 



309 



[Mom. 



In times of war, however, the relay sends a 
current through the cable sufficiently strong to 
heat a platinum iridium fuse, ignite a fulminate of 
mercury cap, and thus, by the detonation of the 
primer of dry gun-cotton, explode the full charge 
of damp gun-cotton in the torpedo or mine. 

Mine, Subterranean A mass of 

gun powder, gun-cotton or other explosive, 
placed under ground in vessels suitable for 
protection against moisture, and fitted with 
electrically connected electric fuses, which are 
either exploded automatically by the move- 
ment of an enemy over them, or by an oper- 
ator placed at a safe distance within an en- 
trenchment. 

Minute, Ampere One ampere flow- 
ing for one minute. (See Hour, Ampere?) 

Minute, Watt A unit of electrical 

work. 

The expenditure of an electrical power of 
one watt for one minute. 

The watt-minute is equal to 60 joules. This 
unit of electrical work is seldom used. 

Miophone. — An apparatus invented by 
Boudet based on the use of the microphone, 
and designed for the medical examination of 
the muscles. 

Mirror Galvanometer.— (See Galvanom- 
eter, Mirror?) 

Moist Electrode.— (See Electrode, Moist.) 
Moisture, Effect of, on Electrical Phe- 
nomena — The influence of moisture 

on the surfaces of insulators in causing the 
loss or dissipation of an electric charge. 

This loss is more rapid with negatively charged 
bodies than with those positively charged. 

Molar Attraction. — (See Attraction, 
Molar?) 

Molecular.— Pertaining to the molecule. 
(See Molecule^ 

Molecular Attraction.— (See Attraction, 
Molecular?) 

Molecular Bombardment— (See Bom- 
bardment, Molecular?) 

Molecular Chain.— (See Chain, Molecu- 
lar?) 



Molecular Currents.— (See Currents, 
Molecular or Atomic?) 

Molecular Currents, Induced (See 

Currents, Induced Molecular or Atomic?) 

Molecular Range. — (See Range, Molecu- 
lar?) 

Molecular Repulsion. — (See Repulsion 
Molecular?) 

Molecular Rigidity. — (See Rigidity, 
Molecular?) 

Molecular Theory of Muscle and Nerve 
Currents. — (See Theory, Molecular, of Mus- 
cle and Nerve Currents?) 

Molecule. — A group of atoms whose 
chemical bonds or affinities are mutually 
satisfied. 

The smallest quantity of a compound sub- 
stance that can exist as such. 

Water is a compound substance formed of two 
atoms of hydrogen combined with one atom of 
oxygen. The molecule of water, therefore, or 
the smallest quantity of water that can exist, must 
contain two atoms of hydrogen and one of oxygen. 

The molecule of hydrogen consists of two atoms 
of hydrogen. Since hydrogen is a monad, or an 
element whose atomicity is one, it can combine 
with one atom of hydrogen and fcrm a molecule, 
since then its bonds will be fully satisfied. (See 
Atomicity.) 

Molecule, Closed-Magnetic Circuit of 

— (See Circuit, Closed-Magnetic, of 

Molecule?) 

Molecule, Gramme The weight of 

any substance taken in grammes numerically 
equal to the molecular weight. 

Moment, Magnetic The sum of the 

two forces of the directive couple multiplLd 
by half the perpendicular distance between the 
directions of these forces ; or, in other words, 
the moment of a magnet is equal to its length 
multiplied by the intensity of the magnetism 
of one of its poles. (See Couple, Magnetic.) 

Moment of Couples.— (See Couple, Mo- 
ment of.) 

Momentary Current.— (See Current, Mo- 
mentary?) 

Momentum, Electro-Magnetic, of Sec- 
ondary Circuit A quantity equal to 



Mon.] 



370 



[Mot. 



the co-efficient of mutual induction, multi- 
plied by the current strength in the primary, 
when the primary current is fully established. 
When the primary current is fully established, 
the number of lines of force which pass through 
the secondary circuit is equal to the co-efficient of 
mutual induction, multiplied by the strength of 
the primary current. 

Monophotal Arc-Light Regulator. — (See 
Regulator, Monophotal Arc-Light?) 
Mordey Effect.— (See Effect, Mordey) 
Morse Alphabet. — (See Alphabet, Tele- 
graphic : Morse's?) 

Morse Inker. — (See Inker, Morse.) 
Morse Recorder. — (See Recorder, Morse?) 
Morse Register. — (See Register, Morse) 
Morse System of Telegraphy. — (See 
Telegraphy, Morse System of.) 

Morse's Telegraphic Alphabet. — (See Al- 
phabet, Telegraphic : Morse's?) 

Morse's Telegraphic Sounder. — (See 
Sounder, Morse's Telegraphic.) 

Motion, Energy of A term some- 
times applied to actual or kinetic energy in 
contradistinction to potential energy. (See 
Energy, Actual?) 

Motion, Simple-Harmonic Motion 

which repeats itself at regular intervals, taking 
place backwards or forwards, and which may- 
be studied by comparison with uniform mo- 
tion round a circle of reference. — {Daniell.) 



F 


E 

/ 


[ 


) ! 


\ ( 


-v 


3 



Fig. 398. Shitple-Harmonic Motion. 

Motion which is a simple periodic function 
of the time. 

Suppose a pendulum be set swinging in a cer- 
tain path. If the path of such a pendulum, or, 
as it is generally called, a conical pendulum, be 



looked at from above or from below, it will appear 
to be circular; if observed from one side it will 
appear elliptical, and this elliptical path will ap- 
pear longer and narrower as the eye of the ob- 
server approaches the level of the plane in which 
the bob moves, when the bob will appear to 
travel backwards and forwards in a straight line. 
The bob will appear to be moving faster, when it 
is moving right across the field of view. 

Let the circle QCR (Fig. 398) be ihe path in 
which the bob moves, and let Q A, A B, B C, C o, 
etc., be equal distances in such path. Let the 
lines A a, B b, C c, o O, etc., be drawn perpendicu- 
lar to the line Q R. Then when looked at, with 
the eye on the level of the plane in which the bob 
travels, the line Q R, will be the path in which 
the bob appears to move backwards and for- 
wards, and the lines, Qa,ab, be, cO, etc., will 
represent the spaces apparently traversed in 
equal intervals of time. 

The circle Q o R, is called the circle of refer- 
ence. 

Motion, Simple-Harmonic, Amplitude of 

The length of the swing fiom the 

median position to its extreme position, in 
either direction. 

The line O Q, or O R, in the circle of reference 
QOR (Fig. 398). 

Motion, Simple-Harmonic, Negative Di- 
rection of The motion which a body, 

with a simple-harmonic motion, has when it 
appears to move from left to right. 

Motion, Simple-Harmonic, Period of 

— The interval of time which elapses between 
two successive passages of a moving particle, 
over the same point, in the same direction. 

The period of simple-harmonic motion repre- 
sents the time of one complete motion around a 
circle called the circle of reference. (See Motion, 
Simple -Harmonic. ) 

Motion, Simple-Harmonic, Phase of 

— The position of a point executing a simple 
harmonic motion, expressed in terms of Lie 
interval of time which has elapsed since 
such point last passed through the middle 
of its path in the positive direction. — (An- 
thony &* Brackett.) 

The exact position of a particle executing a 
simple-harmonic motion for any instant of time 
can be readily expressed in terms of the phase. 



Mot] 



371 



[Mot. 



Motion, Simple-Harmonic, Positive 

Direction of The motion which a 

body moving in simple-harmonic motion has, 
when it appears to move from right to left. 

Motion, Simple-Periodic A term 

sometimes employed in the sense of simple- 
harmonic motion. (See Motion, Simple- 
^Harmonic.) 

Motion, Simple-Sine -A term some- 
times employed in the sense of simple-har- 
monic motion. (See Motion, Simple-Har- 
monic?) 

Motograph, Electro — An apparatus 

invented by Edison whereby the friction of a 
platinum point against a rotating cylinder of 
moist chalk, is reduced by the passage of 
an electric current. 

This result is due to electrolytic action at the 
points of contact, varying the friction. 

The electro-motograph, though less certain in 
its action than an electro-magnet, may replace it 
in certain electric apparatus. 

The detailed construction of the electro moto- 
graph will be understood from an inspection of 
Tig- 399- 

The lever A, pivoted with a universal joint at 
C, has a metallic point at its free extremity F, 
resting on a strip of moistened paper N, and held 
against it with some pressure by the action of the 
spring S. The paper N, rests on the metallic 
drum G, over which it is moved on the rotation 
of the drum by clockwork. A spring R, acts to 
move the lever A, in a direction opposite to that 
in whii h it tends to move by the rotation of the 
drum G. 

The main battery L, is connected at i^s negative 
pole to the point F, and at its positive pole, through 
the key K, to the metallic drum G. The local bat- 
tel y L B, is connected through the sounder X, to 
the contacts D and X. 

Waen the key K, is open, the friction of F, on 
the paper N, is sufficient to move the lever A, t > 
the right so as to close the circuit of the local 
battery, but when the key K, is depressed, the 
current of L, passing through the paper, decom- 
poses the chemicals with which it is moistened, 
lessens the friction of the point F, and permits the 
spring B, to draw the lever A, to the left, thus 
opening the circuit of the local battery L B. 

The movements of the key are therefore repro- 
duced by the armature of the electro-magnet X. 



An excellent loud speaking telephone has been 
devised by Edison on the principle of the electro- 
motograph. 




Fig. 3QQ. Electro-Motograph. 

Motor, Compound-Wound An elec- 
tric motor whose field magnets are excited by 
a series and a shunt wire. (See Machine, 
Dynamo-Electric , Co?npound- Wound.) 

Motor, Differentially Wound A 

compound-wound motor, in which the cur- 
rent in the shunt coils opposes in its magnet- 
izing effects the current in a series coil, so 
that the efficient magnetizing effect produced 
is the difference in the magnetizing effect of 
the two coils. 

Motor, Electric A device for trans- 
forming electric power into mechanical 
power. 

All practical electric motors depend for their 
operation on the tendency to motion in a mag- 
netic field of a conductor canning a current or 
on magnetic attraction or repulsion. The entire 
magnetism may be produced by the current, or 
part may be obtained from permanent magnets, 
and the rest from electro-magnets. 

A dynamo-electric machine will act as a motor 
if a current is sent through it. Such a motor is 
sometimes caMed an electro motor. The term 
electric motor would, however, appear to be the 
preferable one. 

In all cases the rotation is in such a direction as 
to induce in the armature an electromotive force 
opposed to that of the driving current ; this is 
therefore called the counter electromotive force. 

A magneto-dynamo, or a dynamo the field of 
which is obtained from permanent magnets, or a 
separately excited dynamo, will operate as a 
motor when a current is sent through iis nraia 
ture, and will turn it in the opposite direction to 
that required to drive it in order to produce a 
current in the same directio ». 

A series dynamo will operate as a motor when 



Mot.] 



372 



[Mot. 



a current is sent through it. If the current is 
sent through it in the opposite direction to that 
which it produces when in operation as a gener- 
ator, the polarity of the field is reversed and the 
dynamo will turn as a motor in the opposite direc- 
tion to that required to produce the current. If 
the current is reversed, the polarity of both the 
field and the armature is again reversed, and the 
dynamo still rotates as a motor in the opposite 
directioii to that in which it is rotated as a 
generator. 

A series dynamo, therefore, always rotates as a 
motor in a direction opposite to that of its rotation 
as a generator. 

When, however, the polarity of the field only 
is reversed by changing the connection between 
the armature and the field, the rotation is in the 
same direction. 

A shunt dynamo operated as a motor will also 
turn in but one direction, but this direction is the 
same as that in which it turns when operating 
as a generator; for if the direction of the current 
in the armature is the same as in a generator, 
that in the shunt is reversed. 

A compound wound dynamo will move in a 
direction opposite to that of its motion as a gene- 
rator if the series part is more powerful than the 
shunt, and in the same direction if the shunt part 
is more powerful than the series. To use a com- 
pound-wound dynamo as a differential motor the 
connections need not be changed. For a cumu- 
lative motor it is necessary to reverse the connec- 
tions of the series coils. 

Alternating-Current Dynamo. — The current 
from an alternating-current dynamo, if sent 
through another similar alternating-current dy- 
namo running at the same speed, will drive it as a 
motor. Such a machine possesses the disadvan- 
tage of requiring to be maintained at a speed de- 
pending on that of the driving dynamo, and also 
that it requires to be brought to nearly this speed 
before the driving current is supplied to it. As a 
result of this last requirement, variations in the 
load are apt to stop the motor. Considerable 
improvements, however, are being introduced 
into alternate-current motors, by which these 
difficulties are almost entirely removed. 

An alternating current sent through any self- 
exciting dynamo electric machine, such as a 
shunt or series machine, will drive it continu- 
ously as a motor. The sudden reversals in the 
magnetization of its cores will, however, unless 
the cores are thoroughly laminated, set up power- 



ful eddy currents that will injuriously heat the 
machine, and there is also excessive sparking at 
the brushes. 

The reversibility of any dynamo -electric ma- 
chine, or its ability to operate as a motor if sup- 
plied with a current, leads to a fact of great 
importance in the efficiency of electric motors, 
viz. : that during rotation there is induced in the 
armature during its passage through the field of 
the machine, an electromotive force opposed co 
that produced in the armature by the driving 
current, or a counter electromotive force, (See 
Resistance, Spurious. ' Force, Counter Electro- 
motive.) This counter electromotive force acts 
as a spurious resistance, and opposes the passage 
of the driving current, so that, as the speed of the 
electric motor increases, the strength of the driv- 
ing current becomes less, until, when a certain 
maximum speed is reached, very little current 
passes. In actual practice, this maximum speed 
is not attained, or is only momentarily attained,, 
and a small, nearly constant, current is expended. 
in overcoming friction at the bearings, air fric- 
tion, etc. 

When, however, the load is placed on the 
motor, that is, when it is caused to do work, the 
speed is reduced and the counter electromotive- 
force is decreased, thus permitting a greater cur- 
rent to pass. The fact that the load thus auto- 
matically regulates the current required to drive 
the motor, renders electric motors very economi- 
cal in operation. 

The relations between the power required to 
drive the generating dynamo, and that produced 
by the electric motor, are such that the maximum 
work per second is done by the motor when it 
runs at such a rate that the counter electro- 
motive force it produces is half that op the current 
supplied to it. The maximum work or activity of 
an electric motor is therefore done when its theo- 
retical efficiency is only 50 per cent. This, 
however, must be carefully distinguished from 
the maximum efficiency of an electric motor. A 
maximum efficiency of 100 per cent, can be at- 
tained theoretically ; and, in actual practice, con- 
siderably over 90 per cent, is obtained. In such, 
cases, however, the motor is doing work at less 
than its maximum power. 

This is Jacobi's law of maximum effect, but 
does not apply to actual motors on account of the 
J imitations of current carrying capacity. Fcr 
example, a motor of 9 horse power and 90 per 
cent, efficiency loses 1 horse-power in heat within 



Mot.] 



373 



[Mot. 



itself. Hence, if run according to Jacobi's law, 
it would only produce the same amount, i. e., I 
horse-power in useful work instead of 9. More 
than this would overheat it. 

An efficiency of 100 per cent, is reached when 
the counter electromotive force of the motor is 
equal to that of the source supplying the driving 
current. Supposing now the driving machine to 
be of the same type as the motor, and the two 
machines are running at the same speed. If 
now a load is put on the motor so as to reduce its 
speed, and thus permit it to produce a counter 
electromotive force of but 90 per cent., its 
efficiency will be but 90 per cent. In such a 
case, therefore, the efficiency is represented by 
the relative speeds of the generator and the 
motor. 

Motor, Electric, Alternating-Current 

An electric motor driven or operated 

by means of alternating currents. (See 
Motor, Electric?) 

Dr. Louis Duncan divides alternating motors 
into two classes, viz. : 

(1.) Those in which there is but one trans- 
formation in the machine, viz., that of the electric 
energy of the armature current into the mechani- 
cal energy of the armature's rotation. 

(2.) Those in which there are two transforma- 
tions, viz.: 

(a.) The transformation of electrical energy 
from the main current to electrical energy in the 
armature current. 

(b.) The transformation of the electric energy 
of the armature current into mechanical energy. 

Alternating motors of the first type are found 
in the ordinary alternating-current dynamo re- 
versed. Those of the second type in Tesla's or 
Thomson's motors. 

Motor, Electric, Direct-Current 

An electric motor driven or operated by 
means of direct or continuous electric cur- 
rents, as distinguished from a motor driven 
or operated by alternating currents. '■- (See 
Motor, Electric?) 

Motor, Electric, High-Speed The 

ordinary electric motor. 

The term high-speed electric motor is used in 
contradistinction to low-speed electric motor. 
(See Motor, Electric, Low- Speed.) 

Motor, Electric, Low-Speed A 



slow-speed motor. (See Motor, Electric t 
Slow-Speedy 

Motor, Electric, Overload of A 

load greater than that which an electric motor 
can carry while at its greatest efficiency of 
operation, or a load which causes injurious 
heating of a motor. • 

Motor, Electric, Reversing Gear of 

— Apparatus for so reversing the direction of 
the current through an electric motor as to re- 
verse the direction of its rotation. (See Rail- 
road, Electric?) 

Motor, Electric, Slow-Speed An 

electric motor so constructed as to run with, 
fair efficiency at slow speed. 

The electric motor develops a counter electro- 
motive force when in motion, which, of course, 
increases with the increase of motion. The elec- 
tric motor has, as generally constructed, its great- 
est efficiency at high speed. When used on street 
railroads, the high speed requires to be decreased 
by various forms of reduction gear. The loss of 
power which all such gear involve, together with 
the noise attending their use, render any decrease 
in speed that can be obtained on the part of the 
motor, without serious loss of efficiency, desir- 
able. 

Motor-Electromotive Force. — (See Force, 
Motor Electromotive) 

Motor, Pyromagnetic A motor 

driven by the attraction of magnet poles on 
a movable core of iron or nickel unequally 
heated. 

The intensity of magnetization of iron decreases 
with an increase of temperature, iron losing most 
of its magnetization at a red heat. A disc of iron 
placed between the poles of a magnet, so as to 
be capable of rotation, will rotate, if heated at a 
part nearer one pole than the other, since it be- 
comes less powerfully magnetized at the heated 
part. 

In the form of pyromagnetic motor devised by 
Edison, and shown in Fig. 400, in elevation, and 
in Fig. 401, in vertical section, the disc of iron is 
replaced by a series of small iron tubes, or di- 
vided annular spaces, heated by the products of 
combustion from a fire placed beneath them. In 
order to render this heating local, a flat screen is 
placed dissymmetrically across the top to prevent 



Mot.] 



374 



[Mot, 



the passage of air through the portion of the iron 
tubes so screened. The air is supplied to the 
furnace by passing down from above through the 




Fig. 400. Pyromagnetic Motor. 

tubes so screened. This is shown in the draw- 
ings, the direction of the heating and the cooling 
air currents being indicated by the arrows. The 




Fig. 401. Pyromagnetic Motor. 

-supply of air from above thus insures the more 
rapid cooling of the screened portion of the 
tubes. 

Motor, Rotating-Current An 

electric motor designed for use with a rotat- 
ing electric current. 



Unlike alternating current motors, rotary -cur- 
rent motors will, like continuous-current motors, 
readily start with a load. (See Current, Rotating. ) 

Motor, Series-Wound An electric 

motor in which the field and armature are 
connected in series with the external circuit as 
in a series dynamo. (See Machine, Dynamo- 
Electric, Series- Wound) 

Motor, Shunt- Wound An electric 

motor in which the field magnet coils are 
placed in a shunt to the armature circuit. 
(See Machine, Dynamo-Electric, Shunt- 
Wound) 

Motor Standards. — (See Standards, 
Motor) 

Moulded Mica.— (See Mica, Moulded) 
Moulding, Electric Wood Mould- 
ing of dried, non-conducting wood, provided 
with longitudinal grooves for the reception 
and support of electric wires or conductors. 

Wood mouldings are employed for the protec- 
tion and concealment of electric conductors. 

Moulding Wiring. — (See Wiring, 
Moulding) 
Mouse-Mill 

Mouse-Mill) 
Mouse-Mill 

Mouse-Mill) 

Mouth Pieces. — (See Pieces, Mouth) 

Movable Secondary. — (See Secondary, 
Movable) 

Mover, Prime In a system of dis- 
tribution of power the motor by which sec- 
ondary motors or movers are driven. 

In a steam plant, the steam engine is the prime 
mover; the shafts or machines driven by the main 
shaft are sometimes called the secondary movers. 
The main shaft is called the driving shaft. Its 
motion s is carried by means of belts to other 
shafts, called driven shafts. The pulleys on the 
driving or driven shafts are called respectively 
the driving and driven pulleys. 

Movers, Secondary The shafts or 

machines driven by the main shafts in order 
to distinguish them from the steam engine or 
other mover which drives it. (See Mover, 
Prime) 



Dynamo. — (See Dynamo, 
Machine. — (See Machine, 



Mul.l 



375 



[Mul, 



Multi-Cellular Electrostatic Yoltmeter. 

— (See Voltmeter, Multi-Cellular Electro- 
static^) 

Multiphase Current— (See Current, Mul- 
tiphase?) 

Multiphase Dynamo. — (See Dynamo, 
Multiphase?) 

Multiphase System. — (See System, Multi- 
phase?) 

Multiple- Arc Circuit. — (See Circuit, 
Multiple- Arc?) 

Multiple- Arc-Connected Electro-Recep- 
tive Devices.— (See Devices, Electro-Recep- 
tive, Multiple-Arc-Connected) 

Multiple-Arc-Connected Sources. — (See 
Sources, Multiple- A re- Connected.) 

Multiple-Arc-Connected Translating" De- 
vices. — (See Devices, Translating, Mul- 
tiple-Arc-Connected.) 

Multiple-Brush Rocker. — (See Rocker, 
Multiple-Brush?) 

Multiple-Brush Yoke.— (See Yoke, Mul- 
tiple-Pair Brush?) 

Multiple Cable Core.— (See Cable, Mul- 
tiple-Core?) 

Multiple Circuit.— (See Circuit, Mul- 
tiple?) 

Multiple Conduit.— (See Conduit, Mul- 
tiple?) 

Multiple-Connected Battery.— (See Bat- 
tery, Multiple-Connected?) 

Multiple-Connected Electro-Receptive 

Devices.— (See Devices, Electro-Receptive, 
Multiple- Comiected.) 

Multiple-Connected Electro-Receptive 

Devices, Automatic Cut-Out for (See 

Cut-Out, Automatic, for Multiple-Connected 
Electro-Receptive Devices?) 

Multiple-Connected Translating" Devices. 
— (See Devices, Translating, Multiple-Con- 
nected.) 

Multiple Connection. -(See Connection, 
Multiple?) 



Multiple Distribution of Electricity by 
Constant Potential Circuits. — (See Elec- 
tricity, Multiple Distribution of, by Constant 
Potential Circuits?) 

Multiple Electric-Gaslighting. — (See 
Gaslighti?ig, Multiple Electric?) 

Multiple-Series. — A multiple connection 
of series groups. (See Connection, Series 
Multiple?) 

Usage in regard to this term is divided. By 
some the term multiple-series is applied to a series 
connection of parallel groups. This is done on 
account of the order of the words, multiple-series 
indicating, it is claimed, a series connection of 
multiple groups. 

Multiple-Series Circuit. — (See Circuit, 
Multiple- Series?) 

Multiple-Series-Connected Electro-Re- 
ceptive Devices. — (See Devices, Electro- 
Receptive, Multiple-Series-Connected?) 

Multiple - Series Connected Sources. — 

(See Sources, Multiple-Series-Comiected?) 

Multiple-Series-Connected Translating 
Devices. — (See Devices, Translati?ig, Mul- 
tiple- Series- Connected.) 

Multiple-Series Connection.— (See Con- 
nection, Multiple-Series.) 

Multiple-Switch Board. — (See Board, 
Multiple- Switch .) 

Multiple Transformer. — (See Trans- 
former, Multiple?) 

Multiple Transmission. — (See Trans- 
mission, Multiple?) 

Multiple Working of Dynamo-Electric 
Machines. — (See Working, Multiple, of 
Dynamo-Electric Machines?) 

Multiplex Telegraphy. — (See Teleg- 
raphy, Multiplex?) 

Multiplicator. — A word sometimes used 
for multiplier. 

Multiplier, Galvanic A term for- 
merly applied to a galvanometer. (See Gal- 
vanometer?) 

Multiplier, Schweigger's The 

name first given to a coil consisting of a 



Mul.] 



376 



[Nee. 



number of turns of insulated wire, provided 
for the purpose of increasing the strength of 
the magnetic field produced by an electric 
current, and consequently the amount of its 
deflecting power on a magnetic needle. 

Schweigger's multiplier was in fact an early 
form of galvanometer. (See Galvanometer.) 

Multiplying* Power of Shunt. — (See 
Shunt, Multiplying Power of) 

Multipolar Armature. — (See Armature, 
Multipolar.) 

Multipolar Dynamo-Electric Machine. — 
(See Machine, Dynamo-Electric, Multipo- 
lar.) 

Multipolar-Electric Bath. — (See Bath, 
Multipolar Electric.) 

Muscle Current. — (See Current, Muscle.) 

Muscles, Electrical Excitation of 

(See Excitation, Electro- Muscular) 



Muscular, Electro 



-Pertaining to 



the influence of electricity on the muscles. 

Muscular or Nerve Fibre, Excitability 

of (See Excitability, Electric, of 

Nerve or Muscular Fibre) 

Muscular Pile, Matteucci's (See 

Pile, Muscular, Matteucci's) 

Musket, Electric A gun in which 

the charge is ignited by a platinum wire ren- 
dered incandescent by the action of a bat- 
tery placed in the stock of the gun. 

Mutual Inductance. — (See Inductance) 

Mutual Induction. — (See Induction,. 

Mutual) 

Mutual Induction, Co-efficient of 

— (See Induction, Mutual, Co-efficient of) 

Myria (as a prefix). — A million times. 



N 



N. — A contraction employed in mathe- 
matical writings for the whole number of 
lines of magnetic force in any magnetic cir- 
cuit. 

N. — A contraction for North Pole. 

This N, may be distinguished from the N, used 
for expressing the whole number of lines of mag- 
netic force, by making the former light and the 
latter heavy. 

N. H. P. — A contraction for Nominal 
Horse-Power. 

Nominal horse-power is a somewhat indefi- 
nite term for a quantity dependent on the length 
of stroke and the dimensions of the cylin- 
der. This quantity is a dependent one, be- 
cause it varies necessarily with the type of en- 
gine. 

Nascent State. — (See State, Nascent) 

Natural Currents. — (See Currents, Nat- 
ural) 
Natural Law. — (See Law, Natural) 

Natural Magnet— (See Magnet, Nat- 
ural) 



Natural Unit of Electricity.— (See Elec- 
tricity, Natural Unit of) 
Natural Unit of Quantity of Electricity, 

— (See Electricity, Unit Quantity of, Natu- 
ral) 

Nautical Mile. — (See Mile, Nautical) 

Needle Annunciator. — (See An?iunciator r 
Needle.) 

Needle, Astatic A compound mag- 
netic needle of great sensibility, possessing 
little or no directive power. 

An astatic needle consisting of two separate 
magnetic needles, rigidly connected together 
and placed parallel and directly over each 
other, with opposite poles opposed. 

An astatic needle is shown in Fig. 402. The 
two magnets N S, and S' N', are directly opposed 
in their polarities, and are rigidly connected to- 
gether by means of the axis a, a. So disposed, 
the two magnets act as a very weak single needle 
when placed in a magnetic field. 

Were the two magnets N S, and S' N', of ex- 
actly equal strength, with their poles placed in 
exactly the same vertical plane, they would com- 
pletely neutralize each other, and the needle 



Nee.] 



377 



[Nee. 



would have no directive tendency. Such a sys- 
tem would form an Astatic Pair or Couple. 

In practice it is impossible to do this, so that the 




g-t- 



• 5 

Astatic Pair. 



Fig. 402. Asia t c Needle. 

needle has a directive tendency, which is often 
east and west. 

The cause of the east and west directive ten- 
dency of an unequally bal- 
anced astatic system will 
be understood from an in- \ 
spection of Fig. 403. Un- * - [g g 
less the two needles, N S, 
and S' N', are exactly op- 
posed, they will form a F*g' 403- 
single short magnet, N N N N, S S S S, the poles 
of which are on the sides of the needle. The 
system pointing with its sides due north and 
south will appear to have an east and west direc- 
tion. 

The principal use of the astatic needle is in the 
astatic galvanometer, in which the needle is de- 
flected by the passage of an electric current 
through a conductor placed near the needle. 
Therefore it is evident that one of the needles 
must be outside and the other inside the coil. In 
the most sensitive 
form of galvanome- 
ter there is also a 
coil surrounding the 
upper needle, the 
two coils being op- 
positely connected, 
so that the deflection 
on both needles is in 
the same direction, 
and the deflecting Fig. 404. Astatic System. 
power is equal to the sum of the two coils, while 
the directive power of the needles is the differ- 
ence of their magnetic intensities. 

In the astatic system, as shown in Fig. 404, the 
current, which flows above one needle, flows be- 
low the other, and therefore deflects both needles 




in the same direction, since their poles point in 
opposite directions. 

In some galvanometers a varying degree of 
sensitiveness is obtained by means of a magnet, 
called a compensating magnet, placed on an axis 
ab ive the magnetic needle. As the compensat- 
ing magnet is moved towards or away from the 
needle the effect of the earth's field is varied, and 
with it the sensitiveness of the galvanometer. 
Such a magnet may form with the needle an 
astatic system. (See Magnet, Compensating. 
Galvanometer, Astatic. Galvanometer, Mirror. 
Multiplier, Schweigger' 1 s) . 

Needle Electrode. — (See Electrode, Nee- 
dle^ 

Needle, Elongation of A phrase 

sometimes used for the angular deflection of 
a needle. 

Needle, Magnetic A straight bar- 
shaped needle of magnetized steel, poised 
near or above its centre of gravity, and free 
to move either in a horizontal plane only, or 
in a vertical plane only, or in both. 

A magnetic needle free to move in a vertical 
plane only is called a dipping needle. A mag- 
netic needle free to move in a horizontal plane 
only, as shown in Fig. 405, is the form employed 

S 




Fig. 40 j Magnetic Xeedle. 

in the mariner's compass. This form of magnetic 
needle is the one most commonly employed. 

For use as a mariner's compass the needle is 
supported on gimbals and placed in a box pro- 
vided with a card on which are marked the 
points of the compass. (See Compass, Azimuth. 
Compass, Points of.) 

Needle, Magnetic, Annual Variations of 

Variations in the value of the mag- 



Nee.] 



378 



[Nee.. 



netic decimation that take piace at regular 
periods of the year. 

The annual variations of the magnetic field were 
discovered by Cassini in 1786. 

Needle, Magnetic, Daily Variation of 

Variations in the value of the magnetic 

declination that take place at different periods 
of the day. 

It was noticed, for example, in London that the 
north pole of the magnetic needle begins to move 
westward between 7 and 8 A. M. and continues 
this movement until I P. M., when -it begins to 
move towards the east until near 10 p. m., when 
it again begins its westward course. 

Needle, Magnetic, Damped —A 

magnetic needle so placed as to quickly come 
to rtst after it has been set in motion. (See 
Damping?) 

Magnetic damping is readily effected by caus- 
ing the needle to move near a metallic plate. On 
the motion of the needle the currents set up in the 
plate by dynamo electric induction tend, accord- 
ing to Lenz's law, to oppose the motions pro- 
ducing them. (See Induction, Electro-Dynamic. 
Laws, Lenz's.) 

Needle, Magnetic, Declination of 



The angular deviation of the magnetic needle 
from the true geographical north. 

The variation of the magnetic needle. 

The declination of the magnetic needle is either 
E. orW. (See Declination, Angle oj .) 

Declination, or variation, is different at dif- 
ferent parts of the earth's surface. 

Lines connecting places which have the same 
value and direction for the declination are called 
isogonal lines. A chart on which the lsogonal 
lines are marked is called a variation chart. 

The value of the declination varies at dif- 
ferent times. These variations of the declination 
are: 

(1.) Secular, or those occurring during great 
intervals of time. Thus, in London, in 1580 the 
magnetic needle had a variation of about 11 
degrees east. This eastern decimation decreased 
in 1622 to 6 degrees E., and in 1680 the needle 
pointed to the true north. In 1692 the declina- 
tion was 6 degrees W. ; in 1730, 13 degrees W. ; 
in 1765, 20 degrees W. ; and 111 1818 the needle 
reached its greatest western declination and is 



now moving eastwards. The declination, how- 
ever, is still west. 

(2.) Annual, the needle varying slightly in it* 
declination during different seasons of the year. 

(3. ) Diurnal, the needle varying slightly in its 
declination during different hours of the day. 

(4.) Irregular, or those which occur during 
the prevalence of a magnetic storm. 

It has been discovered that the occurrence of a 
magnetic storm is simultaneous with the occur- 
rence of an unusual number of sun spots. (See 
Spots, Sun.) 

Needle, Magnetic, Deflection of 

The movement of a needle out of a position of 
rest in the earth's magnetic field or in the 
field of another magnet, by the action of an 
electric current or another magnet. 

The deflection of the needle is sometimes called 
its elongation. This latter term is, however, but 
little used, and is unnecessary. 

Needle, Magnetic, Dipping A 

magnetic needle suspended so as to be tree 
to move in a vertical plane, employed to de- 
termine the angle of dip or the magnetic in- 
clination. (See Dip, Magnetic. Inclination^ 
Magnetic. Incli?io?neter. Chart, Inclina- 
tion) 

A dipping needle is shown in Fig. 406. The 




Fig. 406. Dipping Needle. 

angle B O C, which marks the deviation of the 
needle from the horizontal position, is called the 
angle ot dip. 



Nee.] 



379 



[Neg. 



Needle, Magnetic, Directive Tendency of 

The tendency of a magnetic needle to 



move so as to come to rest in the direction of 
the lines of the earth's magnetic field. 

The directive power of the magnetic needle is 
due to the attraction of the earth's magnetic poles 
for the poles of the needle, or to the action of the 
earth's magnetic field. Since the force of the 
earth's magnetism forms a couple, there is no 
tendency for the needle to move bodily forward 
towards either of the earth's poles. Its tendency 
is merely to rotate until it comes to rest within 
the lines of the earth's magnetic field, entering at 
its south pole, passing through its mass and 
coming out at its north pole. 

Of course this would be true in the case of a 
directing magnet only when it is at a great dis- 
tance from the needle. Otherwise, there would 
be motion towards the poles as well as rotation. 

Needle, Magnetic, Inclination or Dip of 

The deviation of a mechanically bal- 
anced magnetic needle from a horizontal po- 
sition. 

The direction of a magnetic needle in all parts 
of the earth, except at the magnetic equator, 
differs from a level or horizontal position. One 
of its ends inclines or dips towards the ground . 
(See Dip, Magnetic. Needle, Magnetic, Dipping.) 

Needle, Magnetic, Orientation of 

The coming to rest of a magnetic needle in 
the earth's magnetic field. 

Needle, Magnetic, Variation of 

The angular deviation of a magnetic needle 
from the true geographic north. 

The declination of the magnetic needle. 
(See Declination?) 

Needle of Oscillation. — A small magnetic 
needle employed for measuring the intensity 
of a magnetic field by counting the number of 
oscillations the needle makes in a given time, 
when disturbed from its position of rest in 
such field. (See Magnetization, Intensity of. 
Lines, Isodynamic) 

This use of a magnetic needle m determining 
the magnetic intensity of any place is analogous 
to the use of the pendulum in determining the in- 
tensity of gravity at any place. 

Suppose, for example, that at a certain place the 
needle made 245 oscillations in ten minute^, and 



that at another place it made 211 in the same 
time. Then the relative intensities at these two 
places would be as the square of these two num- 
bers, or as 1 : 1.3482. 

Needle, Telegraphic A needle em- 
ployed in telegraphy to represent by its move- 
ments to the left or right respectively the dots 
and dashes of the Morse alphabet. (See 
Telegraphy, Needle System of.) 

Needle, Throw of —A phrase some- 
times used for the angular deflection of a 
needle, particularly when the needle is swing- 
ing. 

The displacement of the magnetic needle is 
called the deflection, the elongation, or the throw. 
The first will appear to be the preferable term 
when the needle comes to rest in a displaced posi- 
tion. 

Negative Charge. — (See Charge, Nega- 
tive?) 

Negative Direction of Electrical Con- 
vection of Heat. — (See Direction, Negative, 
of Electrical Convection of Heat) 

Negative Direction of Simple-Harmonic 
Motion. — (See Motion, Siinple-Harmonic, 
Negative Direction of) 

Negative Electricity. — (See Electricity ; 
Negative.) 

Negative Electrode. — (See Electrode, 
Negative) 

Negative Element of a Yoltaic Cell. — 
(See Element, Negative, of a Voltaic Cell.) 

Negative Feeders. — (See Feeders, Nega- 
tive) 

Negative Omnibus Bars. — (See Bars, 
Negative Omnibus) 

Negative Phase of Electrotonns. — (See 
Electrotonus, Negative Phase of.) 

Negative Plate of Storage Battery. — 
(See Plate, Negative, of Storage Cell.) 

Negative Plate of Voltaic Cell.— (See 
Plate, Negative, of Voltaic Cell) 

Negative Pole. — (See Pole, Negative) 

Negative Potential. — (See Potential, Neg- 
ative) 

Negative Side of Circuit. — (See Circuit, 
Negative Side of.) 



Neg.] 



380 



[Nig. 



Negative Wire. — (See Wire, Negative) 
Negatively. — In a negative manner. 
Negatively Excited. — Charged with nega- 
tive electricity. (See Electricity, Negative) 
Nerve or Muscular Fibre, Excitability 

* of — (See Excitability, Electric, of 

Nerve or Muscular Fibre) 

Nerves, Actio u of Electricity on 



Stimulating and other actions produced in 
nerves by the passage of electricity through 
them, dependent on the direction and char- 
acter of the current. (See Electrotonus. 
Galvanizatio7i. Faradization. Galvano- 
Faradization) 

Net, Faraday's An insulated net 

of cotton gauze, or other similar material, 
capable of being turned inside out without 
being thereby discharged, employed for de- 
monstrating that in a charged, insulated con- 
ductor the entire charge is accumulated on 
the outer surface of the conductor. 




Fig. 407. Faraday's Net. 

Faraday's net, as shown in Fig. 407, consists 
of a bag N, of cotton gauze, or mosquito netting, 
supported on an insulating stand I. When tested 
by a proof plane, no free electric charge is found 
on the inside, though such a charge is readily 
detected by the same means on the outside. By 
the aid of the silk strings S, S, the bag can be 
turned inside out, when the charge will then all 
be found on the then inside, or the now outside. 
Faraday was in the habit of protecting his 
delicate electroscopes against outside electrifica- 
tion by covering them with gauze. To properly 
act as an electric screen, the gauze should be con- 
nected with the earth. 

Faraday constructed a small insulated room, 



twelve feet in height, breadth and depth, covered 
on the inside with tin-foil, and, on charging this 
room from the outside, he was unable to detect 
the presence of any charge on the inside, even by 
the aid of his most delicate instruments. This 
room is often referred to as Faraday's Cube. 

Nets, Torpedo Steel wire netting 

suspended from or attached to a ship's side 
for the purpose of ensuring protection against 
moving torpedoes. 

Network of Currents. — (See Currents, 
Network of. Laws, Kirchhoff 's.) 

Neutral Armature. — (See Armature, 
Neutral.) 

Neutral Feeder. — The feeder that is 
connected with the neutral or intermediate 
terminal of the dynamos in a three-wire sys- 
tem of distribution. (See Feeders.) 

Neutral Line of Commutator Cylinder. 

— (See Line, Neutral, of Commutator 
Cylinder) 

Neutral • Omnibus Bars. — (See Bars, 
Neutral-Omnibus) 

Neutral Point. — (See Point, Neutral) 
Neutral Points of a Dynamo-Electric 
Machine. — (See Points, Neutral, of Dynamo- 
Electric Machine) 

Neutral Points of Mag-net.— (See Points, 
Neutral, of Magnet) 

Neutral Points of Thermo-Electric Dia- 
gram. — (See Points, Neutral, of Thermo- 
Electric Diagram) 

Neutral-Relay Armature.— (See Arma- 
ture, Neutral-Relay) 

Neutral Section of Mag-net.— -(See Sec- 
tion, Neutral, of Magnet) 

Neutral Wire. — (See Wire, Neutral) 
Neutral Wire Ampere-Meter. — (See Am- 
pere-Meter, Balance or Neutral Wire) 
New Ohm. — (See Ohm, New) 
Nickel Bath. -(See Bath, Nickel) 

Nickeling-, Electro Electroplating 

with nickel. (See Plating, Electro) 

Nickel-Plating-.- (See Plating, Nickel) 
Night Bell.- (See Bell, Night) 



tfod.] 



381 



[Noi. 



Nodal Point.— (See Point, Nodal) 

Nodes, Electrical Points in an open 

circuited conductor, through which electrical 
oscillations are passing, which possess a con- 
stant mean value of potential, while the poten- 
tial at its ends alternates between two fixed 
limits. 

Points on a conductor where the strength 
of the induced oscillatory current is equal to 
zero. 

The nodal points on a conductor through which 
electrical oscillations are passing therefore cor- 
respond closely to the nodes on a vibrating wire 
or cord. 

Dr. Hertz employed the following appara- 
tus in order to show the position of two nodes 
in a conductor: An induction coil, A, had its sec- 
ondary terminals connected as shown in Fig. 408, 



-©- 




d, 



-©- 



Fig. 408. Nodes in Conductor. 

\o two metallic spheres, C and C ' . The spark mi- 
crometer circuit, a c d b, was placed near it, as 
shown, and the sparking distance of the secondary 
circuit of the induction eoil adjusted, so that the 
spark micrometer circuit was in unison with it. 
When sparks were passed between the terminals 
of the induction coil A, sparks passed between the 
terminals 1 and 2, at M, under the influence of 
resonant action. 

If, now, a second micrometer circuit, e g h f , 
exactly similar to a c d b, was added, as shown in 
the figure, and the two joined near the terminals 1 
234, by conducting wires, as shown, the entire 
system of the micrometer circuit formed a closed 
metallic circuit, the fundamental vibration of 
which would have two nodes, one at the middle 
point of c d, and the other at g h. The inter- 
nodes would be at the junctions 1 3, and 2 4, and 
under these circumstances a true resonant ac- 
tion existed between the secondary circuit and the 
micrometer circuit, as was shown by the fact that 
any alteration in the circuit e g h f , whether by 



increasing or decreasing its length, diminished 
the sparking distance. Since the conductor con- 
necting points 2, and 4, was in the position of 
the node, where the strength of the excited oscil- 
latory current was zero, its removal from between 
these points should have no influence on the 
intensity of the vibration. This was found on 
trial to be the case. Electrical vibrations may 
therefore be excited by electrical resonance in 
conductors corresponding not only to the simple 
fundamental note or vibration, but also to the 
higher electrical overtones. 

The apparatus shown in Fig. 409, from Tesla, 
illustrates the phenomena of alternative path, as 
well as electric nodes. The terminals of an in- 
duction coil are connected, as shown, to a con- 
denser and to a thick copper conductor. Though 
the two incandescent lamps are placed as shown, 
yet they are raised to luminosity by a species of 
brush discharge that passes through them, al- 
though they would be short circuited to any cur- 
rent but an oscillatory discharge. 




Fig. 40Q. Nodes in a Conductor. 

Nodular Deposit, Electro-Metallurgical 

— (See Deposit, Electro-Metallurgical 

Nodular.) 
Noisy Arc— (See Arc, Noisy.) 



Nom.J 



382 



[Nuhu 



Nominal Candle-Power. — (See Power, 
Candle, Nominal.) 
Non-Automatic YariaMe Resistance.— 

(See. Resistance, Variable, Non-Automatic.) 

Non-Conductors. — Substances that offer 
so great resistance to the passage of an elec- 
tric current through their mass as to practi- 
cally exclude a discharge passing through 
them. 

Non-conductors are cabled insulators, because 
they electrically insulate substances placed on or 
surrounded by them. 

The terms non-conductors or insulators are 
ordinarily used in a relative sense to mean bodies 
which allow no practical or appreciable current 
to pass through them, since there are no sub- 
stances known, apart, perhaps, from the universal 
ether, that absolutely prevent the flow of an elec- 
tric current, the difference of potential of which 
is sufficiently great. 

The entire absence of ordinary matter, as in the 
case of a high vacuum, appears to render a high 
vacuum very nearly, if not entirely, an absolute 
insulator. 

Non-Electrics.— A term formerly applied 
to substances like metals or other conductors 
which appeared not to become electrified by 
friction. 

The term non-electric, was used in contradis- 
tinction to electrics, or substances readily elec- 
trified by friction. The distinction no longer 
holds, since non electrics, if insulated, are readily 
electrified by friction. 

Non-Homogeneous Current-Distribu- 
tion. — (See Current, Non-Homogeneous, 
Distribution of.) 

Non-Illumined Electrode. — (See Elec- 
trode, Non-Illumined?) 

Non-inductive Resistance. — (See Resist- 
ance, Non-inductive.) 

Non-Oscillatory Discharge. — (See Dis- 
charge, Non-Oscillatory?) 

Non-Polarized Armature.— (See Arma- 
ture, Non-Polarized?) 

Non-PolarizaMe Electrodes. — (See Elec- 
trodes, Non-Polar -izable.) 

Non-Wasting Electrode. — (See Electrode, 
Non- Wasting?) 



Normal Day, Magnetic (See Day, 

Normal Magnetic?) 

Northern Light. — The Aurora Borealis. 
(See Aurora Borealis?) 

Notation, Algebraic A system of 

arbitrary symbols employed in algebra. 

The following brief description of the notation, 
employed in algebra is for the use of the non- 
mathematical reader. 

Quantities are represented in algebra by let- 
ters, such as a, and b, x, and y, etc. 

Addition is represented thus: a -f- b. 

Subtraction is represented thus: a — b. 

Multiplication is represented thus: a X b, or 
simply by writing the letters next to each other ab. 

Division is represented thus: a ■+■ b, or — 

An Exponent, or figure placed to the right of a 
letter, above it as a 3 , indicates that the quantity 
represented by a, is to be multiplied by itself three 
times, as a X a X a, or a a a. 

A Co -efficient, or figure placed to the left of a 
quantity, indicates the number of times that quan 
tity is to be taken; thus, 3 a, indicates that a is to- 
be added three times, thus: a-j- a-j-a, or 3 X a. 

K Radical Sion or Root, thus >/a, or 2 >/a, 
indicates that the square root of the quantity a x 
is to be taken. In the same manner 3 \i a, indi- 
cates that the cube root of a is to be taken. 

These expressions are sometimes written aJ, or" 



Equality is indicated thus: a 3 =a XaXa, or 

1 __ 

a * = v/a. 

A negative exponent a -2 indicates \, or is the 

a 3 
exponent of the reciprocal of the quantity indi-- 
cated. 

Null or Zero Method.— (See Method, 
Null or Zero?) 

Null Point.— (See Point, Null?) 



Number, Diacritical 



-Such a num- 



ber of ampere-turns at which a given core 
would receive a magnetization equal to half 
saturation. 



Obs.] 



383 



[Ohm. 



£1. — A contraction for megohm. (See 
Ohm, Meg) 

go. — A contraction for ohm. (See O/im.) 

Obscure Heat. — (See Heat, Obscure) 

Observation Mine. — (See Mine, Observa- 
tion) 

Observatory, Magnetic An obser- 
vatory in which observations of the variations 
in the direction and intensity of the earth's 
magnetic field are made. 

Magnetic observatories are generally furnished 
with self-registering magnetic apparatus, such as 
magnetographs, magnetometers, inclinometers. 
(See Magnetometer. Magnetograph. Inclinome- 
ter.) 

Magnetic observatories are generally con- 
structed entirely of non-magnetic materials; that 
is, of such materials as ai?e destitute of paramag- 
netic properties. 

Obtuse Angle. — (See Angle, Obtuse) 

Occlusion of Gas. — (See Gas, Occlusion 
of) 

Odorscope. — An apparatus in which the 
determination of an odor was attempted by 
the measurement of the effect the odorous 
vapor, or effluvia, produced on a variable 
contact resistance. 

The microtasimeter was used in connection 
with the odorscope. (See Diagomeler, Rons- 
seau's. Microtasimeter.) 



Oerstedt, An 



•A proposed term for 



the unit of electric current, in place of an 
ampere. 

The term has not been adopted. 

Ohm. — The unit of electric resistance. 

Such a resistance as would limit the flow 
of electricity under an electromotive force of 
one volt to a current of one ampere, or to one 
coulomb per second. (See Unit, B.A. Ohm, 
Legal. Ohm, Standard) 

A value equal to io 9 absolute electro-mag- 
netic units. 

A value which is represented by a velocity 
of io , or i,ooo,ooo,ooo centimetres per second. 



It may be difficult at first to see how resistance 
can be correctly represented by a velocity. The 
following consideration may render this clear : 
The formula for calculating the velocity is 

D 

V = y-p or the velocity equals the distance passed 

through in unit time. Now, by examining the 
formula for the value of the resistance, expressed 
in terms of the electro-magnetic units (see 
Units, Electro-Magnetic, Dimensions of), it may 
be seen to be that resistance = 

Electromotive force L 

Cunent. T* 

But this value is of the nature of a velocity, 
being equal to the length, divided by the time. 
Resistance, therefore, has the dimensions of a 
velocity. 

This is clearly expressed by Silvanus P. Thomp- 
son in his "Elementary Lessons in Electricity 
and Magnetism," as follows, viz.: " Suppose we 
have a circuit composed of two horizontal coils, 
C S, and D T (Fig. 410), I centimetre apart, 
joined at C D, and completed by means of a 
sliding piece, A B. Let this variable circuit be 
placed in a uniform magnetic field of unit inten- 
sity, the lines of force being directed vertically 
downwards through the circuit. 

"If, now, the slider be moved along towards 
S T, with a velocity of n, centimetres per second, 
the number of additional lines of force embraced 
by the circuit will increase at the rate of n, per 
second ; or, in other words, there will be an in- 




V ~*A. T 

Fig. 410. Resistance as a Velocity. 

duced electromotive force i npressed upon the cir- 
cuit, which will cause a current to flow through 
the slider from A to B. Let the rails have no 
resistance, then the strength of the current will 
depend on the resistance of A B. Now, let A B, 
move at such a rate that the current shall be of 
unit strength. If its resistance be one absolute 
(electro-magnetic) unit, it need only move at the 
rate of 1 centimetre per second. If its resistance 
be greater, it must move with a proportionately 



Ohm.] 



384 



[Ohm. 



greater velocity ; the velocity at which it must 
move to keep up a current of unit strength being 
numerically equal to its resistance. The resist- 
ance known as " I ohm ' ' is intended to be io 9 ab- 
solute electro -magnetic units, and, therefore, is 
represented by a velocity of io 9 centimetres, or 
10,000,000 metres (/ earth-quadrant) per 
second. ' ' 

Ohm, B. A. A contraction for 

British Association ohm. 

Ohm, Board of Trade A unit of re- 
sistance as determined by a committee of the 
English Board of Trade. 

A committee consisting of Sir W. Thomson, 
Lord Rayleigh, Dr. J. Hopkinson and other 
authorities appointed by the Board of Trade 
(England) has recently recommended that the 
ohm be taken as the resistance of a column of 
mercury 106.3 centimetres in length and one 
square millimetre area of cross-section at o de 
grees C. and since this value agrees with the best 
experimental results, it will probably be generally 
and finally adopted. 

Ohm, British Association The 

British Association unit of resistance, 
adopted prior to 1884. 

The value of the unit of electric resistance, or 
the ohm, was determined by a Committee of the 
British Association as being equal to the resistance 
at o degree C. of a column of mercury I square 
millimetre in area of cross-section and 104.9 
centimetres in length. This length was taken as 
coming nearest the value of the true ohm de- 
uuced experimentally from certain theoretical 
considerations. Subsequent re-determinations 
showed the value so obtained to be erroneous. 

The value of the ohm is now taken internation- 
ally, as adopted by the International Electric 
Congress in 1884, as the resistance of a column 
of mercury 106 centimetres in length, and I 
square millimetre in area of cross-section. This 
last value is called the legal ohm, to distinguish it 
from the B. A. ohm, which, as above stated, is 
equal to a mercury column 104.9 centimetres in 
length. Usage now sanctions the use of the 
word ohm to mean the legal ohm. 

This value of the legal ohm is provisional until 
the exact length of the mercury column can be 
finally determined. (See Ohm, Board of Trade.) 

The following are the relative values of these 
units, viz. : 



1 legal ohm = 1 .01 12 B. A. ohm. 

" " =1 .0600 Siemens unit. 

1 B. A. ohm = .9889 legal ohm. 

1 " " = 1.0483 Siemens unit. 

1 Siemens unit = .954° B. A. ohm. 

" " = «9434 legal ohm. 

Ohm, Legal The resistance of a 

column of mercury 1 square millimetre in 
area of cross-section, and 106 centimetres in 
length, at the temperature of o degree C. or 
32 degrees F. (See Unit, B. A.) 

1 ohm = 1.00112 B. A. units. This value of 
the ohm was adopted by the International Elec- 
tric Congress, in 1884, as a value that should be 
accepted internationally as the true value of the 
ohm. This value, however, was provisional, and 
was never actually legalized. It will probably be 
replaced by the new (106.3 cm -) onm - (See 
Ohm, Board of Trade.) 

Ohm, Meg" One million ohms. 

Ohm, New A term sometimes used 

for the Board of Trade ohm. (See Ohm, 
Board of Trade) 

Ohm, Standard A length of wire 

having a resistance of the value of the true 
or legal ohm, employed in standardizing re- 
sistance coils. 

The standard ohm, as issued by the Electric 
Standards Committee of England, Las the form 




Fig. 41 1. Standard Ohm. 

shown in Fig. 411. The coil of wire is formed 
of an alloy of platinum and silver, insulated by 
silk covering and melted paraffine. Its ends are 
soldered to thick copper rods r, r', for ready 
connection with mercury cups. The coil is at 
B. The space above it at A, is filled with paraffine, 
except at the opening t, which is provided for 
the insertion of a thermometer. 



Oiim.J 



385 



[Ope, 



Ohm, True An ohm having the 

true theoretical value of the ohm. (See Ohm.) 

Ohmage.— The value of the resistance of 
a circuit expressed in ohms. 

Ohmic Resistance. — (See Resistance, 
O/imi'c or True.) 

Ohmmeter. — A commercial galvanometer, 
devised by Ayrton, for directly measuring by 
the deflection of a magnetic needle, the re- 
sistance of any part of a circuit through 
which a strong current of electricity is 
flowing. 

Ayrton's ohmmeter is represented diagram- 
matically in Fig. 412. Two coils C C, and c c, 




Fig. 412. Ayrton's Ohmmeter. 

consisting of a short thick wire, and a long thin 
wire, respectively, are placed at right angles to 
each other, and act on a soft iron needle situated 
as shown. The short, thick wire coil C C, is con- 
nected in series with the resistance O, to be 
measured. The long, fine wire coil, of known 
high resistance, is placed as a shunt to the un- 
known resistance. 

Under these circumstances, it can be shown 
that the action on the needle is that due to the ratio 
of the difference of potential at the terminals of 
the unknown resistance and the current strength 

in the thick wire coil, or R = — , as may be 

\-> 
deduced from Ohm's law. 

The coils are so proportioned that the current 
when flowing through the short thick wire moves 
the needle to the zero of the scale, while the long 
thin wire produces a deflection directly propor- 
tional to the resistance. 

Ohm's Law. — (See Law of Ohm) 

Oil, Colza An oil obtained from the 

seed of the Brassica oleracea, a species of 
cabbage. 

Colza oil is extensively used for purposes of il- 
lumination and in the carcel standard lamp. (See 
Lamp, Carcel.) 



Oil Cup. — A cup containing oil for lubri 
eating machinery. 

Oil Insulator. — (See Insulator, Oil.) 

Oil Transformer. — (See Transfor?ner, 
Oil.) 

Oiler, Automatic An oil cup or res- 
ervoir that automatically spreads oil over the 
bearings of machinery in motion. 

Okonite. — A variety of insulating material. 

Omnibus Bars. — (See Bars, Omnibus) 

Omnibus Wires. — (See Wires, Omnibus.) 

Opacity, Selective Opaque in a cer- 
tain direction or directions only. 

Certain substances are opaque to polarized light 
in certain planes only. Thus, a plate of tourma- 
line permits light polarized in a certain p'ane 
freely to pass through it, but is entirely opaque 
in a plane at right angles thereto. 

S. P. Thompson and Lodge have shown that 
such crystals of tourmaline possess curious prop- 
erties in regard to the conduction of heat. While 
warming, the crystal conducts heat better in a cer- 
tain direction than in the opposite direction. While 
cooling, exactly the opposite effects are observed. 
In the same manner, while the crystal is rising i:i 
temperature, there is an accumulation of positive 
electricity at one end, and negative at the other. 
While the crystal is cooling, the reverse is true. 

Open-Box Conduit.— (See Conduit, Open- 
Box) 

Open Circuit. — (See Circuit, Open) 

Open-Circuit Electric Oscillations. — 

(See Oscillations, Ope?i-Circuit, Electric) 
Open-Circuit Induction. — (See Induction, 

Open-Circuit) 
Open-Circuit Oscillation, Period of 

— The time in which the oscillations set up in 
a circuit by electrical resonance require to 
make a complete one to-and-fro motion. 

The period of an open - circuit electric oscillation 
is determined by the product of the co-efficients 
of self-induction of the conductor, and does not 
depend on the composition of the terminals. It is 
practically independent of their resistances. 

Open-Circuit Single-Current Signaling. — 

(See Signaling, Single-Current, Open- 
Circuit) 



Ope.] 



386 



[Ore. 



Open-Circuit Toltaic Cell. — (See Cell, 
Voltaic, Open-Circuit^ 

Open-Circuit Voltmeter. — (See Volt- 
meter, Open-Circuit, ,) 

Open-Circuited. — Put on an open circuit. 

Open-Circuited Conductor. — (See Con- 
ductor, Open-Cir cuited) 

Open-Circuited Thermostat. — (See Ther- 
mostat, Open-Circuit.) 

Open-Coil Drum Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric, 
Open-Coil Drum?) 

Open-Coil Dynamo-Electric Machine. — 

(See Machine, Dynamo-Electric, Open-Coil.) 

Open-Coil Ring Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric, 
Open-Coil Ring) 

Open-Iron-Circuit Transformer. — (See 
Transformer, Open-Iron-Circuit) 

Open-Iron Magnetic Circuit. — (See Cir- 
cuit, Open-Iron Mag?ietic.) 

Open Magnetic Core. — (See Core, Ope?i- 
Magnetic.) 

Opening Shock. — (See Shock, Opening.) 

Operation, Magnet The use of a 

magnet for the purpose of removing particles 
of iron from the human eye. 

Optical Strain. — (See Strain, Optical) 

Optical Strain, Electro-Magnetic 

(See Strain, Optical Electro-Magnetic) 

Optical Strain, Electrostatic (See 

Strain, Electrostatic, Optical) 

Optics, Electro That branch of 

electricity which treats of the general relations 
that exist between light and electricity. 

The phenomena of electro-optics may be ar- 
ranged under the following heads, viz.: 

(i.) Electrostatic stress, produced by an 
electrostatic field causing an optical strain in a 
transparent medium, whereby such medium 
acquires the property of either rotating the plane 
of polarization of a beam of plane polarized light, 
or of doubly refracting light. 

(2.) Electro magnetic stress produced by a 



magnetic field causing an optical strain in a trans- 
parent medium, whereby such medium acquires 
the property of either rotating the plane of polar- 
ization, or of doubly refracting light. (See Re- 
fraction, Double, Electric.) 

(3.) Changes in the electric resistance of bodies 
caused by the action of light. (S^e Cell, Sele- 
nium. ) 

(4. ) The relation existing between the values of 
the index of refraction of a transparent medium 
and its specific inductive capacity. (See Refrac- 
tion. Capacity, Specific Inductive.) 

This relation has been shown to be as follows : 

The specific inductive capacity is approxi- 
mately equal to the square of the index of re- 
fraction. 

(5.) The relation existing between the velocity 
of light and the value of the ratio of electrostatic 
and the electro-magnetic units, thus giving a 
basis for an electro-magnetic theory of light. 
(See light, Maxwell's Electro-Magnetic Theory 
of) 

Polarized light reflected from the surface of a 
magnet, although it penetrates the substance to 
but a trifling extent, yet has its plane of polariza- 
tion distinctly rotated by the magnetic whirls in 
the iron. 

Oral or Speaking-Tuhe Annunciator.— 

(See Annunciator, Oral or Speaking- Tube) 
Ordinate. — A distance taken on a per- 
pendicular line called the axis of ordinates, in 
contradistinction to the axis of abscissas. 
(See Ordinates, Axis of) 

Thus in Fig. 413, D 1, is the ordinate of the 
point D, in the curve O D R. 



Ordinates, Axis of - 

of co-ordinates used 



One of the axes 





for determining the 
position of the points 
in a curved line. 

Thus in Fig. 413 the 
line A B, is called the axis 
of ordinates because it is 
the line on which the or- 
dinate 2 D, is measured. Z 

Ores, Electric 
Treatment of Processes for the ex- 
traction of metals from their ores. 

These processes are referable to three dis- 
tinct classes, viz. : 




4 13. Axis of Ordi- 
nates. 



Org.; 



387 



[Osm« 



. (I.) Those in which the reduction is effected by 
means of heat of electric origin. 

(2.) Those in which the reduction is effected by 
the combined action of heat and electrolysis. 

(3.) Those in which the reduction is effected by 
means of electrolysis only. 



Organ, Electric 



-A wind organ, in 



-which the escape of air into the different 
pipes is electrically controlled. 

In an electric organ, the keys, instead of oper- 
ating levers, as usual, to admit the passage of air 
into the pipes, merely complete the circuit of a 
battery through a series of controlling electro-mag- 
nets. With such an arrangement, the keyboard 
can be placed at any desired distance. 

Electric organs have been constructed, in which 
a chemical or mechanical record is made of the 
notes struck by the performer, as well as the 
musical value of such notes. By such a device 
the musical creations of a composer are perma- 
nently recorded in characters that are capable of 
interpretation by a compositor skilled in musical 
notation. 

Orientation of Magnetic Needle. — (See 
Needle, Magnetic, Orientation of.) 

Origin, Point of The point where 

the axes of co-ordinates start or originate. 
(See Co-ordinates, Axes of.) 

Orthogonal. — Rectangular, or right-an- 
gled. 

Oscillating Discharge. — (See DisoJiarge, 
Oscillating?) 

Oscillating Needle.— (See Needle of Oscil- 
lation?) 



Oscillation, Centre of 



-A point in 



a body swinging like a pendulum, which is 
neither accelerated nor retarded, during its 
oscillations, by the portions of the pendulum 
that are situated respectively above or below it. 

If all the mass were concentrated at the centre 
of oscillation the time of oscillation would be the 
same. 

The centre of oscillation is always below the 
centre of gravity. The vertical distance between 
the centre of oscillation and the point of support 
of a pendulum, determines the virtual length of 
the pendulum, and hence its number of vibra- 
tions per second. (See Pendulum, Laws of.) 



Oscillations, Electric The series 

of partial, intermittent discharges of which 
the apparent instantaneous discharge of a 
Leyden jar through a small resistance actu- 
ally consists. 

These partial discharges produce a series of 
electric oscillations of the current in the circuit of 
the discharge, which consist of true to and-fro 
or backward -and-forward motions of the elec- 
tricity. This phenomenon was discovered by 
Joseph Henry. 

Oscillations, Open-Circuit, Electric 

— Electric oscillations produced in open cir- 
cuits by the presence of electric pulses in 
neighboring circuits. 

Oscillatory Discharge. — (See Discharge, 
Oscillatory?) 

Oscillatory Electric Displacement. — (See 
Displacement, Electric, Oscillatory?) 

Oscillatory Electromotive Force. — An 

electromotive force which is rapidly periodic. 

Oscillatory Inductance. — (See Induc- 
tance, Oscillatory, Electric?) 

Oscillatory Induction. — (See Induction, 
Oscillatory?) 

Osmose. — The unequal mixing of liquids of 
different densities through the pores of a 
separating medium. 

If a solution of sugar and water be placed in a 
bladder, the neck of which is tied to a straight 
glass tube, and the bladder is then immersed in a 
vessel of pure water with the tube in a vertical 
position, the two liquids will begin to mix, the 
sugar and the water passing through the bladder 
into the pure water, and the pure water passing 
into the sugar and water in the bladder. This 
latter current is the stronger of the two, as will be 
shown by the water rising in the vertical glass 
tube. 

The stronger of the two currents, that is, the 
one directed towards the higher level, or the one 
which produces the higher level, is called the en- 
dos?notic current, and the weaker current the 
exosmotic current. 

Osmose, Electric A difference of 

liquid level between two liquids placed on 
opposite sides of a diaphragm produced by 
the passage of a strong electric current 



Osni.J 



388 



[Ozo. 



through the liquids between two electrodes 
placed therein. 

The higher level is on the side towards which the 
current flows through the diaphragm, thus appa- 
rently indicating an onward motion of the liquid 
with the current, or, in other words, the liquid is 
higher around the kathode than around the anode. 
The difference of level is most marked when 
poorly conducting liquids are employed. 

As a converse of this, Quincke has shown that 
electric currents are set up when a liquid is forced 
by pressure through a porous diaphragm. The 
term diaphragm currents has been proposed for 
these currents. Their electromotive force depends 
on the nature of the liquid, on the material of the 
diaphragm, and on the pressure that forces the 
liquid through the diaphragm. (See Phenomena, 
Electro-Capillary . Currents, Diaphragm.) 

Osmotic — Of or pertaining to osmose. 
(See Osmose) 

Osteotome, Electric A revolving 

electrically propelled saw, employed in the 
surgical cutting of bones. 

An electric osteotome consists essentially of a 
form of revolving engine known as a dental en- 
gine, furnished with a circular saw, or other ro- 
tary cutter, driven or propelled by electricity. 

Outgoing Current— (See Current, Out- 
going) 

Outlet. — In a system of incandescent lamp 
distribution the places in a building where 
the fixtures or lamps are attached. 

The outlets are left in a building by the wire- 
man for the electric fixtureman to attach the de- 
vice intended to be used on the circuits so pro- 
vided. 



Output, Magnetic 



-The product of 



the magnetic flux by the magneto-motive 
force. 

Output of Dynamo-Electric Machine. — 

(See Machine, Dynamo-Electric, Output of) 

Outrigger for Electric Lamp. -A device 
for suspending an electric arc lamp so as to 
cause it to stand out from the wall of a 
building. 

An outrigger and hood with lamp attached are 
shown in Fig. 414. 



Outrigger Torpedo. -(See Torpedo, Out- 
rigger) 

Over-Compounded.— The compounding of 
a dynamo-electric machine so as to produce 




Outrigger and Hood. 



an increase of voltage under increase of load. 
Over-compounding is generally employed for 
compensating for drop or loss of potential in the 
line or conductor, and is adjusted to a definite 
percentage of increase from light to full load in 
accordance with the amount of drop, or loss, for 
which such compensation was designed. 

Overhead Lines. — (See Lines, Overhead) 

Overhead System, Continuous, of Motive 

Power for Electric Railroads (See 

Railroads, Electric, Continuous Overhead 
System of Motive Power for) 

Overload of Electric Motor.— (See Motor r 
Electric, Overload of ) 

Overtones.— Additional, faint tones, ac- 
companying nearly every distinct musical 
tone, by the presence of which the peculiarity 
or quality of such tone is produced. (See 
Sound, Characteristics of) 

Overtones, Electric Electric vibra- 
tions produced in open-circuited conductors 
by electric resonance, of higher rates than the 
fundamental vibrations. 

The existence of electrical overtones necessitates 
the existence of electric nodes. (See Nodes, Elec- 
trical.) 

Overtype Dynamo.— (See Dynamo, Over- 
type) 

Ozite. — An insulating substance. 

Ozokerite. — An insulating substance. 



Ozo.J 



389 



LPar. 



Ozone. — A peculiar modification of oxygen 
which possesses more powerful oxidizing 
properties than ordinary oxygen. 

Ozone is now generally believed to be tri- 
atomic oxygen, or oxygen in which the bonds are 
closed, thus: 

Q 



O- 



The peculiar smell observed when a torrent of 
electric sparks passes between the terminals of 
a Holtz machine, or a Ruhmkorff coil, is caused 
by the ozone thus formed. 

In a similar manner ozone is formed in the at- 



mosphere during the passage through the air of a 
flash of lightning. 

During the so-called electrolysis of water, a com- 
pound formed by the union of two volumes of 
hydrogen with one volume of oxygen, some of the 
oxygen is given off in the form of ozone. Since 
ozone has a somewhat smaller volume than that 
of the oxygen forming it, the volume of the 
oxygen liberated is somewhat less than half the 
volume of the hydrogen. 

There are a number of different forms of ap- 
paratus designed for the production of ozone. 
They consist essentially either of means for pass- 
ing a torrent of electric sparks through air or for 
producing a species of polarization in the air. 



P. D. or p. d. — A contraction frequently em- 
ployed for difference of potential. (See Poten- 
tial, Difference of.) 

Pacinotti Projections. — (See Projections, 
Pacinotti.) 

Pacinotti Ring. — (See Ring, Pacinotti.) 

Pair, Astatic A term sometimes 

applied to an astatic couple. (See Couple, 
Astatic.) 

Palladium. — A metal of the platinum 
group. 

Metallic palladium has a tin-white color, and, 
when polished, a high metallic lustre. It is 
tenacious and ductile, and, like iron, can be 
welded at a white heat It is very refractory and 
possesses in a marked degree the power of ab- 
sorbing or occluding hydrogen and other gases. 
It is not affected by oxygen at any temperature, 
nor readily affected by ordinary corrosive agents. 

Palladium Alloy.— (See Alloy, Pal- 
ladium^ 



Pane, Magic 



-A condenser formed 



of a sheet of glass covered on one side with 
pieces of tin-foil with small spaces between 
them pasted in some design on the glass. 

On the discharge of a Leyden jar through these 
metallic pieces, the design is seen as a series of 
minute sparks, which bridge the spaces between 
the adjacent pieces of foil. 



Pantelegraphy. — A system for the tele- 
graphic transmission of charts, diagrams, 
sketches or written characters. 

Pantelegraphy is more frequently called fac- 
simile telegraphy. (See Telegraphy, Fac- Simile.) 

Paper Carbons. — (See Carbons, Paper?) 

Paper Cut-Out.— (See Cut-Out, Paper?) 

Paper Perforator. — (See Perforator, 
Paper?) 

Paper Winder, Automatic A de- 
vice, driven by clockwork, for automatically 
delivering the paper fillet on which a tele- 
graphic message is received. 

Parabolic Reflector.— (See Reflector, 
Parabolic?) 

Paraffine. — A name given to various 
solid hydrocarbons of the marsh gas series, 
that are derived from coal oil or petroleum by 
the action of nitric acid. 

Paraffine possesses excellent powers of insula- 
tion, and forms a good dielectric medium. Dried 
wood, boiled in melted paraffine, forms a fair in- 
sulating material. 

Paraffine Wire. — (See Wire, Paraffine?) 

Paraffining. — Covering or coating with, 
paraffine. 

The paraffine is applied, while melted by heat, 
either by means of a brush, or by dipping the 
article in the fused mass. 



Par.] 



390 



[Par. 



Care must be taken in paraffining wooden or 
other absorbent articles, to dry them before im- 
mersing in the melted paraffine, since, if water be 
pre>ent, steam is formed explosively, and the 
melted paraffine scattered in all directions. 

Paragreles. — Lightning rods, intended to 
protect fields against the destructive action of 
hail. (See Hail, Assumed Electrical Ori- 
gin of.) 

It was formerly believed that hail is caused by 
electricity. It is now generally believed that the 
electricity in hail storms is caused by the hail. 
It will, therefore, readily be understood that para- 
greles can afford no real protection. 

Parallax. — The apparent angular displace- 
ment of an object when seen from two dif- 
ferent points of view. 

In reading the exact division on a scale to which 
a needle points, care must be taken to look di- 
rectly down on the needle, and not sideways, so 
as to avoid the error of displacement due to 
parallax. 

Parallel Circuit. — (See Circuit, Parallel.) 

Parallel Series. — (See Series, Parallel) 

Parallelogram of Forces. — (See Forces, 
Parallelogram of.) 

Parallels, Magnetic Lines connect- 
ing places on the earth's surface at right 
angles to the isogonal lines, or lines of equal 
declination or variation. 

The magnetic parallels are at right angles to 
the magnetic meridians. The magnetic parallels 
"lie in planes parallel to the magnetic equator. 
(See Needle, Magnetic, Declination of . Meridian, 
Magnetic. ) 

Paramagnetic. — Possessing properties or- 
dinarily recognized as magnetic. 

Possessing the power of concentrating the 
lines of magnetic force. 

Paramagnetic is a term employed in contra- 
distinction to diamagnetic. (See Diamagnetic.) 
A paramagnetic substance, cut in the form of a 
bar whose length is much greater than its breadth 
and thickness, will, when suspended in a magnetic 
field in the manner shown in Fig. 415, take up a 
position of rest with its greatest length in the direc- 
tion of the lines of force, i. e., will point axial ly. 




Fig 415. D.amagn-tic 
Polarity 



In other words, the lines, of force will so pass 
through the paramagnetic substance as to reduce 
the magnetic resistance of the circuit as much as 
possible. 

Paramagnetic substances, therefore, concen- 
trate the lines of force on them. (See Resistance, 
Magnetic.) 

Diamagnetic substances, on the contrary, when 
placed as shown in Fig. 415, assume a position of 
rest with their least dimensions in the direction of 
the lines of force, i. e. 
they point equatorially. 
This is the position in 
which they are placed 
by the lines of force, in 
order to insure the least 
magnetic resistance in 
the circuit of these lines. 
The magnetic resistance 
of diamagnetic sub- 
stances is great as com- 
pared with that of par- 
amagnetic substances. 

The term ferro -mag- 
netic has been proposed 
for paramagnetic. If 
another term be required, which is doubtful, 
sidero-magnetic, proposed by S. P. Thompson, 
would appear to be preferable. (See Magnetic, 
Ferro. Magnetic, Sidero.) 

Tyndall believes that the magnetic polarity 
possessed by diamagnetic substances is the result 
of a distinct polar force, different in its nature 
from ordinary magnetism. His views, in this re- 
spect, are not generally accepted. (See Polarity, 
Diamagnetic. ) 

Paramagnetically. — In a paramagnetic 
manner. (See Paramagnetism.) 

Paramagnetism. — The magnetism of a 
paramagnetic substance. 

Parasitical Currents. — (See Currents, 
Parasitical.) 

Paratonnere. — A French term for light- 
ning rod, sometimes employed in English 
technical works. 

Lightning rod would appear to be the prefer- 
able term. 

Partial Contact. — (See Contact, Partial) 
Partial Disconnection. — (See Disconnec- 
tion, Partial) 



Par.] 



391 



[Pen. 



Partial Earth.— (See Earth, Partial) 

Partial Reaction of Degeneration. — (See 
Degeneratio?i, Partial Reaction of) 

Passive State. — (See State, Passive) 

Path, Alternative The path or 

circuit taken by an impulsive discharge, in 
preference to another path or circuit, open to 
the discharge, although of enormously smaller 
ohmic resistance. 

The alternative path is the path taken by the 
discharge produced by what was formerly called 
lateral induction. 

The explanation of the reason the discharge 
takes the alternative path is that the counter-elec- 
tromotive force of self-induction of the circuit, 
produced by the impulsive discharge, is so great 
as to make the path of the circuit itself, although 
formed of conducting materials, practically non- 
conducting. 

If a Leyden jar is provided with discharge wires 
or conductors, as shown is Fig. 416, a discharge 



would pass across an air space in preference to 
a metallic circuit, was greater for a thick copper 




fc!. 



Fig. 416. Phenomena of Alternative Path. 

taking place at A, is accompanied simultaneously 
by an even longer spark at B, between the ends 
of two long open-circuit leads. 

To explain in a general manner the phenomena 
of the alternative path, we may say that the dis- 
charge at A, gives rise to electric oscillations in the 
leads connected with B, and that there are sent out 
into the surrounding medium radiations of pre- 
cisely the same nature as those which produce 
light, only of a wave length so long as to be un- 
able to produce on the eye the effects of light. 

If the space between the balls at B, is too great 
for the discharge to take place, the wires glow 
and throw out minute sparks or brushes of light. 

The action of the ordinary lightning arrester 
depends on the principle of the alternative path. 
The resistance of the metallic circuit, composed 
of the line and the instruments, is so great in the 
case of the impulsive discharge of a lightning 
flash, that the discharge takes place between a 
series of points connected with the line plate and 
another series of points connected with the ground 
plate. (See Arrester, Lightning ) 

Dr. Lodge, who has studied the principle of 
alternative path in the case of lightning rods, 
finds that the distance at which the discharge 




SPRHMXHs 



Fig. 417. Edison Electric Pen. 

rod, 40 feet long, than for an iron rod of No. 27 
B. W. G. of 33.03 ohmic resistance. 

Patrol Alarm Box. 

—(See Box, Patrol 
Alarm) 

Peltier Effect. — 

(See Effect, Peltier) 

Pen Carriage. — 

(See Carriage, Pen) 

Pen, Electric 

— A device for mani- 
fold copying, in which 
a sheet of paper is 
made into a stencil by 
minute perforations 
obtained by a needle 
driven by a small 
electric motor and the 
stencil afterwards em- 
ployed in connection 
with an inked roller 
for the production of 
any required number 
of copies. 

Mechanical pens are 
constructed on the same 
principle, the perfora- 
tions being obtained by 
mecnanical instead of 
by electric power. 

In the Edison electric 
pen, Fig. 417, the per- -^ 4l8- Electric Pendant. 
forations are made by an electric motor driven 
by a voltaic battery. The manifold press with 
its inked pad is shown to the left of the figure. 

Pendant Cord.— (See Cord, Pendant) 

Pendant, Electric A hanging fix- 




Pen.] 



392 



[Per. 



ture provided with a socket for the support of 
an incandescent lamp. 

A form of electric pendant is shown in Fig. 
418. 

Pendant, Flexible Electric Light 

— A pendant for an incandescent lamp formed 
by the flexible conductors which support the 
lamp. 

The advantages procured by a flexible pendant 
are evident in that both the length of the flexible 
conductor from which the lamp is hanging and 
position of the lamp can be changed considerably. 

Pendulum Annunciator. — (See Annun- 
ciator, Pendulum or Swinging.) 

Pendulum, Electric A pendulum 

so arranged that its to-and-fro motions send 
electric impulses over a line, either by making 
or breaking contacts. 

An electrical tuning fork whose to-and-fro 
movements are maintained by electric im- 
pulses. 

Electric pendulums are employed in systems 
for the electrical distribution of time. 

Sometimes instead of using true pendulums for 
such purposes, coils, mounted on tuning forks, or 
on the ends of flexible bars of steel, called reeds, 
are used for the purpose of establishing cur- 
rents, or modifying the currents that are already 
passing in a circuit. The movement of a mag- 
netic diaphragm, as in the case of a telephone 
diaphragm, towards and from a coil of wire, is 
another illustration of an electric pendulum. 

Electric tuning-fork pendulums are employed 
in Delany's system of synchronous- multiplex teleg- 
raphy, and in Gray's harmonic-multiple teleg- 
raphy. (See Telegraphy, Synchronous -Multi- 
plex, Delany's Sy 'stem. Telegraphy, Gray's Har- 
monic-Multiple. ) 

Pendulum, Laws of — The laws 

which express the peculiarities of the motion 
of a simple pendulum. 

A simple pendulum is one in which the entire 
weight is considered as concentrated at a single 
point, suspended at the end of a weightless, in- 
flexible and inextensible line. 

The following are the laws of the simple pen- 
dulum : 

(1.) Oscillations of small amplitude are approx- 
imately isochronous; that is, are made in times 
that are sensibly equal. (See Vibration or Wave, 
Amplitude of. Jsochronism.) 



(2.) In pendulums of different lengths, the 
duration of the oscillations is proportional to the 
square root of the length of the pendulum. 

(3.) In the same pendulum, the length being 
preserved invariable, the duration of the oscilla- 
tion is inversely proportional to the square root 
of the intensity of gravity. 

The intensity of gravity, at any latitude, may 
be determined by the number of oscillations of a 
pendulum of a given length. In the same man- 
ner the intensity of a magnetic field, or the in- 
tensity of magnetization of a magnet, may be de- 
termined by the needle of oscillation, by observing 
the number of oscillations a needle makes in a 
given time when disturbed from its position of 
re,t. (See Needle of Oscillation.) 

Since a simple physical pendulum is a physical 
impossibility, the virtual length of a pendulum, 
that is, the vertical distance between its point of 
support and the centre of oscillation, is taken as 
the true length of the pendulum. 

If the irregularly shaped body, shown in Fig. 
419, whose centre of gravity is at G, is made to 
swing like a pendulum, either on 
S, or O, its oscillations will be 
performed in equal times, and 
the body will act as a simple 
pendulum, whose virtual length 
is SO. 

If, while suspended at S, it be 
struck at O, it will oscillate 
around S, without producing^ 4ig Centre 
any pressure on the supporting of Oscillation. 
axis at S, on which it turns. If floating entirely 
submerged in a liquid, a blow at O, would cause 
it to move in a straight line in the direction of 
the blow, without rotation. 

The point O, is called the centre of percussion, 
or the centre of oscillation. The centre of oscil- 
lation is always below the centre of gravity. 

Pentane Standard. — (See Standard, Pen- 
tane.) 

Percussion, Centre of That point in 

a body suspended so as to move as a pendu- 
lum at which a blow would produce rotation, 
but no forward motion, or motion of transla- 
tion. 

Perforator, Paper An apparatus 

employed in systems of automatic telegraphy 
for punching in a fillet of paper the circular or 
elongated spaces that produce the dots and 




Per.] 



393 



[Per. 



dashes of the Morse alphabet, when the fillet is 
drawn between metal terminals that form the 
electrodes of a battery. (See Telegraphy, 
Automatic?) 

Perforator, Pneumatic A paper 

perforator operated by means of compressed 
air. (See Perforator, Paper?) 

Period of Open-Circuit Oscillation. — (See 
Open-Circuit Oscillation, Period of.) 

Period of Simple-Harmonic Motion. — 
(See Motioft, Simple-Har7nonic, Period of.) 

Period of Titration. — (See Vibration, 
Period of.) 

Period, Vibration The period of a 

single or a whole vibration in a conductor, in 
which an oscillatory vibration is being pro- 
duced by electrical resonance when respond- 
ing to its fundamental vibration. 

Hertz gives the following value for the vibration 
period: Calling T, the single or half vibration 
period ; L, the co-efficient of self-induction in abso- 
lute magnetic measure, and therefore expressed in 
centimetres; C, the capacity of the terminal-;, in 
electrostatic measure, and therefore also expressed 
in centimetres; v, the velocity of light in centi- 
metre seconds, then, when the resistance of the con- 
ductor is small, T = it . 

v 

Periodic and Alternate Discharge. — (See 
Discharge, Periodic. Discharge, Alternat- 
ing^ 

Periodic Current, Power of The 

rate of transformation of the energy of a cir- 
cuit traversed by a simple periodic current. 




Fig. 420. Power of Periodic Current. — {Fleming!) 

If the thin line in the curve, Fig. 420, repre- 
sents the impressed electromotive force in an in- 
ductive circuit, and the thick line the correspond- 
ing current, then, at any instant, say at the point 
M, the rate at which energy is being expended on 
the circuit, is equal to the ordinate P M, multi- 
plied by the ordinate Q M. The mean power is 



the mean of all such products taken at points of 
time very near together. 

The power of a periodic current, or the work 
expended per second on such a circuit, is equal 
to half the product of the maximum values of the 
current, at any instant, and the maximum value 
of the impressed electromotive force, multiplied 
by the cosine of the angle of lag. 

Periodic Governor. — (See Governor, 
Periodic?) 

Periodically Decreasing* Discharge. — 

(See Discharge, Periodically Decreasing?) 

Periodicity.— The rate of change in the 
alternations or pulsations of an electric cur- 
rent. 

Periodicity of Auroras and Magnetic 
Storms. — (See Auroras atid Magnetic 
Storms, Periodicity of?) 

Permanency, Electric The prop- 
erty possessed by most metallic substances, 
while in the solid state, of retaining a constant 
electric conducting power at the same tem- 
perature. 

The electric permanency of hard drawn wire is 
small, since such wire becomes gradually an- 
nealed, and thus changed in its electric resist- 
ance. 

Matthiessen showed that some specimens of 
annealed German silver wire increased in their 
conducting power at the rate of about .02 per 
cent, yearly. 

Permanent Intensity of Magnetization. 

— (See Magnetization, Permane7it, Intensity 
of.) 

Permanent Magnet Voltmeter. — (See 
Voltmeter, Permanent Magnet?) 

Permanent State of Charge on Telegraph 
Line. — (See State, Per?na?ient, of Charge on 
Telegraph Li?ie.) 

Permeability Curve.— (See Cu7've, Per- 
meability?) 

Permeability, Magnetic Conducti- 

bility for lines of magnetic forces. 

The ratio existing between the magnetiza^ 
tion produced, and the magnetizing force pro- 
ducing such magnetization. 

If ju equals the permeability, B, the magnetiza- 



Per.] 



394 



[Phe. 



tion produced, or the intensity of magnetic induc- 
tion, and H, the magnetizing force; then, 



M = a 



The permeability of non-magnetic materials, 
such as insulators, or non-magnetic metals, such as 
copper, etc., is assumed to be practically equal to . 
that of air, or to unity. 

The magnetic permeability decreases as the 
magnetization increases. When a piece of iron 
has been magnetized up to a certain intensity, its 
permeability becomes less for any further magnet- 
ization ; or, the substance shows a tendency to 
reach magnetic saturation. In good iron, this 
limit is reached at about 125,000 lines of force to 
the square inch of zrea of cross section. 

The magnetic permeability varies greatly, not 
only with different specimens of iron, but also with 
the previous history of the iron, as to whether or 
not it has before been subjected to magnetization or 
demagnetization, and also as to whether the value 
of the permeability is taken while the magnetiza- 
tion is increasing or decreasing. 

Permeameter. — An apparatus devised by 
S. P. Thompson, for roughly measuring the 
magnetic permeability. 

Thompson's permeameter consists essentially of 
a rectangular piece of soft iron, provided with a 
slot, for the reception of the magnetizing coil. A 
hole bored in one end of the block serves to receive 
the bar or rod of iron whose permeability is to be 
determined. On the magnetization of the bar to 
be tested, the square root of the force required to 
detach the rod from the lower surface of the iron 
block, is a measure of the permeation of the lines 
of magnetic forces through its end faces. 

Permeance, Magnetic — Magnetic 

permeability. (See Permeability, Magnetic?) 

Permeating-, as of Lines of Force.— 

The passing of lines of force through a mag- 
netic substance. (See Per?neability, Mag- 
netic?) 

Permeation, Magnetic The pass- 
age of lines of magnetic force through any 
permeable substance. 

Permissive Block System for Railroads. 

— (See Railroads, Permissive Block System 

for.) 



Pfluger's Law.— (See Law, PJlugers) 

Phantom Wires. — (See Wires, Phantom.), 

Phase, Angle of Difference of, between: 
Alternating" Currents of Same Period 

The angle which measures the shift- 
ing of phase of a simple periodic current with 
respect to another due to lag or other cause. 

Phase, Shifting of, of Alternating Cur- 
rent A change in phase of current 

due to magnetic lag or other causes. 

Phase of Vibration. — (See Vibration, 
Phase of.) 

Phelps' Stock Printer.— (See Printer, 
Stock, Phelps .) 

Phenomena, Electro-Capillary — 

Phenomena observed in capillary tubes at 
the contact surfaces of two liquids. 

Where acidulated water is in contact with 
mercury, each liquid possesses a definite sur- 
face tension, and each a definite shape of sur- 
face. The two liquids, however; do not actually 
touch, there being a small interval or space be- 
tween them. This space acts as a minute accu- 
mulator. But the liquid and water, being different 
substances in contact, possess different potentials. 
Any cause which alters the shape of these con- 
tact surfaces, and consequently the extent of the 
spaces between them, necessarily alters the capa- 
city of the condenser, and consequently the dif- 
ference of potential. Therefore the mere shaking 
of the tube, or heating it, will produce electric- 
currents from the resulting differences of po- 
tential. Conversely, an electric current sent 
across the contact-surfaces will produce motion as 
a result of a change in the value of the surface 
tension. An electro-capillary telephone has been 
constructed on the former principle, and an 
electrometer on the latter. (See Electrometer, 
Capillary.) 

Phenomena, Porret — An increase 

in the diameter of a nerve fibre in the neigh- 
borhood of the positive pole when traversed 
by a voltaic current. 

When a voltaic current passes through fresh 
living substance the contents of the muscular fibre 
exhibit a streaming movement in the direction the 
current is flowing, viz., from the positive to the 



lh;.J 



395 



[Pho. 



negative. This causes the fibre to swell up or 
increase in diameter at the negative electrode. 

Pherope. — A name sometimes applied to 
a telephote. (See Telephote.) 

Phial, Leyden A name sometimes 

applied to a Leyden jar. (See Jar, Leyden.) 

Philosopher's Egg.— (See Egg, Philoso- 
pher's.) 

Phonautograph.— An apparatus for the 
automatic production of a visible tracing of 
the vibrations produced by any sound. 

Phonautographic apparatus consists essentially 
of devices by which the sound waves are caused 
to impart their to-and-fro movements to a dia- 
phragm, at the centre of which a pencil or tracing 
point is attached. The record is received on a 
sheet of paper, or wax, or on a smoked glass or 
other suitable surface. 

Leon Scott's Phonautograph, which is among 
the forms best known, consists of a hollow conical 




Fig 421. Scott 's Phonautograph. 

vessel A, Fig. 421, with a diaphragm of parch- 
ment stretched tightly like a drumhead over its 
smaller aperture B. A tracing point attached to 
the centre of the diaphragm, traces a sinuous 
line on the surface of a soot-covered cylinder C, 
that is uniformly rotated under the tracing point. 
As the cylinder is advanced a short distance with 
every rotation, a sinuous spiral line is traced on 
the surface. 

Phone. — A term frequently used for tele- 
phone. 

Phonic Wheel.— (See Wheel Phonic) 

Phonogram.— A record produced by the 
phonograph. (See Pho7iograph) 

Phonograph.— An apparatus for the re- 
production of articulate speech, or of sounds 



of any character, at any indefinite time after 
their occurrence, and for any number of times. 
In Edison's phonograph the voice of the 
speaker, received by an elastic diaphragm of thin 
sheet iron or other similar material, is caused to 
indent a sheet of tin-foil placed on the surface of 
a cylinder C, Fig. 422, that is maintained at a 
uniform rate of rotation by the crank at W. In 




Fig. 422. 

the form shown in Fig. 422, the motion is by hand. 
In a later improved form the cylinder is driven by 
means of an electric motor or by clockwork. 

In order to reproduce the speech or other 
sounds the phonogram record is placed on the 
surface of a cylinder similar to that on which it 
was received (or is kept on the same surface), 
and the tracing point, placed at the beginning of 
the record and being maintained against it by 
gentle pressure, is caused, by the rotation of 
cylinder, to follow the indentations of the phono- 
gram record. As the point is thus moved up and 
down the hills and hollows of the record surface, 




Fig. 423. Edison's Improved Phonograph. 

the diaphragm, to which it is attached, is given to- 
and-fro motions that exactly correspond to the 
to-and-fro motions it had when impressed origin- 
ally by the sounds it recorded on the phono- 
gram record. A person listening at this dia- 



Pho.] 



[Pho. 



phragm will therefore hear an exact reproduction 
of the sounds originally uttered. 

In this manner the voices of relatives, dis- 
tinguished singers or statesmen can be preserved 
for future generations. 

In Edison's improved phonograph the record 
surface consists of a cylinder of hardened wax. The 
rotary motion of the cylinder is obtained by means 
of an electric motor. Two diaphragms are used, 
one for recording, and one for reproducing the 
sound waves. As shown in Fig. 423, the record- 
ing diaphragm is in position against the cylinder. 
The recording diaphragm is made of malleable 
glass. The reproducing diaphragm is formed of 
bolting silk covered with a thin layer of shellac. 

In the Graphophone of Bell and Tainter the 
point attached to the diaphragm is caused to cut 




Fig. 424. Bell and Tainter 's Graphophone. 
or engrave a cylinder of hardened wax. Two 
separate diaphragms are employed, one for speak- 
ing, and the other for hearing. 

The recording surface is made of a mixture of 
beeswax and paraffine. A uniformity of rotation of 
the cylinder is obtained by means of a motor pro- 
vided with a suitable governor. An ordinary con- 
versation of some five minutes, it is claimed, can 
be recorded on the surface of a cylinder 6 inches 
long and 1^- inch in diameter. 

In the Gramophone of Berliner, a circular plate 
of metal, covered with a film of finely divided oil 



or grease, receives the record in a sinuous, spiral 
line. This record is subsequently etched into the 
metal by any suitable means, or is photographic- 
ally reproduced on another sheet of metal. 

Glass covered with a deposit of soot is some- 
times employed for the latter process. The ap- 
paratus is shown in Fig. 425, as arranged for the 
reproduction of speech. 

In Mr. Berliner's apparatus, the record surface 
is impressed by a point attached to the trans- 
mitting diaphragm, in a direction parallel to the 
record surface, and not, as in the instrument of 
Mr. Edison, in a direction at right angles to the 
same. This method would appear to be the best 
calculated for a more exact reproduction of ar- 
ticulate speech, since it permits comparatively 
loud speaking or singing, without interfering 




Fig. 42s 



Gramophone. 



with the quality of the reproduced sounds. Since 
the resistance to indentation, or vertical cutting, 
increases more rapidly than the increase in the 
amplitude of vibration of the cutting point, it 
follows that the louder the sounds recorded by the 
phonograph or graphophone, the less complete 
would be the quality of the reproduced sounds, 
or the less the probability of the peculiarities of 
the speaker's voice being recognized. In order 
to avoid this, the speaker in the phonograph and 
the graphophone speaks in an ordinary conversa- 
tional tone only. (See Vibration or Wave, Am- 
plitude of ) 

For purposes of dictation, and, indeed, most 
commercial purposes, this is rather an advantage 
than otherwise. 

Phonograph Record. — (See Record, 
Phonography 

Phonoplex. — Literally sound folds. 

A system of telegraphy. (See Telegraphy, 
Phonoplex.) 



Pho.] 



397 



[Pho. 



Phonoplex Telegraphy. — (See Telegra- 
phy, Phonoplex?) 

Phonopore. — A modified form of har- 
monic telegraph. 

Phonozenograph. — An instrument devised 
by De Feltre to indicate the direction of a 
distant sound. 

A Deprez-D' Arson val galvanometer, a Wheat- 
stone's bridge, and a microphone of peculiar con- 
struction, are placed in the circuit of a voltaic 
battery and a receiving telephone. The observer 
determines the direction of the distant sound by 
means of the sounds heard under different condi- 
tions in the telephone. 

Phosphoresce. — To emit phosphorescent 
light. 

Phosphorescence. — The power of emitting 
light, or becoming luminous by simple ex- 
posure to light. 

Bodies that possess the property of phosphor- 
escence, when exposed to a bright light acquire 
the power, when subsequently carried into the 
dark, of continuing to emit light, for periods 
varying from a few seconds to several hours. 
The diamond, barium and calcium sulphides, 
dry paper, silk, sugar, and compounds of ura- 
nium, are examples of phosphorescent substances. 

The effects of phosphorescence appear to be 
due, in some cases, to sympathetic vibrations set 
up in the molecules of the phosphorescent body 
by the exciting light. (See Vibrations, Sympa- 
thetic.) 

In other cases, however, that are not exactly 
understood, the wave length of the emitted light 
is more rapid than that of the exciting light. 

The fire-fly, the glow-worm, and decaying 
animal or vegetable matter, exhibit a species of 
phosphorescence that appears to be due to the ac- 
tual oxidation or gradual burning of a peculiar, 
specific, chemical substance. 

Phosphorescence may therefore be divided into 
two classes, viz. : 

(I.) Physical phosphorescence, or that produced 
Ijy the actual impact of light, and, 

(2.) Chemical phosphorescence, or that caused 
by actual chemical combination or combustion of 
a specific substance. This is sometimes called 
spontaneous phosphorescence. 

Physical phosphorescence may be produced in 
a variety of ways, viz.: 



(1.) By an Elevation of Temperature: 
A variety of fluorspar, called chlorophane, 
shines with a beautiful greenish blue light when 
heated to less than a red heat. Here the non- 
luminous rays are apparently transformed into 
luminous rays. 

A phosphorescent substance like fluorspar 
eventually loses its ability to phosphoresce. It 
regains it, however, on exposure to the light, i. e., 
if such an exhausted body be exposed to sunlight it 
again phosphoresces on exposure to non-luminous 
heat. The light emitted, during phosphorescence 
by heat, is, probably, wholly du^ to potential 
energy acquired during exposure to the light. 
(See Luminescence.) The phosphorescence by 
heat exhibited by fluorspar is sometimes called 
fluorescence. It is preferable, however, to call 
the phenomena phosphorescence. (See Fluores- 
cence.) 

(2.) By Mechanical Effects: 

The flashes of light emitted during the attri- 
tion or friction of some bodies, when not traceable 
directly to electricity, are, most probably, to be 
ascribed to phosphorescence. 

(3.) By Molecular Bombardment. 

The molecular bombardment due to the mole- 
cules of residual gas shot off from the negative 
electrode of an exhausted receiver through which 
an electric discharge is passing, produces many 
brilliant effects of phosphorescence. 

(4.) By Electricity. 

An electric spark produces phosphorescence in 
such substances as canary glass, solution of sul- 
phate of quinine, etc., etc. 

(5.) Exposure to Sunlight, or, in fact, to any 
light. 

The different rays of the sun are not equally 
able to excite phosphorescence. As a rule the 
violet or ultra violet rays excite the greatest phos- 
phorescence. The light excited is often, though 
not always, of a greater wave length than the 
exciting light. 

Phosphorescent paints for rendering the posi- 
tion of a push button, electric call, match safe, 
gas pendant or some other similar object visible 
at night, consist essentially of sulphides of cal- 
cium or barium, or of mixtures of the same. 

Phosphorescence, Chemical A 

variety of phosphorescence, in which the emit- 
ted light is produced by the actual combustion 



398 



[Pho. 



of a specific chemical substance by the oxygen 
of the air. 

Chemical phosphorescence is seen in the fire- 
fly and the glow-worm. (See Phosphorescence.) 

Phosphorescence, Electric Phos- 
phorescence caused in a substance by the 
passage of an electric discharge. 

The phosphorescent material is placed in an 
exhausted glass tube, as shown in Fig. 426, and 
submitted to the action of a series of discharges, 
as from a Ruhmkorff coil, or Holtz machine. 
The violet-blue tight of such discharge is very 
efficient in producing phosphorescence. Phosphor- 
escence is thus effected by subjecting the phos- 
phorescent material to the molecular bombard- 
ment which is produced by such discharges in a 
high vacuum. (S~e Bombardment, Molecular.) 




Fig. 426. Electric Phosphorescence. 

Phosphorescence, Physical Phos- 
phorescence produced in matter by the actual 
impact of light waves resulting in a vibratory 
motion of the molecules of sufficient rapidity 
to cause them to emit light. 

Physical phosphorescence is distinguished from 
chemical phosphorescence in that in the former 
the energy required to produce molecular vibra- 
tions is imparted by the light to which the phos- 
phorescent body is exposed, while in chemical 
phosphorescence the energy producing the light 
is derived from the chemical potential energy 
of the specific substance burned. (See Phosphor- 
escence. ) 

Phosphorescent — Possessing the proper- 
ties or qualities of phosphorescence. 

Phosphorescing 1 . — Emitting phosphores- 
cent light. (See Phosphorescence?) 

Phosphorescope. — An apparatus for meas- 
uring the phosphorescent power of any sub- 
stance. (See Phosphorescence.) 



Phosphorus. Electric Smelting of 

— An electric process for the direct production, 
of phosphorus. 

In the electric smelting of phosphorus, the 
crude material, consisting of a mixture of bones or 
animal phosphates and carbon, is fed into a space 
between two electrodes connected to the poles of 
a source of powerful alternating currents. The 
apparatus is similar in general to the Cowles fur- 
nace for the reduction of aluminium. The heat 
produced by the alternating currents decomposes 
the phosphates, and the volatilized phosphorus 
is condensed in suitable chambers. 

Photochronograph. — An electric instru- 
ment for automatically recording the transit 
of a star across the meridian. 

In a small camera connected with the eye-piece 
of the transit instrument is placed a sensitized 
plate. 

A sidereal clock has an electric attachment to 
its pendulum, so made that a shutter alternately 
exposes and conceals the photographic plate, and 
thus permits the image of a star to be formed on 
the plate at intervals during its passage across 
the field of the telescope. An image of the spider 
lines is afterwards fixed on the plate by the light 
of a lamp, held for a few moments before the ob- 
ject glass of a telescope. A shutter is provided, 
by means of which this light is prevented from 
falling on the trail of the star across the field of 
the glass. In this manner the time of passage of 
the star across the meridian is automatically re- 
corded on the photographic plate. 

The photochronograph is also adapted for 
similarly automatically recording the transit or 
passage of any heavenly body across any imagin- 
ary line in the heavens. 

Photo-Electric Cell.— (See Cell, Photo- 

Electric.) 

Phot o-Electricity. — ( See Electricity, 
Photon 

Photo-Electromotive Force. — (See Force, 
Electromotive, Photo?) 

Photometer. — An apparatus for measuring 
the intensity of the light emitted by any 
luminous source. 

There are various methods for measuring the 
intensity of a beam of light passing through any 
given space, or emitted from any luminous 



Pho. 



399 



[Pho. 



source; these methods are embraced in the use 
of the following apparatus: 

(I.) Calorimetric Photometer, in which the light 
to be measured is absorbed by the face of a 
thermo-electric pile, and the electric current 
thereby produced is carefully measured. Since 
obscure radiation or heat will also thus produce 
an electric current, it is necessary first to absorb 
all the heat by passing the beam of light through 
an alum cell. 

(2.) Actinic, or Chemical Photometers, in which 
the intensity of the light is estimated by a com- 
parison of the depth of coloration produced on a 
fillet of photographic paper under similar con- 
ditions of exposure to a standard light, and the 
light to be measured. 

The combination of pure hydrogen and chlorine, 
or the decomposition of pure mercurous chloride, 
have been employed for the purpose of determin- 
ing the intensities of two lights by measuring the 
amount of chemical action effected. 

(3.) Shadow Photometers, in which a shadow 
produced by the light to be measured is compared 
with a shadow produced by a standard candle. 
(See Candle, Standard.) 





Fig. 4 2 "J. The Shadow Photometer. 

Rumford's photometer, shown in Fig. 427, is 
an example of this iorm of instrument. The 
standard candle, shown at L, casts a shadow C", 
of an opaque rod C, on the screen at B. 

The light to be measured L', is moved away 
from the screen until its shadow C, on the screen 
at A, is judged by the eye to be of the same 
depth. The distance between the screen and the 
lights is then measured in straight lines. The 
relative intensities of the two lights are then pro- 
portional to the squares of their distances. If, for 
example, the candle be at 10 inches from the 
screen, and the lamp at 40 inches, then the 
intensities are as io 2 : 40- or as 100 : 1,600, or the 
lamp is a 16 candle-power lamp. 



This photometer is based on the fact that the 
shadow of each source is illumined by the light 
of the other source. 

These results are more accurate if the two 
shadows are adjoining or nearly adjoining. 

(4. ) Translucent -Disc Photometers. —The light 
to be measured and a standard c indie are placed 
on opposite sides of a sheet of paper the centre of 
which contains a grease spot. The standard 
candle is kept at a fixed dis'ance from the paper 
and both it and the paper are moved towards or 
from the light to be measured until both sides of 
the paper are adjudged to be equally illumined. 

In Bunsen's photometer a vertical sheet of 
paper with a grease spot at its centre, is exposed 
to the illumination of a standard candle on one 
side, and the light to be measured on the other. 

The sheet of paper is placed inside a dark box 
provided with two plane mirrors placed at such 
an angle to the paper that an observer can readily 
see both sides of the paper at the same time. 

This box can be slid along a graduated, hori- 
zontal scale towards, or from, the light to be 
measured, and carries with it the standard candle 
mounted on it at a constant distance of 10 inches. 
If the box is too near the light to be measured, 
the grease spot appears brighter on the side of the 
sheet of paper nearest the candle. If too near 
the candle, it appears brighter on the side of the 
sheet of paper nearest the light to be measured. 
The position in which the spot appears equally 
bright on both sides, is the position in which both 
sides of the paper are equally illumined, and the 
relative intensities of the two lights are then 
directly as the squares of their distances from the 
sheet of paper. 

Shadow, and translucent-disc photometers 
being dependent on equal illumination, are re- 
liable only when the color of the lights compared 
is the same. For the determination of the photo- 
metric intensity of very bright lights, the standard 
candle is replaced by a carcel lamp, a standard 
gas jet, or by the light emitted by a given mass 
of platinum, heated to incandescence by a given 
current of electricity. (See Lamp, Carcel. Gas- 
yet, Carcel Standard. Light, Platinum Stand- 
ard.) 

Preece's photometer belongs to the class of 
translucent disc photometers. A tiny incandes- 
cent lamp is placed in a box, the top of which has 
a white paper screen on which is a grease sput. 
The box is placed in the street where the intensity 
of illumination is to be measured, and the inten- 



Pko. 



400 



[Pho. 



sity of the light of the incandescent lamp is 
varied until the grease spot disappears. The 
current of electricity then passing through the 
incandescent lamp acts as the measure of the 
illumination. 

In the case of the shadow photometer, or of 
Bunsen's photometer, if the intensity of illumina- 
tion is the same, the relative intensities of the two 
lights may be determined as follows: 

Calling I, and i, respectively the relative inten- 
sities of the standard light, and the light to be 
measured, and D, and d, their respective dis- 
tances from the screen, then 

I : i : : D2 : d 2 , or I X d2 = i x D 2 ; 



thatis,i = l(-Q. 



Or, the intensity of the light to be measured is 

(d 2 \ 
— - J times the intensity of the standard light. 

If, for example, D and d, represent 10 and ioo 
inches, respectively, the intensity of i, is ioo times 
the intensity I, the standard light. 

(5.) Dispersion Photometers. -A class of pho- 
tometers in which, in order to more readily com- 
pare or measure a very bright or intense light, 
like that of an arc lamp, the intensity of the light 
is decreased by dispersion a readily measurable 
amount. 

Ayr ton &> Perry" 1 s Dispersion Photo?neter. — A 
photometer in which, in order to bring an in- 
tensely bright light, like an electric arc light, to 




Fig. 428. Ayrton &* Perry's Dispersion Photometer. 

such an intensity as will permit it to be readily 
compared with a standard candle, its intensity is 
weakened by its passage through a diverging 
(concave) lens. 

Ayrton & Perry's dispersion photometer is 
shown in two different positions, Figs. 428 and 
429. The apparatus is supported on a tripod 
stand E, arranged so as to obtain exact leveling. 



A plane mirror H, movable around a pin placed 
directly under its centre, can be rotated and thus 
reflect the light after its passage through the 
diverging lens, while still maintaining its distance 
from the electric light. 

The horizontal axis of this mirror is inclined 
45 degrees to its reflecting surface in order to 
avoid errors arising from varying absorption at 
different angles of reflection. 

The inclination of the beam to the horizontal 
is indicated by means of an index attached to the 
mirror and moving over the graduated circle G. 

A black rod A, casts its shadow on a screen of 
white blotting paper B. A standard candle, 
placed in the holder D, casts its shadow alongside 
the shadow cast by the electric light. The lens 
is now displaced until the shadow of the electric 
light is of the same intensity as that of the candle, 
when viewed successively through sheets of red 
and green glass. 

A graduated scale serves to mark the distances 
of the candle and the lens, respectively, from the 
screen, from which data the intensity of the 
electric light may be calculated. 




Fig. 42 Q. Ayrton and Perry's Dispersion Photometer. 

(6.) Selenium Photometers. — Instruments in 
which the relative intensities of two lights are de- 
termined by the variations produced in a selenium 
resistance. 

In Siemens' Selenium photometer a selenium 
cell is employed in connection with an electric 
circuit for determining the intensity of light. 

The tube A B, Fig. 430, is furnished at A, with 
a diaphragm, and at B, with a selenium plate, 
connected by wires G G, with the circuit of a 
battery and a galvanometer. 

A graduated scale L M, bears the standard 
candle N. The tube A B, is capable of rotation 
on the vertical axis F. A reflecting mirror gal- 
vanometer is used in connection with the selenium 
photometer. The light to be measured is placed 



Pho.] 



401 



[Pho. 



at right angles to the scale L M, and the tube A 
B, directed towards it, and the galvanometer de- 
flection compared with the deflection obtained 
when turned towards the standard candle. 

(7.) Gas-jet Photometers. — Instruments in 
which the candle-power of a gas jet is determined 
by measuring the height at which the jet burns 
when under unit conditions of volume and press- 
ure of gas consumed. 




Fig. 430. Siemens' Selenium Photometer. 

In determining the candle-power of an intense 
light like the electric arc light, a large gaslight 
is used instead of a standard candle, and the 
photometric power of this gaslight is carefully 
determined by comparison with a gas-jet photom- 
eter. (See Jet, Gas, Car eel Standard.) 

Photometer, Actinic A photom- 
eter in which the intensity of any light is meas- 
ured by the amount of chemical decomposi- 
tion it effects. (See Photometer.) 

In some actinic photometers the intensity of the 
light to be measured is determined by the com- 
parison of the depth of coloration of a sensi- 
tized film under similar conditions of exposure 
to a standard light and the light to be measured. 

A pho- 



Photometer, Calorimetric — 

tometer in which the light to be measured is 
absorbed by the face of a thermo-electric pile, 
and the intensity of the light estimated from 
the strength of the electric current thereby 
produced. 

In order to avoid the error arising from the 
current produced from the absorption of the ob- 
scure radiation from the light, all the heat is first 
absorbed by passing the light through an alum 
cell. (See Photometer.) 

— A photom- 



PHotometer, Chemical — 

eter in which the intensity of the light to be 



measured is determined from the amount of 
chemical action effected in a given time. 

Photometer, Dispersion A photom- 
eter in which the light to be measured is de- 
creased in intensity a known amount so as to 
more readily permit it to be compared with a 
standard light of much smaller intensity. 
(See Photometer^) 

Photometer, Electric An electrical 

instrument for measuring the intensity of 
illumination. 

A form of electric photometer invented by C. 
R. Richards depends for its indications on the 
variations that occur in the resistance of a wire on 
change of temperature. An iron wire, whose 
change of temperature is utilized for measuring 
the intensity of any light to whose radiations it is 
opposed, is cuvered by a deposit of lampblack. 
On exposure to the light whose intensity is to 
be measured, the light is absorbed by the lamp- 
black and an increase in temperature occurs. 

In order to get rid of the heat rays that are 
associated with the light rays, the rays before 
falling on the soot-covered wire are caused to pass 
through a solution of alum ; the intensity of the 
light is then calculated by reference to the change 
in the resistance of the soot-covered wire, which 
is made one of the arms of a Wheatstone bridge. 

Photometer, Gas-Jet — A photom- 
eter in which the candle-power of a gas jet is 
estimated from a measurement of the height 
at which the jet burns under unit conditions 
of volume and pressure. (See Photometer^) 

Photometer, Jet An apparatus for 

determining the candle power of a luminous 
source by means of the height of a jet of the 
gas, whose candle-power is being determined, 
when burning under constant conditions as 
to pressure, etc. (See Jet, Gas, Carcel 
Standard.) 

Photometer, Selenium A photom- 
eter in which the intensity of a light is esti- 
mated by the comparison of the changes in 
the resistance of a selenium resistance suc- 
cessively exposed under similar conditions to 
this light and to a standard light. (See 
Photometer^) 

Photometer, Shadow A photom- 
eter in which the intensity of the light to be 



Pko.] 



402 



[Pho. 



measured is estimated by a comparison of 
the distances at which it and a standard light 
produce a shadow of the same intensity. 
(See Photometer) 

Photometer, Translucent Disc A 

photometer in which the light to be measured 
is placed on one side of a partly translucent 
and partly opaque disc, and a standard can- 
dle is placed on the opposite side, and the in- 
tensity of the light estimated by the distances 
of the light from the disc when an equal illu- 
mination of all parts of the disc is obtained. 
(See Photometer) 

When the illumination of the opposite sides of 
such a disc is equal, the relative positions of the 
transparent and opaque portions of the disc are 
indistinguishable. 

Photometer, Yarley's A form of 

photometer in which the intensity of the light 
to be measured is determined from the rel- 
ative openings of two concentric circular 
diaphragms placed in two rotating discs, and 
through which the standard light and the 
light to be measured respectively pass. 

The general arrangement of Varley's photo- 
meter is shown in Fig. 431. The concentric cir- 




Fig- 43 '*• Varley's Photometer. 

cular apertures extend circumferentially 180 de- 
grees, and are reversed so that when one half 



ring is fully open, the r ther is completely closed; 
or, if one ring, say the outer, is opened 160 de- 
grees, the inner is opened 20 degrees. The 
quantity of light then which passes through the 
outer ring from the light to be measured is eight 
times that passed through the inner ring. The 
circle is divided into 2,000 parts, instead of into 
360 degrees, and, by means of a vernier, these 
parts are further divided into 10 parts, permitting 
a reading of the 20,000 divisions. 

Two collimeters placed in front of the disc, 
project a disc with a black centre, and a luminous 
spot respectively. The discs are regulated until 
the light projected on the screen produces a uni- 
form disc. This is readily ascertained, since if 
one or the other predominate, a disc with gray 
spot, or a gray marginal ring with a bright spot, 
will appear. 

The general appearance of the circular dia- 
phragm, corresponding to different relative posi- 
tions of the two discs, is shown in Fig. 432. 

Fig. 432. Circular Diaphragm of Varley's Photometer. 

Photometric. — Of or pertaining to the 
photometer. (See Photometer) 

Photometrically. — In a photometric man- 
ner. 

Photophone. — An instrument invented by 
Bell for the telephonic transmission of artic- 
ulate speech along a ray of light instead of 
along a conducting wire. 

A beam of light, reflected from a diaphragm 
against which the speaker's voice is directed, is 
caused to fall on a selenium resistance inserted in 
the circuit of a voltaic battery, and a telephone. 
The changes thus effected in the resistance of the 
circuit by the varying amounts of light reflected on 
the selenium resistance from the diaphragm, while 
moving to-and-fro under the influence of the speak- 
er's v 'Ice, produce in the receiving telephone a 
series of to-and fro movements similar to those im- 
pressed on the transmitting diaphragm. One lis- 
tening at the telephone can hear whatever has been 
spoken in the neighborhood of the transmitting 
diaphragm. Telephonic communication can, 
therefore, by such means be carried on along a 



Pho.] 



403 



[Pie. 



ray or beam of light, theoretically through any 
distance. (See Resistance, Selenium.) 

A block of vulcanite or of certain other sub- 
stances may be used as the receiver, since it has 
been discovered that a rapid succession of flashes 
of light produces an audible sound in small masses 
of these substances. 

The term sonorescence has been proposed for 
the property possessed by such substances of 
emitting sounds when subjected to such inter- 
mittent flashes of light. (See Sonorescence.') 

Photophore, Trouve's — An appa- 
ratus in which the light of a small incandescent 
electric lamp is employed for purposes of 
medical exploration. 

A small incandescent lamp is placed in a tube 
containing a concave mirror and a converging 
lens. 

Photo-Telegraphy. — The electric produc- 
tion of pictures, writing, charts or diagrams 
at a distance. 

Photo -Telegraphy is sometimes called telepho- 
tography; it is a species of fac-simile telegraphy. 
(See Telegraphy, Eac-Si?nile. Telephotography .) 

Photo- Yoltaic Effect.— (See Effect, Photo- 
Voltaic^) 

Physical Change. — (See Change, Phy- 
sical^) 

Physical Phosphorescence. — (See Phos- 
phorescence, Physical) 

Physiological. — Pertaining to physiology. 

Physiological Rheoscope. — (See Rheo- 
scope, Physiological.) 

Physiologically. — In a physiological man- 
ner. 

Physiology, Electro — The study of 

electric phenomena of living animals and 
plants. 

Living animals and plants present electric 
phenomena, due to the electricity naturally pro- 
duced by them. It is the province of electro- 
physiology to ascertain the causes and effects of 
these phenomena. 

Piano, Electric A piano in which 

:he strings are struck by hammers actuated 
by means of electro-magnets, instead of by 
the usual mechanical action of levers. 



An electric piano-action is mainly useful in per- 
mitting the instrument to be played at any dis- 
tance from the key-board, it is also of value 
from the ease it affords in recording the pieces 
played. 

It fails, however, to properly preserve the vari- 
ous modulations of force so requisite for brilliant 
instrumentation. 

Pickle. — An acid solution in which me- 
tallic objects are dipped before being gal- 
vanized, or electroplated, in order to 
thoroughly cleanse their surfaces. 

The pickle used for the preparation of iron for 
galvanization is a weak solution of sulphuric acid 
in water. Various acids, or acid liquids, are em- 
ployed for insuring the thorough cleansing of 
metallic surfaces so necessary in order to ensure 
an even, uniform, adherent coating of metal by 
the process of electroplating. (See Plating, 
Electro ) 

Piece, Magnetic Proof A para- 
magnetic rod, ellipsoid or sphere employed 
for ascertaining the distribution of magnetism 
over a magnet by the force required to de- 
tach the same. (See Paramagnetic) 

Prof. S. P. Thompson points out the fact 
that the presence of the proof-piece so alters the 
distribution of magnetism on the magnet to be 
measured as to render this method unreliable. 
He also shows that the force required for detach- 
ment depends on the magnetic permeability of 
the proof-piece, as well as on its shape and its 
position in the magnetic circuit. 

Pieces, Month Openings into air 

chambers, generally circular in shape, placed 
over the diaphragms of telephones, phono- 
graphs, gramophones or graphophones to 
permit the ready application of the mouth in 
speaking, so as to set the diaphragm into 
vibration. 

The mouth-piece may be also utilized by the 
ear of an observer listening so as to be affected 
by its vibrations. 

Pieces, Pole, of Dynamo-Electric 31a- 

chine Masses of iron connected with 

the poles of the field magnet frames of 
dynamo-electric machines, and shaped to 
conform to the outline or contour of the 
armature. 



PiL] 



40i 



[PIL 



The pole pieces are made in a variety of forms, 
but in all cases are so shaped as to conform to the 
outline of the space in which the armature rotates. 

The pole pieces are brought as near as possible 
to the armature, so as to increase the intensity of 
the magnetic induction. The intervening air 
space should be as thin as possible, but of as large 
an area as convenient. 

The opposite pole pieces should not have their 
extensions brought too near together, as this will 
permit of serious loss through magnetic leakage. 
The distance between them should be as many 
times the depth of the armature windings as 
possible. (See Leakage, Magnetic.) 

Rounded edges are preferable to sharp edges 
for the same reason. 



-A voltaic pile or battery 



Pile, Dry — 

consisting of numerous cells, the voltaic 
couple in each of which consists of sheets of 
paper covered with zinc-foil on one side and 
black oxide of manganese on the other. 

Various modifications of the above form have 
been made. 

The term dry-pile is a misnomer, since all such 
piles contain substances moistened by liquid 
electrolytes. 

Pile, Muscular, Matteucci's A vol- 
taic battery or pile, the elements of which are 
formed of longitudinal and transverse sections 
of muscle alternately connected. 

Matteucci's experiments appear to show that 
the lower the animal is in the scale of creation, 
the stronger is the current produced, and the 
longer its duration. Du Bois-Reymond has 
shown that the muscular current is not due to 
contact, but to the differences of electric poten- 
tial naturally possessed by the muscles then- 
selves. 

The nerves also possess the power of producing 
differences of electromotive force, and hence cur- 
rents. (See Electrolonus. ) 

Pile, Thermo, Differential A ther- 
mopile in which the two opposite faces are 
exposed to the action of two nearly equal 
sources of heat in order to determine accu- 
rately the differences in the thermal intensities 
of such sources of heat. 

Pile, Thermo-Electric A number 

of separate thermo-electric couples, united in 



series, so as to form a single thermo-electric 
source. (See Couple, Thermo-Electric^) 

A thermo-electric pile is sometimes called a. 
thermo-electric battery. 

Fig- 433 shows Nobili's thermopile, in which- 
a number of bismuth- 
antimony thermo-elec- 
tric couples connected 
in a continuous se- 
ries, as shown par ly 
in Fig. 434, are insu- 
lated from one another, 
except at their junc- 
tions, and packed in a 
metallic box, supported 
as shown in Fig. 433. 
The free terminals of 
the series are con- 
nected to binding posts. 




Fig- 433> 



Thermo- Electric 
Pile. 

Differences of tem- 
perature between the two faces of the pile, where 
the junctions are exposed, result in a difference 
of potential equal to the sum of the differences of 
potential of all the thermo-electric couples. 



a+ 



A careful inspec- 
tion will show that 
the junctions are 
formed successively 
at opposite faces of 
the pile, so that if 
the junctions be 
numbered succes- 
sively, the even junc- 
tions will come at Fig. 434. Series -Connected 
one face, and the Thermo-Electric Couples, 

odd junctions at the other. This is necessary 
in order to permit all the thermo-electric couples 
to add their differences of potential ; for, if, as- 
in Fig. 435, a thermo-electric chain be formed, 





Fig. 435- Thermo-Electric Circuit. 

no currents will result from equally heating any 
two consecutive junctions J, J, of the metals A 
and B, since the electromotive forces so produced 
oppose each other. 

Thermopiles have been constructed by 
Clamond, of couples of iron and an alloy of zinc 
and antimony, of sufficient power to produce a 
voltaic arc whose illuminating power equaled 40 



Pil.] 



405 



[Pla. 



carcel burners. Many practical difficulties exist 
which will have to be surmounted, however, before 
such piles can be employed as commercial electric 
sources. 

— A battery consisting 



-A bolt by means 



Pile, Yoltaic — 

of a number of voltaic couples connected so 
as to form a single electric source. 

A form similar to Volta's original pile, consist- 
ing of alternate discs of copper and zinc, separated 
from each other by discs of wet cloth, and piled 
on one another, so as to form a number of separate 
voltaic couples connected in series, is shown in 
Fig. 436. The thick plates marked Zn, are of 
zinc ; the copper plates, marked Cu, are much 




Fig. 436. Voltaic Pile. 

thinner. The discs of moistened cloth are shown 
at d d. One end of such a pile would then be 
terminated by a plate of copper, and the other 
by a plate of zinc. The copper end forms the 
positive electrode, and the zinc end the negative 
electrode. (See Cell, Voltaic.) 

Pilot Lamp.— (See Lamp, Pilot.) 

Pilot Transformer. — (See Transformer, 

Pilot.) 

Pilot Wires.— (See Wires, Pilots 




Fig. 4 3 J. Insulator 
fin. 



Pin, Insulator — 

of which an insulator is attached to the tele- 
graphic support or arm. 

The insulator pins or bolts are generally fixed to 
the insulator by means of 
screw threads turned on 
their ends. They are then 
cemented to the insulators by 
any suitable moisture-proof 
cement. 

The pin and insulator con- 
nected to one another by 
means of a screw thread are 
shown in Fig. 437. 

Pin, Switch A 

metallic pin or plug pro- 
vided for insertion in a 
telegraphic switch board. 
A form of switch pin is 
shown in Fig. 438. The 
metallic end is conical in 
form, and is provided with 
two longitudinal slots at 
right angles to each other in 
order to insure a light spring connection with 
the metallic contact plate in which the pin is in- 
serted. 

Pith. — A light, cellular material, forming the 
central portions of most exogenous plants. 

An excellent pith, suitable for 
electrical purposes, is furnished by 
the dried interior of the elder-berry 
stick. 

Pith Ball.— (See Balls, Pith.) 

Pith - Ball Electroscope. — 

(See Electroscope, Pith-Ball.) 

Pivot Suspension. — (See Sus- 
pension, Pivot.) 

Plain-Pendant Argand Elec- 
tric Burner. — (See Burner, 
Plain-Pendant Electric^) 

Plain-Pendant Electric Burnei 

Burner, Plain-Pendant Electric.) 

Plane Angle. — (See Angle, Plane.) 

Plane, Proof A small insulated 

conductor employed to take test charges from 
the surfaces of insulated, charged conductors. 




Fig. 438. 

Switch Pin. 



(See 



Pla,] 



406 



[Pla. 



The proof-plane is used in connection with 
some form of electrometer. (See Balance, Cou- 
lomb 1 s Torsion.) 



Plane, Proof, Magnetic 



-A small 



coil of wire placed in the circuit of a delicate 
galvanometer, and used for the purpose of 
exploring a magnetic field. 

When the coil is suddenly inverted in a mag- 
netic field, if a long-coil galvanometer provided 
with a heavy needle is used, the number of lines 
of force which pass through the area of cross-sec- 
tion of the coil will be proportional to the sine of 
half the angle of the first swing of the needle. 

Plant. — A word sometimes used for in- 
stallation, or for the apparatus required to 
carry on any manufacturing operation. 

An electric plant includes the steam engines 
or other prime motors, the generating dynamo or 
dvnamos, the lamps and other electro-receptive 
devices, and the circuits connected therewith. 

Plant Electricity. — (See Electricity, 
Plant. Plants, Electricity of.) 

Plants, Electricity of Electricity 

produced naturally by plants during their vig- 
orous growth. 

DuBois-Reymond and others have shown that 
plants while in a vigorous vital state are active 
sources of electricity. 

If one of the terminals of a galvanometer be 
inserted into a fruit near its stem, and the other 
terminal into the opposite part of the fruit, the 
galvanometer at once shows the presence of an 
electric current. 

Buff has shown that the roots and interior por- 
tions of plants are always negatively charged, 
while the flowers, fruits and green twigs are posi- 
tively charged. 

Plant tissue or fibre, like the muscular fibre of 
animals, exhibits in many cases a true contraction 
on the passage through it of an electric current. 
This is seen in the Mimosa sensitiva, or Sensitive 
Fern, in the Venus' Fly-Trap, and in several other 
species of plants. 

Pouillet concludes from numerous observations 
that the free positive electricity of the atmosphere 
is partly due to the vapors disengaged by grow- 
ing plants. 

The peculiar geographical distribution of thun- 
der storms, however, does not favor this assump- 



tion. (See Storm, Thunder, Geographical Dis- 
tribution of.) 

Plastics, Galvano A term some- 
times employed for electrotyping, that is 
where the deposits are sufficiently thick to 
permit of ready separation from the object 
which forms the mould. 

Literally, the cold moulding or shaping of 
metals by electrotyping. (See Plating, Elec- 
tro. Metallurgy, Electro?) 

The word galvano-plastics is sometimes used 
as synonymous with electrotyping, electro-plat- 
ing, or electro-metallurgy generally. 

— The art of elec- 



Plastics, Hydro 



trically shaping or depositing metals in the 
wet by electrotyping. (See Plastics, Gal- 
vano?) 

Plate, Arrester, of Lightning Protector 

That plate of a lightning protector 

which is directly connected with the circuit 
to be protected, as distinguished from the plate 
that is connected with the ground. (See 
Arrester, Lightning?) 

Plate Condenser. — (See Condenser, Plate?) 
Plate, Ground, of Lightning Arrester 

— That plate of a comb lightning arrester 
which is connected to the earth or ground. 
(See Arrester, Lightning, Comb?) 

Plate, Negative, of Storage Cell 

That plate of a storage cell which, by the 
action of the charging current, is converted 
into or partly covered with a coating of spongy 
lead. 

That plate of a storage battery which is 
connected with the negative terminal of the 
charging source, and which is therefore the 
negative pole of the battery on discharging. 

The usage is the reverse of that in the case of 
the primary battery. 

Plate, Negative, of Yoltaic Cell 

The electro-negative element of a voltaic 
couple. (See Couple, Voltaic?) 

That element of a voltaic couple which is 
negative in the electrolyte of the cell. (See 
Electrolyte?) 

The negative plate of a voltaic cell is the plate 
not acted on by the electrolyte. In a zinc-carbon 



Pla.] 



407 



[Pla. 



couple in dilute sulphuric acid, the carbon plate 
is the negative plate. (See Cell, Voltaic.) 

The negative plate is to be carefully distin- 
guished from the negative pole, which is the ter- 
minal connected to the positive plate. The 
terminal connected to the negative plate is the 
positive pole. (See Cell, Voltaic.) 

Plate, Positive, of Storage Battery 

— That plate of a storage battery which is 
converted into, or covered by, a layer of lead 
peroxide, by the action of the charging current. 

That plate of a storage battery which is 
connected with the positive terminal of the 
charging source and which is, therefore, the 
positive pole of the battery on discharging. 

It will be noticed that the usage in this respect 
is the reverse of that in the case of primary bat- 
teries, in which the positive plate is positive in 
the liquid only; the end which projects from the 
liquid, or the terminal connected with it being 
negative. 

In storage batteries, the positive plate is con- 
nected with the positive pole. (See Battery, 
Storage. Cell, Voltaic.) 

Plate, Positive, of Yoltaic Cell 

The electro-positive element of a voltaic 
couple. (See Couple, Voltaic) 

That element of a voltaic couple which is 
positive in the electrolyte of the cell. (See 
Electrolysis?) 

The positive plate of a voltaic cell is the plate 
out from which the current flows through the 
electrolyte. 

The zinc plate of a zinc-carbon couple is the 
positive plate. (See Cell, Voltaic.) 

The current leaves the cell, however, to flow or 
pass through the external circuit at the wire or 
terminal connected with the negative plate. (See 
Cell, Voltaic.) 

Plate, Primary, of Condenser 

That plate of a condensing transformer in 
which the inducing charge is placed in order 
to induce a charge of different potential in the 
secondary plate. 

Plate, Secondary, of Condenser 

That plate of a condensing transformer in 
which the induced charge is produced by the 
induction of a charge on the primary plate. 
Plat3, Zinc, of Yoltaic Cell. Amalgama- 



tion of Covering the surface of the 

zinc plate of a voltaic cell with a thin layer of 
amalgam in order to avoid local action. (See 
Action, Local, of Voltaic Cell. Zinc, Amal- 
gamation of) 

Plates, Arrester A term sometimes 

applied to the two plates of an ordinary comb 
lightning arrester. (See Arrester, Lightning, 
Comb) 

The plate that is connected to the line to be 
protected, is more correctly called the arrester 
plate, and that connected to the ground the ground 
plate. 

Plates of Secondary or Storage Cell, 

Forming" of Obtaining a thick coating 

of lead peroxide on the lead plates of a storage 
battery, by repeatedly sending the charging 
current through the cell alternately in opposite 
directions. 

The effect of sending a current between two 
lead plates immersed in dilute sulphuric acid, is to 
coat one of the plates with lead peroxide. On the 
sending of the current in the opposite direction, 
the other plate is coated with lead peroxide. If 
now the current is sent in the opposite direction, 
more peroxide is deposited on one of the plates, 
and the peroxide at the other plate is converted 
into spongy lead. 

At the end of charging, the battery will form 
an independent source of current. (See Cell, 
Storage. ) 

Platform, Pole A platform, capable 

of supporting several men, placed on a termi- 
nal pole provided with a cable box, for the 
purpose of affording a ready means of inspect- 
ing and arranging the conductors in the box. 

Plating; Balance.— (S&eBalance, Plating) 

Plating; Bath, Electro (See Bath, 

Electro-Plating) 

Plating, Copper — Electro-plating 

with copper. (See Plating, Electro. Bath, 
Copper) 

Plating, Electro — The process of 

covering any electrically conducting surface 
with a metal by the aid of the electric 
current. 

By the aid of electro-plating, the baser metals 
are covered with silver, gold or platinum, or with 
any other metal, such as nickel or copper. 



Pla.] 



408 



[Pla. 



The process of electro-plating is carried on as 
follows: 

The object to be plated is connected with the 
negative terminal of a battery and placed in a so- 
lution of the metal with which it is to be plated, 
opposite a plate of that metal connected to the 
positive terminal of the battery. If, for example, 
the object is to be plated with copper, it is placed 
in a solution of copper sulphate or blue vitriol, 
opposite a plate of copper. By this arrangement 
the object to be plated forms the kathode of the 
plating bath, and the plate of copper forms the 
anode. 

On the passage of the current the copper sul- 
phate (Cu S0 4 ) is decomposed, metallic copper 
being deposited in an adherent layer on the arti- 
cles attached to the kathode, and the acid radical 
(S0 4 ) appearing at the anode, where it combines 
with one of the atoms of the copper plate. Since 
for every molecule of copper sulphate decomposed 
in the electrolyte, a new molecule of copper sulphate 
is thus formed, by the gradual solution of the copper 
anode, the strength of the solution in the bath is 
maintained as long as any of the copper plate re- 
mains at the anode, and the ordinary activity of 
the cell is not otherwise interfered with. 

When any other metals, such as gold, silver or 
nickel, for example, are to be deposited, suitable 
solutions of their salts are placed in the bath, and 
plates of the same metal hung at the anode. 

The character and coherence of the metallic 
coatings thus obtained depend on the nature and 
strength of the plating bath, and on the density 
of the current employed. The size and position 
of the anode, as compared with the size and posi- 
tion of the objects to be plated, must therefore be 
carefully attended to, as well as the strength of 




Fig. 43 Q. Electro- Plating 

the metallic solution and the current strength 
passing. (See Current Density.) 

Fig. 439, shows a bath arranged for silver- 
plating. 

The anode consists of a plate of silver. The 



spoons, forks, etc., to be plated are immersed in 
a suitable silver solution and connecied with the 
kathode. 

The electro-plating process when employed for 
the production of electrotype plates is called 
electrotyping. Here the object is to obtain a re- 
production in metal of any particular form, such 
as of type or of some natural object. It was 
called by Jacobi the galvanoplastic process. The 
term electrotyping is, however, more generally 
adopted. (See Electrotyping, or the Electrotype 
Process.) 

Plating, Gold Electro-plating with 

gold. (See Plating, Electro. Bath, Gold) 

Plating, Nickel Electro - plating 

with nickel. (See Plating, Electro. Bath r 

Nickel) 

Plating, Sectional Plating an article 

with a greater thickness of metal at certain 
points than at the rest of the surface. 

Sectional plating is employed for such objects 
as spoons, etc., which are, by this method, given 
a greater thickness of deposit at the under portions 
of the bowl and handle, where the spoon usually 
rests, and is, therefore, exposed to the greatest 
wear. 

Sectional plating is effected by means of sec- 
tional plating frames. (See Plating, Electro. 
Frames, Sectional Plating. ) 

Plating, Silver — Electro-plating 

with silver. (See Plating, Electro. Bath y 
Silver) 

Platinoid. — An alloy consisting of German 
silver containing i or 2 per cent, of metallic 
tungsten. 

Platinoid is suitable for use in resistance coils on 
account of the comparatively small influence pro- 
duced on its electric resistance by changes of 
temperature. 

Its resistance is 6o per cent, higher than that 
of German silver. 

Platinum. — A refractory and not readily 
oxidizable metal, of a tin-white color. 

The co-efficient of expansion of platinum by 
heat is very nearly that of ordinary glass. Pla- 
tinum is, therefore, generally employed for the 
leading-in conductors of an incandescent lamp. 
These conductors are fused into the glass of the 
lamp chamber. On the heating of the wires by 



Pla.] 



409 



[Plu. 



the current, the glass expands equally with the 
wires, and the vacuum in the lamp chamber is 
not, therefore, injured. 

Platinum Alloy. — (See Alloy, Platinum- 
Silver^) 

Platinum Black. — Finely divided platinum 
that possesses, in a marked degree, the power 
of absorbing or occluding gases. 

Platinum black is obtained by the action of 
potassium hydrate on platinum chloride. Unlike 
metallic platinum it is of a black color. 

Platinum Fuse. — (See Fuse, Platimwi.) 

Platinum-Silver Alloy.— (See Alloy, Plat- 
inum-Silver?) 

Platinum Standard Light.— (See Light, 
Platinum Standard.) 

Platymeter. — An instrument invented by 
Sir William Thomson for comparing the 
capacities of two condensers. 

Plow. — The sliding contacts connected to 
the motor of an electric street car, and placed 
within the slotted underground conduit, and 
provided for the purpose of taking off the 
current from the electric mains placed therein, 
as the contacts are pushed forward over them 
by the motion of the car. 

Similar contacts, placed in the rear of the motor 
car and drawn after the train, form what is techni- 
cally known as the sled, or when rolling on over- 
head wires as trolleys. (See Railroad, Electric.) 

Plow, Electric A plow driven by 

.an electric motor placed either on a wagon to 
which the plow is attached, or by a stationary 
electro-motor, by the aid of cords or other 
flexible belts. 

One of the first practical applications of the elec- 
tric transmission of energy was for the operation 
of a plow, driven electrically, by an electric current 
generated at some distance, and transmitted to 
the electric motor by suitable conductors. 

Plucker Tube.— (See Tube, Plucker) 

Plug. — A piece of metal in the shape of a 
plug, provided for making or breaking a cir- 
cuit by placing in, or removing from, a con- 
ical opening formed in the ends of two 
closely approached pieces of metal which are 



connected with the circuits to be made or 
broken. 

As the plug is inserted in the opening it bridges 
over the opening and thus closes the circuit con- 
nected with the separate pieces of metals. On 
removing the plug the circuit is opened or broken. 

Plug. — In telegraphy, an inexpert operator. 

Plug, Double A plug so constructed 

that when inserted in a spring-jack it makes 
two connections, one at its point and one at 
its shank. (See Spring-Jack.) 

Plug, Fusible A term sometimes 

applied to a safety fuse. (See Plug, Safety) 

Plug, Infinity A plug hole in a box 

of resistance coils, in which the two pieces of 
brass it connects are not connected by any 
resistance coil, and which, therefore, leaves, 
when withdrawn, an open circuit of an in- 
finite resistance. 



Plug, Safety 



-A wire, bar, plate or 



strip of readily fusible metal, capable of con- 
ducting, without fusing, the current ordinarily 
employed on the circuit, but which fuses, and 
thus breaks the circuit, on the passage of an 
abnormal current. (See Fuse, Safety.) 

A safety plug is only used on circuits in which 
the electro-receptive devices are connected with 
the leads in multiple. In this case the fusing of 
the safety plug, and the consequent opening of the 
circuit with which it is connected, does not affect 
the rest of the circuit. On series-connected circuits 
a different form of safety device is used. (See 
Cut -Out, Automatic, for Series -Connected Elec- 
tro-Receptive Devices. ) 

Plug, Short-Circuiting A plug by 

means of which one part of a circuit is cut 
out by being short-circuited. 

Plug Switch. — (See Switch, Plug) 

Plug, Wall A' plug provided for 

the insertion of a lamp or other electro-re- 
ceptive device in a wall socket, and thus con- 
necting it with a lead. 

Plugging. — Completing a circuit by means 
of plugs. 

Plugs, Grid Plugs of active ma- 
terial that fill the spaces or apertures in the 
lead grid or plate of a storage battery. 



Plu.] 



410 



[Pol. 



The active material forming the plugs is placed 
in the spaces in the grid while in the plastic con- 
dition. On the subsequent hardening of this ma- 
terial, these grid plugs cannot readily fall out, 
since the spaces are so shaped that their interior 
portions are of greater diameter than at the sur- 
face of the plates. 

Plumbago. — An allotropic modification of 
carbon. 

Plumbago, the material commonly known as 
black lead, is the same as graphite. Powdered 
plumbago is employed in electrotyping processes 
for rendering non-conducting surfaces electrically 
conducting. For this purpose powdered plum- 
bago is dusted on the surfaces, which thus acquire 
the power of receiving a metallic lustre by fric- 
tion. Stove polishes are formed of mixtures of 
plumbago and other cheap materials. (See 
Graphite.) 

Strictly speaking, the term graphite is properly 
applied to such varieties of plumbago as are suit- 
able for direct use for writing purposes, as in lead 
pencils. 

Plumbago, Coppered Powdered 

plumbago coated with copper, for use in the 
metallization of objects to be electro-plated. 
(See Metallization) 

Plumbago, Gilt Powdered plum- 
bago whose conducting power* for electricity 
has been increased by coating it with metallic 
gold. 

Gilt plumbago is used for rendering non-con- 
ducting surfaces electrically conducting and thus 
preparing them for electro-plating. 

To prepare gilt plumbago, dissolve in ioo parts 
of sulphuric ether I part of chloride of gold, mix 
in this 60 parts of powdered plumbago, and ex- 
pose to air and light until all ether has volatilized. 
Then dry in an oven. 

Plumbago, Silvered Powdered 

plumbago coated with metallic silver for use 
in the metallization of objects to be electro- 
plated. 

Plunge Battery. — (See Battery, Plunge) 

Pneumatic Perforator. — (See Perforator, 
Pneumatic) 

Pneumatic Signals, Electro (See 

Signals, Electro-Pneumatic.) 

Pockets, Armature Spaces pro- 



armature coils. (See Coils, Armature, of 
Dynamo-Electric Machine) 

PoggendorfTs Voltaic Cell.— (See Cell, 
Voltaic, Pog-gendorff's) 

Point, Carbon A term formerly 

applied to the carbon electrodes used in the 
production of the voltaic arc. 

Point, Indifferent A point in the 

intra-polar regions of a nerve where the ane- 
lectrotonic and kathelectrotonic regions meet, 
and where the excitability is therefore un- 
changed. 

This is sometimes called the neutral point. 

Point of Lightning Rod. — (See Pod, 
Lightning, Points on) 

Point of Origin. — (See Origin, Point of) 

Point, Neutral In electro-thera- 
peutics, a term sometimes used instead of in- 
different point. (See Point, Indifferent) 

Point, Nodal — The null point in a 

circuit traversed by electric oscillations. (See 
Point, Null) 

Point, Null : Such a point on a 

micrometer circuit, that when joined or con- 
nected with the second- 
ary circuit of an in- 
duction coil, the sparks 
in the micrometer cir- 
cuit are either very 
greatly decreased or 
are entirely absent. 

The null point on the 
micrometer circuit is situ- 
ated symmetrically with 
respect to the micrometer 
knobs. 

If the induction coil A, 
Fig. 440, has its second- 
ary circuit connected as 
shown with the microm- 
eter circuit at the point e, situated at the centre 
of the micrometer circuit, the point will be a null 
point, and the effects of sparks at the micrometer 
knobs, at M, will be greatly decreased. Under 
the conditions shown in the figure, the electrical 
oscillations in the micrometer circuit must be re- 
garded as in the condition of stationary waves or 
vibrations. It would seem, therefore, that defi- 




Fig. 440. Null Point. 



vided in an armature for the reception of the nite waves or vibrations are setup in themicrom- 



Poi.] 



411 



[Pol. 



eter circuit, in the same way as are the vibra- 
tions produced in an elastic bar set in vibration 
by a violin bow, or by a blow from a hammer. 

Points, Consequent The points or 

places in an anomalous magnet where the 
consequent poles are situated. (See Magnet, 
Anomalous. Pole, Anomalous.) 

Points, Corresponding — Points 

where the lines of electrostatic force sur- 
rounding an insulated charged conductor 
enter the surfaces of neighboring conductors. 

Points on the surface of a body placed in 
an electrostatic field where the lines of elec- 
trostatic force enter its surface, and thus pro- 
duce a charge equal and opposite to that 
of the surface of the body at the points from 
which they came. 

Corresponding points receive, in accordance 
with the laws of electrostatic induction, charges 
equal and opposite to those of the surfaces from 
which the lines of electrostatic force originate. 

Points, Electric Action of The 

effect of points placed on an insulated, 
charged conductor, in slowly discharging the 
conductor by electric convection. (See Con- 
vection, Electric.) 

The cause of this action of points is to be at- 
tributed to the increased density of a charge on 
the surface of a conductor at the points and the 
consequent production of convection streams of 
air, which thus gradually carry off the charge. 
(See Charge, Distribution of.) 

Points, Iso-Electric A term some- 
times used in electro-therapeutics for points 
of equal potential. 

Points, Neutral, of Dynamo-Electric Ma- 
chine Two points of greatest differ- 
ence of potential, situated on the commutator 
cylinder, at the opposite ends of a diameter 
thereof, at which the collecting brushes must 
rest in order to carry off the current quietly. 

These are called the neutral points because the 
coils that are short-circuited by the brushes lie in 
the magnetically neutral points of the armature. 
(See Line, Neutral, of Commutator Cylinder.) 



Points, Neutral, of Magnet Points 

approximately midway between the poles of 



a magnet. (See Line, Neutral, of a Magnet. 
Magnet, Equator of.) 

Points, Neutral, of Thermo-Electric Dia- 
gram The points on a thermo-electric 

diagram where the lines representing the 
thermo-electric powers of any two metals 
cross one another. 

A mean temperature for any two metals in 
a thermo-electric series, at which, if their two 
junctions are slightly over and slightly under 
the mean temperature (the one as much 
above as the other is below), no effective 
electromotive force is developed. (See Dia- 
gram, Thermo-Electric . Couple, Thermo- 
Electric^) 

Points or Rhumbs of Compass.— (See 
Compass, Points of.) 

Polar Region. — (See Region, Polar.) 

Polar Tips.— (See Tips, Polar.) 

Polarity, Diamagnetic A polar- 
ity the reverse of ordinary magnetic polarity, 
the existence of which was assumed by Fara- 
day to explain the phenomena of diamag- 
netism. (See Diamagnetism.) 

Faraday assumed that diamagnetic substances, 
when brought into a magnetic field, acquired 
north magnetism in those parts that were nearest 
the north pole, instead of south mag7ietism, as. 
with ordinary magnetic substances. The north 
pole thus obtained would, he thought, explain 
the apparent repulsion of a slender rod of any di- 
amagnetic material delicately suspended in a 
strong magnetic field, and cause it to point equa- 
torially, or with the lines of force passing through 
its least dimensions. This supposition was subse- 
quently abandoned by Faraday. It has recently 
been revived by Tyndall. (See Diamagnetism.)- 

The action of a diamagnetic body, when placed 
in a magnetic field, is now generally ascribed to 
the fact that the atmosphere, by which such body 
is surrounded, is more powerfully paramagnetic 
than the diamagnetic substance. The diamag- 
netic substance comes to rest in an equatorial posi- 
tion, because in that position there is the greatest 
length of air in the path of the magnetic lines, 
which has a smaller magnetic resistance than the 
diamagnetic substance. 

Polarity, Magnetic The polarity 

acquired by a magnetizable substance when 
brought into a magnetic field. 



Pol.] 



412 



[Pol. 



The direction of magnetic polarity, acquired by 
a substance when brought into a magnetic field, 
depends on the direction in which the lines of 
magnetic force pass through it. Where these 
lines enter the substance a sou h pole is pro- 
duced, and where they pass out, a north pole is 
produced. The axis of magnetization lies in the 
direction of the lines of force as they pass 
through the body, and the intensity of magnetiza- 
tion depends on the number of these lines of 
force which pass through the body. 

The cause of magnetic polarity is not definitely 
known. Hughes' hypothesis attributes it to a 
property inherent in all matter. Ampere at- 
tributes it to closed electric circuits in the ultimate 
particles. Whatever its cause, it is invariably 
manifested by a magnetic field, the lines of force of 
which are assumed to have the direction already 
mentioned. (See Magnetism, Hughes' 1 Theory 
of. Magnetism, Ampere' 's Theory of Magnet- 
ism, Ewing" 1 s Theory of.) 

Polarization, Galvanic A term 

sometimes applied to the polarization of a 
voltaic cell. (See Cell, Voltaic, Polariza- 
tion of.) 

Polarization, Internal, of Moist Bodies 

A polarization exhibited by such 

moist bodies as the nerves, muscular fibres, 
the juicy parts of vegetables and animals, or 
in general by all bodies possessing a firm struc- 
ture filled with a liquid, on the passage 
through them of a strong electric current. 

Polarization, Magnetic Rotary 

The rotation of the plane of polarization of a 
beam of plane-polarized light consequent on 
its passage through a plate of glass subjected 
to the stress of a magnetic field. (See Rota- 
tion, Magneto-Optic?) 

Polarization of Dielectric. — (See Dielec- 
tric, Polarization of.) 

Polarization of Electrolyte. — (See Elec- 
trolyte, Polarization of.) 

Polarization of Voltaic Cell. — (See Cell, 
Voltaic, Polarization of.) 

Polarized Armature. — (See Ar?nature, 
Polarized.) 

Polarized Relay. — (See Relay, Polarized.) 

Polarizing Current. — (See Current , 
Polarization,) 



Polarizing Electro-Therapeutic Current. 

— (See Current, Electro- Therapeutic Polar- 
izing?) 

Pole, Analogous That pole of a 

pyro-electric substance, like tourmaline, which 
acquires a positive electrification while the 
temperature of the crystal is rising. (See 
Electricity, Pyro.) 

Pole, Anomalous A name some- 
times given to those parts or poles in an 
anomalous magnet which consist of two simi- 
lar free poles placed together. (See Magnet, 
Anomalous.) 

Pole, Antilogous That pole of a 

pyro-electric substance, like tourmaline, which 
acquires a negative electrification when the 
temperature of the crystal is rising, and a 
positive electrification when it is falling. (See 
Electricity, Pyro.) 

Pole, Armature (See Armature, 

Pole?) 

Pole Changer. — A switch or key for chang- 
ing or reversing the direction of current pro- 
duced by any electric source, such as a bat- 
tery 

The commutator of a Ruhmkorff coil is a sim- 
ple form of pole changer. It is, however, usu- 
ally called a commutator. (See Coil, Induction. ) 

Pole-Changing and Interrupting Elec- 
trode Handle. — (See Electrode-Handle, . 
Pole-Changing and Interrupting?) 

Pole-Changing Switch. — (See Switch, 
Pole- Changing.) 

Pole Climbers. — (See Climbers, Pole?) 

Pole, Consequent A magnet pole 

formed by two free north or two free south 
poles placed together. (See Magnet, Ano?n- 
alous.) 

Pole, Magnetic, Austral A name 

formerly employed in France for the north- 
seeking pole of a magnet. 

That pole of a magnet which points to the 
earth's geographical north. 

It will be observed that the French regarded the 
magnetism of the earth's Northern Hemisphere 



Pol.] 



413 



[Pol. 



as north, and so named the north-seeking pole of 
the needle the austral or south pole. 

The north-seeking pole of the magnet is some- 
times called the boreal or north pole. (See Pole, 
Magnetic, Boreal.) 

Pole, Magnetic, Boreal A name 

formerly employed in France for the south- 
seeking pole of a magnet, as distinguished 
from the austral or north-seeking pole. 

That pole of a magnet which points to- 
ward the geographical south. 

If the earth's magnetic pole in the Northern 
Hemisphere be of north magnetism, then the pole 
of a needle that points to it must be of the oppo- 
site polarity, or of south magnetism. In this 
country we call the end which points to the north, 
the north-seeking pole or marked pole. In 
France the end which points to the north was 
formerly called the austral pole. Austral means 
south pole. (See Pole, Magnetic, Austral.) 

Pole, Magnetic, False A term pro- 
posed by Mascart and Joubert to designate 
the place or places on the earth which appar- 
ently act as magnetic poles, in addition to 
the two true magnetic poles, near the earth's 
geographical poles. 

According to these authorities, the earth pos- 
sesses two magnetic poles only, viz., a negative 
pole in the Northern Hemisphere and a positive 
pole In the Southern Hemisphere. The addi- 
tional poles are called by them the false magnetic 
poles. 

Pole, Magnetic, Free A pole in a 

piece of iron, or other paramagnetic sub- 
stance, which acts as if it existed as one mag- 
netic pole only. 

A free magnetic pole has in reality no physical 
existence. The conception, however, is of use in 
describing certain magnetic phenomena. If the 
bar of iron be so long as to practically place one 
pole beyond the sensible action of the other, either 
pole may be regarded as a free pole. 

Pole, Magnetic, Marked That pole 

of a magnetic needle which points approxi- 
mately to the earth's geographical north. 
(Obsolete.) 

The north-seeking pole of a magnetic needle. 

Pole, Magnetic, North That pole 

of a magnetic needle which points approxi- 
mately to the earth's geographical north. 



The north-seeking pole of a magnetic 
needle. 
Pole, Magnetic, North-Seeking 

That pole of a magnetic needle which points 
approximately towards the earth's geographi- 
cal north. 

Pole, Magnetic, Salient — A term 

sometimes applied to the single poles at the ex- 
tremities of an anomalous magnet, in order to 
distinguish them from the double or consequent 
pole formed by the juxtaposition of two simi- 
lar magnetic poles. (See Magnet, Anoma- 
lous^) 

Pole, Magnetic, South That pole 

of a magnetic needle which points approxi- 
mately towards the earth's geographical south. 

The south-seeking pole of a magnetic 
needle. 

Pole, Magnetic, South-Seeking 

That pole of a magnetic needle which points 
approximately toward the geographical south. 

Pole, Negative That pole of an 

electric source through which the current is 
assumed to enter or flow back into the source 
after having passed through the circuit ex- 
ternal to the source. 

Pole-Pieces of Dynamo-Electric Machine. 

— (See Pieces, Pole, of Dynamo-Electric 
Machine?) 

Pole Platform.— (See Platform, Pole.) 



-That pole of an 



Pole, Positive — 

electric source out of which the electric cur- 
rent is assumed to flow. 

Pole Steps. — Short rods or bars shaped so 
as to be readily inserted in holes near the 
base of telegraph or electric light poles, so as 
to serve as steps to enable a lineman to reach 
the permanently placed steps. 

Permanent steps are placed only at some dis- 
tance from the ground, in order to prevent the 
ready climbing of the poles by unauthorized 
persons. 

Pole, Telegraphic A wooden or iron 

upright on which telegraphic or other wires 
are hung. 

Wooden poles are generally round. 



Pol.] 



414 



[Pol. 



The terminal pole, or the last pole at each end 
of the line, or where the wires bend at an angle 
of nearly 90 degrees, is made larger than usual 
and is often cut square. 

The holes for the poles must be dug in the true 
line of the wires, and not at an angle to such line. 
As little ground should be disturbed in the dig- 
ging as possible. Earth borers, or modifications 
of the ordinary ship auger, are generally em- 
ployed for this purpose. When the pole is placed 
in position the ground should be rammed or 
punned around the pole. 

In setting the pole, it is generally buried at least 
5 feet in the ground. In England the poles are 
planted to a depth of about one- fifth of their 
length. In embankments and loose ground, they 
are planted deeper than in more solid earth. On 
curves, the poles should be inclined a little so as 
to lean back against the lateral strain of the wire, 
since by the time the ground has completely set, 
the strain of the wire will have pulled them into 
an erect position. 

Care must be taken to so plant the poles on 
that side of a road or railway that the prevailing 
winds will blow them off the roadbed, should it 
overturn them. As to location, the top of steep 
cuttings is preferable to the slope. In all exposed 
positions, it is preferable to strengthen the poles 
by stays attached to both sides. 

Where the number of wires is unusually large, 
heavy timber, or in case of its absence, double 





Fig. 441. Telegraphic 
Brackets. 



Fig. 442. Telegraphic 
Arms. 



poles suitably braced together, must be employed. 
In long lines the poles should all be numbered in 
order to afford ease of reference in case of repair. 

When, even with the best punning, and other 
precautions, the pole is judged to be unable to 
resist the strain on it, stays and struts are em- 
ployed. A stay is used when it is desired to re- 
move the pull or tension from the pole ; a strut, 
when it is desired to remove the thrust ox pressure. 

The arms or brackets, or the cross-pieces that 



support the insulators, should all be placed orx 
the same side of the poles. Some common forms- 
of brackets are shown in Fig. 441, and of tele- 
graphic arms in Fig. 442. 

Saddle brackets should be placed on alternate 
sides of the poles. When the strain on an insula- 
tor is too great, on account of the wire going off 
at a sharp angle, a shackle is used. This is a 
special form of insulator which confines the strain, 
to one spot. 




Fig. 443. Double Shackles. 

A form of double shackle is shown in Fig. 
443. The wire passes around the recess at B r 
between the two insulators. 

On curves, or in any situation where there is a 
probability, in case of the breaking of an insula- 




Fig. 444. Hook Guard. 

tor, of a wire getting into a dangerous position, 
guards should be employed. 

Guards are of two kinds, viz.: hoop guards 
and hook guards. A form of hook guard is- 
shown in Fig. 444. 

When wooden poles are employed various pre- 
servative methods are adopted to protect the- 
wood from decay, which is very apt to occur, 
especially where the pole enters the ground. 
Some of these forms are as follows, viz. : 

(1.) Charring and tarring the butt end of the 
pole where it enters the ground, so as to expel 
the sap and destroy injurious plant or animal 
germs. 



Pol. 



415 



[Por, 



The charred end is then cleansed and dipped 
in a mixture of tar and slaked lime. 

(2.) Burnetizing, or the introduction of 
chloride of zinc into the pores of the wood, by 
placing the poles in an open tank filled with a 
solution of this salt. 

(3.) Kyanizing, or the similar introduction of 
corrosive sublimate, or mercuric chloride. 

(4.) Boucher izing, or the injection of a solution 
of copper sulphate into the pores of the wood. 

(5.) Creosoting, or the application of creosote 
to well seasoned poles. 

Pole, Telegraphic, Punning of 

Ramming or packing the earth around the 
base of a telegraph pole for the purpose of 
more securely fixing it in the ground. 

Pole, Telegraphic, Terminal The 

pole at either end of a telegraphic line. 

As the first or last pole in a telegraphic line is 
not supported on opposite sides by the line wires, 
it is generally made stouter than the intermediate 
poles, and greater care is taken to fix it securely 
in the ground. 

Pole, Testing A term sometimes 

employed in electro-therapeutics for the in- 
different pole or electrode. (See Electrode, 
Indifferent?) 

Pole, Trolley The pole which sup- 
ports the trolley bearing and rests on the 
socket in the trolley base frame in an over- 
head wire electric railway system. 

Pole, Unit, Magnetic A magnetic 

pole of such a strength that it would act with 
a unit or dyne of force on another unit pole at 
a distance of one centimetre. 

— The name given 



Poles, Consequent — 

to single magnetic poles formed by two free 
N. poles or two free S. poles placed together. 
(See Magnet, Anomalous}) 

Poles, Idle Poles or electrodes in 

Crookes' tubes, between which discharges are 
not taking place. 

The idle poles have no connection with the in- 
duction coils or other sources from which the elec- 
tric discharges are obtain- d. These poles are pro- 
vided for attaching galvanometer wires, etc., in the 
study of the Edison effect, or for the etudy of the 



electrical condition of the dark space and other 
regions of the atmosphere of the tube. 

Poles, Magnetic The two points 

where the lines of magnetic force pass from 
the iron into the air, and from the air into 
the iron. 

The two points in a magnet where the 
magnetic force appears to be concentrated. 

In reality the magnetic force is most concen- 
trated at the neutral points of a m agnet, through 
which all the lines of force pass. 

All magnets possess at least two poles, one 
positive or north, and the other negative or south. 

The lines of magnetic force are assumed to 
come out of a magnet at its north pole, and to 
enter it at its south pole. 

Poles, Magnetic, of Yerticity (See 

Verticity, Poles of, Magnetic?) 

Poles of Condenser. — The terminals of a 
condenser. (See Condenser.) 

Poles of Magnetic Intensity. — (See In- 
tensity, Magnetic, Pole of.) 

Polyphase Current. — (See Current, 
Multi-Phase?) 

Polyphotal Arc Light Regulators. — (See 
Regulator, Polyphotal Arc-Light?) 

Popgun, Electro-Magnetic A mag- 
netizing coil, provided with a tubular space 
for the insertion of a core, much shorter than 
the length of the coil, which, when the ener- 
gizing current is passed through the coil, 
is thrown violently out from the coil. 

The movement and consequent expulsion of the 
core is due to the action of the lines of magnetic 
force which complete their circuit through the 
core. 

Porcelain. — A variety of insulating ma- 
terial. 

A translucent variety of earthenware. 
Porous Cell. — (See Cell, Porous?) 
Porous Cup. — (See Cup, Porous?) 
Porous Insulation. — (See Insulation, 
Porous.) 

Porous Jar. — (See far, Porous.) 
Porret's Phenomena. — (See Pheno?nena, 
Porret.) 



PorJ 



416 



fPos. 



Portative Power. — (See Power, Porta- 
tive^) 

Portelectric. — An electric carrier. 

A system of electric transportation by- 
means of the successive attractions of a num- 
ber of hollow helices of insulated wire on a 
hollow solenoidal iron car. 

The solenoidal car forms the movable core of the 
helical coils. As it moves through these coils it 
automatically closes the circuit of an electric cur- 
rent through the coils in advance of it and opens 
the circuit of the coils in its rear. In this way the 
solenoidal car advances in a line coincident with 
the axis of the helical coils, being virtually sucked 
through them by their magnetic attractions. This 
system of electric propulsion is unique in systems 
of electric traction. The motor becomes a mere 
mass of iron or other paramagnetic material. 
The system is suitable for the carriage of mail or 
other comparatively light articles at a high speed. 

In an experimental plant at Dorchester, Mass., 
a track of 2,784 feet in length was laid in the ap- 
proximate form of an oval. The track was 
formed by an upper and lower rail of steel, suit- 
ably supported by stringers. 

The car, which forms the movable core of the 
solenoidal coils, was of wrought iron, and was 
cylindrical in shape, with conical ends. It was 



placed on the top of the carrier and connected the 
several helices successively with the electric 




Fig. 445. Portelectric Track. 

12 feet in length and 10 inches in diameter, and 
weighed about 500 pounds. It would carry about 
10,000 letters. It had two flanged wheels above 
and two below. 

The solenoidal coils, by the attractive power of 
which the core was moved, embraced the track 
and the movable core or carrier. They were 
fixed along the track at intervals of 6 feet from 
centre to centre. Each coil was formed of 630 
turns of No. 14 copper wire. The upper track 
rail is divided into sections which form conductors 
for the driving current. A central wheel was 




Fig. 446. Portelectric Car. 
source as the carrier was drawn forward. A 
speed of about 34 miles an hour was reached. 

A section of the track is shown in Fig. 445, and 
the shape and general structure of the carrier in 
Fig. 446. 

Portrait, Electric A portrait 

formed on paper by the electric volatilization 
of gold or other metal. 

An electric portrait is obtained by cutting on 
a thin card a portrait in the form of a stencil. A 
sheet of gold leaf is then placed on one side of the 




Fig. 447. Electric Portrait. 

paper stencil, and a sheet of paper on the other 
side ; sheets of tin-foil are then placed on the out- 
side, as shown in Fig. 447, and the whole firmly 
pressed together. If, now, a disruptive discharge 
is passed through from one sheet of tin-foil to the 
other, the gold leaf is volatilized, and a purplish 
stain is left on the paper of the outlines of the 
stenciled card, thus forming an electric portrait. 

Position, Energy of A term used 

for stored energy, or potential energy. (See 
Energy, Potential^) 

Positive Direction of a Simple-Harmonic 
Motion. — (See Motion, Simple-Harmonic, 
Positive Direction of.) 



Pos.] 



417 



[Pot. 



Positive Direction of Lines of Magnetic 
Force. — (See Force, Magnetic, Lines of, 
Positive Direction of.) 

Positive Direction of the Electrical Con- 
vection of Heat.— (See Direction, Positive, 
of Electrical Cojivection of Heat.) 

Positive Direction Round a Circuit. 
— (See Directioii, Positive, Round a Cir- 
cuity 

Positive Direction Through a Circuit. 
— (See Direction, Positive, Through a Cir- 
cuity 

Positive Electricity. — (See Electricity, 
Positive) 

Positive Electrode. — (See Electrode, 
Positive?) 

Positive Feeders. — (See Feeders, Posi- 
tive) 

Positive-Onmibus Bars. — (See Bars, Posi- 
tive Omnibus) 

Positive Phase of Electrotonns. — (See 
Electrotonus, Positive Phase of) 

Positive Plate of Storage Battery. — (See 
Plate, Positive, of Storage Battery) 

Positive Plate of Toltaic Cell.— (See 
Plate, Positive, of Voltaic Cell) 

Positive Pole. — (See Pole, Positive) 

Positive Potential. — (See Potential, Posi- 
tive) 

Positive Side of Circuit. — (See Circuit, 
Positive Side of) 

Positively.— In a positive manner. 

Positively Excited. — Excited or charged 
with positive electricity. (See Electricity, 
Positive) 

Post, Binding" A device for con- 
necting the terminal of an electric source 
with the terminal of an electro-receptive de- 
vice, or for connecting different parts of an 
electric apparatus with one another. 

The conducting or circuit wire is either intro- 
duced in the opening a, or c', Fig. 448, and 
clamped by the screw b, or b', or is placed in 
the space d, d, and kept in place by means of a 
thumbscrew. Sometimes two openings are 
provided at c, and c', for the purpose of connect- 
ing two wires together. 



A device for coupling or connecting the ends 
of two wires to each other. It is then called a 
coupler. (See Couple, Voltaic.) 

V 




Fig. 448. Binding Posts. 

Pot, Porous The porous jar or cell 

of a voltaic cell. (See Cell, Porous) 

Potential, Alternating A poten- 
tial, the sign or direction of which is alter- 
nately changing from positive to negative. 

An alternating potential may be obtained either 
in the case of an electrostatic field, or in that 
of a magnetic field. 

Potential, Alternating Electrostatic 

— The potential of a charge that is under- 
going rapid alternations. 
Potential, Alternating, Magnetic 

The difference of magnetic potential pro- 
duced by alternating electric currents. 

Potential, Constant A potential 

which remains constant under all conditions. 

A machine or other electric source is said to 
have a constant potential when it is capable, 
while in operation, of maintaining a constant 
difference of electric pressure between its two 
terminals on changes of load. (See Circuit, 
Constant -Potential. ) 

Potential, Difference of ■ — A term 

employed to denote that portion of the 
electromotive force which exists between 
any two points in a circuit. 

The difference of potential at the poles of any 
electric source, such as a battery or dynamo, is 
that portion of the total electromotive force 
which is available, and is equal to the total 
electromotive force, less what is lost in the 
source. 

Some difference of opinion exists as to the exact 
meaning that is attached to the phrase difference 
of potential. 

A positively electrified body is said to have a 
higher electric potential than the earth, whose 
potential is taken as zero. 



Pot.] 



418 



TPot 



Potential, Difference of, Methods of 
Measuring Methods employed for de- 
termining differences of potential. 

These methods are as follows: 

(i.) By the Method of Weighing, that is, by 
obtaining the weight required to overcome the 
attraction between two oppositely charged plates, 
or oppositely energized coils; or by measuring 
the repulsion between similarly charged surfaces, 
or similarly energized coils. 

(2.) By the Use of Electrometers, or apparatus 
designed for measuring differences of potential. 
(See Electrometers. ) 

(3.) By the Use of Galvanometers. 

Differences of potential, in the case of currents, 
may be determined from the quantity of electri- 
city which flows per second through a given 
circuit, that is, by the number of amperes, just 
as the pressure of water at any point in the side 
of a containing vessel can be determined by the 
quantity of water that flows per second. Differ- 
ence of potential in the case of currents, there- 
fore, may be measured by any galvanometer 
which measures the current directly in amperes, 
provided the resistance of the circuit is known. 

Potential, Drop of A term some- 
times used instead of fall of potential. (See 
Potential, Fall of) 

Potential, Electric The power of 

doing electric work. 

Electric level. 

Electric potential can be best understood by 
comparison with the case of a liquid such as 
water. 

The ability of a water supply or source to do 
work depends: 

(1.) On the quantity of water. 

(2. ) On the level of the water, as compared with 
some other level; or, in other words, on the dif- 
ference between the two levels. 

In a like manner the ability of electricity to do 
work depends: 

(1.) On the quantity of electricity. 

(2.) On the electric potential at the place where 
the electricity is produced, as compared with that 
at some other place; or, in other words, on the 
difference of potential. 

In the case of water flowing through a pipe, 
when its flow has been fully established, the quan- 
tity which passes in a given time is the same at 
any cross-section of the pipe. 



In the case of electricity, the quantity of elec- 
tricity flowing through any conductor, or part of 
a circuit, is the same at any cross- secdon. A gal- 
vanometer introduced into a break in any part of 
the conductor would show the same strength of 
current. 

But, though the quantity of water which passes 
is the same at any cross-section of a pipe, the 
pressure per square inch is not the same, even in 
the case of a horizontal pipe of the same diameter 
throughout, but becomes less, or suffers a loss of 
head, or difference of pressure, at any two points 
along the pipe. This difference of pressure causes 
the flow of water between these two points against 
the resistance of the pipe. 

So, too, in the case of a conductor carrying an 
electric current, when the full current strength 
has been established, the quantity of electricity 
that passes is the same at all cross-sections. 



■-■ g' 



Fig. 44Q . Hydraulic Gradient. 

The electric pressure or potential, however, 
is by no means the same at all points in the 
conductor, but suffers a loss of electric head or 
level, in the direction in which the electricity is 
flowing. It is this electric head or level, or dif- 
ference of electric potential, that causes the elec- 
tricity to flow against the resistance of the con- 
ductor. 

These analogies can be best shown by the fol- 
lowing illustration: 

In Fig. 449, a reservoir, or source of water, at 
C, communicates with the horizontal pipe A B, 
furnished with open vertical tubes at a, b, c, d, e, 
f, g, and B. If the outlet at B, is closed, the level 
of the water in the communicating vessels is the 
same as at the source; but if the liquid escape 
freely from B, the level of the water in the branch 
pipes will be found on the inclined dotted line, or 
at a', b', c', d', e', f, g', which may be called 
the hydraulic gradient. 

The pressure per square inch, at any cross sec 
tion of the horizontal pipe, which is measured by 
the height of the liquid in the vertical pipe at that 
point, decreases in the direction in which the liquid 
is flowing. The force that urges the liquid 



Pot.] 



419 



rpot. 



through the pipe between any two points, may 
be called the liquid-motive force {Fleming) and is 
measured by the difference of pressure between 
these points. " 

In Fig. 450, the dynamo-electric machine at D, 
has its negative pole grounded, and its positive 
pole connected to a long lead, A B, the positive 
pole of which is also grounded. A fall of poten- 
tial, represented by the inclined dotted line, 
occurs between A and B, in the direction in which 
the electricity is flowing. 



[ YT 



r-f 



rt^ 



— ^ 



Fig. 450. Fall of Electric Potential. 

The dynamo-electric machine may be regarded 
as a pump that is raising the electricity from a 
lower to a higher level, and passing it through 
the lead A B. The electric pressure or potential 
producing the flow is greatest near the dynamo and 
least at the further end, the differences at the 
points a, b, c, d, e, f, and g, being represented by 
the vertical lines a a', bb', cc', dd'.ee', ff, and 

gg'. 

The electricity flows between any two points as 
a and b, in the conductor A B, in virtue of the 
difference of electric pressure or potential be- 
tween these two parts, or the difference between 
a a' and b b'. 

Differences of potential must be distinguished 
from differences in electric charge, or electrostatic 
density. If two conductors at different potentials 
are connected by a conductor, a current will flow 
through this conductor. When their potential is 
the same, no current flows. The density of a 
charge is the quantity of electricity per unit of 
area. 

The electric potential is the same at all points 
of an insulated charged conductor ; the density is 
different at different points, except in the case of 
a sphere. The potential, however, is the same, 
since no current flows, or the charge does not re- 
distribute itself. The density on an insulated, 
isolated sphere, is uniform over all parts of the 
surface, and its potential is the same at all points, 
tlf now the sphere be approached to another body, 
its density will vary at different parts of its sur- 



face, and while the charge is redistributing itself 
so as to produce these differences in density the 
potential will vary. As soon, however, as this 
redistribution is effected and no further current 
exists, the potential is the same over all points, 
though the density differs at different points. 

An electric source not only produces but also 
maintains a difference of potential. In the case 
of the flow of liquid in a pipe, if a continuous 
current of the liquid be maintained from the 
higher level in the reservoir to a lower level, as, 
for example, by means of a pump, it must flow 
through the pump to the reservoir, from the lower 
level towards the higher level. In case of an 
electric source, since the thing called electricity 
flows through a closed circuit, if its direction of 
flow in that part of the circuit extern A to the 
source — i. e. , in the external or useful current — ■ 
be from a higher to a lower level, then its flow 
through the remainder of the circuit — i. e., 
through the source — must be from the lower to the 
higher level. Since, however, the electrical po- 
tential of a body represents the work the elec- 
tricity is capable of doing, the work done by the 
e'ectricity may be regarded as being that done 
when it passes from the higher to the lower level. 

Potential, Electrostatic — The 

power of doing work possessed by a unit 
quantity of positive electricity charged or re- 
siding on an insulated body. 

Potential, Electrostatic, Difference of 

Difference of potential of an electric 

charge. (See Potential, Difference of. 
Electrostatics?) 

Potential Energy.— (See Energy, Poten- 
tial^ 

Potential, Fall of A decrease of 

potential in the direction in which an elec- 
tric current is flowing, proportional to the re- 
sistance when the current is constant. (See 
Potential, Electric?) 

Potential Galvanometer. — (See Galva- 
nometer, Potential.) 

Potential Indicator.— (See Indicator, 
Potential?) 

Potential, Magnetic The amount 

of work required to bring up a unit north- 
seeking magnetic pole from an infinite dis- 
tance to a given point in a magnetic field. 



Pot.] 



420 



[Pow. 



Potential of Conductor, Methods of 

Varying (See Conductor, Potential 

of, Methods of Varying) 

Potential of Conductors. — (See Conduc- 
tor, Potential of.) 

Potential, Negative That potential 

in the circuit external to the source towards 
which the electric current flows. 

Generally the lower potential, or lower 
level. 

Potential, Positive That potential 

in the circuit external to the source, from 
which the electric current flows. 

The higher potential or higher level. 

Potential, Uniform — A potential 

that does not vary. 

A constant potential. (See Potential, Con- 
stant^) 

An electric source is said to generate a uniform 
potential when it maintains a constant difference 
of potential at its terminals. 

Potential, Unit Difference of 

Such a difference of potential between two 
points that requires the expenditure of one 
erg of work to bring a unit of positive elec- 
tricity from one of these points to the other, 
against the electric force. (See Erg) 

The practical unit of difference of potential is 
the volt. (See Volt.) 

Potential, Zero An arbitrary level 

from which electric potentials are measured. 

As we measure the heights of mountains from 
the arbitrary mean level of the sea, so we measure 
electric levels from the arbitrary level of the po- 
tential of the earth. 

Potentiometer. — An apparatus for the 
galvanometric measurement of electromotive 
forces, or differences of potential, by a zero 
method. (See Method, Null or Zero.) 

In the potentiometer the difference of potential 
to be measured is balanced or opposed by a 
known difference of potential, and the equality 
of the balance is determined by the failure of one 
or more galvanometers, placed in shunt circuits, 
to show any movement of their needles. 

The principle of operation of the potentiometer 
will be understood from an inspection of Fig. 451. 
A secondary battery S, has its terminals con- 



nected to the ends of a uniform wire A B, of high 
resistance called the potentiometer wire. There 
will, therefore, occur a regular drop or fall of po- 
f tential along this wire, which, since the wire is 
uniform, will be equal per unit of length. This 
drop of potential can be shown by connecting the 
terminals of a delicate galvanometer, generally of 
high resistance, to different parts of the wire, 
when the deflection of the needle will be propor- 

S 




Fig. 4JZ. Potentiometer. 

tional to the drop of potential between the two' 
points of the wire touched. If, now, the terminals 
of a standard cell be inserted in the circuit of 
the galvanometer, so as to oppose the current 
taken from the potentiometer wire, and the con- 
tacts of the potentiometer wire be slid along the 
wire until no deflection of the galvanometer needle 
is produced, the drop of potential between these 
two points on the wire will be equal to the differ- 
ence of potential of the standard cell. (See Cell, 
Voltaic, Standard. ) 

Suppose, now, it be desired to measure the dif- 
ference of potential between two points a and b, 
on the wire C, through which a current is flow- 
ing. Connect the points b and d, and a and c, 
as shown, with the delicate high resistance gal- 
vanometer G, in either of them. Now slide c, 
towards d, until the needle of G, shows no deflec- 
tion. The potential between a and b, is then 
equal to that between c and d. 

Potentiometer Wire. — (See Wire, Po- 
tentiometer.) 

Power. — Rate of doing work. 

Mechanical power is generally measured in 
horse power, which is equal to work done at the 
rate of 550 foot-pounds per second. 

The C. G. S. unit of power is one erg per 
second. 

The practical unit of power is the watt, or 
10,000,000 ergs per second. The kilowatt is 
even more frequently used as the unit of power 
than the watt. (See Power, Unit of.) 

Power, Absorptive The property 



POW.] 42 1 

possessed by many solid bodies of taking in 
and condensing gases within their pores. 

Carbon possesses marked absorptive powers. 
The absorption of gases in this manner by solid 
bodies is known technically as the occlusion of 
gases. (See Gas, Occlusion of.) 

One volume of charcoal, at ordinary tempera- 
tures and pressures, absorbs of 

Ammonia 90 volumes 

Hydrochloric acid 85 " 

Sulphur dioxide 65 " 

Hydrogen sulphide 55 " 

Nitrogen monoxide 40 " 

Carbonic acid gas 35 " 

Ethylene 35 " 

Carbon monoxide 9.42 " 

Oxygen 9.25 " 

Nitrogen 6.50 " 

Hydrogen 1.25 " 

— (Saussure.) 

Power, Candle An intensity of 

light emitted from a luminous body equal to 
the light produced by a standard candle. 
(See Candle, Standard.) 

The light-giving power of one standard 
candle. 

Power, Candle, Nominal A term 

sometimes applied to the candle-power taken 
in a certain favorable direction. 

This term is generally used in arc lighting. 
In the ordinary arc lamp the greatest amount of 
light is emitted at a particular point, viz., from 
the crater in the upper or positive carbon. (See 
Arc, Voltaic.) 

Power, Candle, Rated A term 

sometimes used for nominal candle-power. 

Power, Candle, Spherical The 

average or mean value of candle power 
taken at a number of points around the source 
of light. 

Power, Conducting The ability of 

a given length and area of cross-section of a 
substance for conducting light, heat, elec- 
tricity or magnetism, as compared with an 
equal length and area of cross-section of 
some other substance taken as a standard. 

Power, Conducting, for Electricity 

■ — The ability of a given length and area of 



[Pow. 

cross-section of a substance to conduct elec- 
tricity, as compared with an equal length and 
area of cross-section of some other substance, 
such as pure silver or copper. 

No substance is known that does not offer some 
resistance to the passage of an electric current. 

The following table is taken from Sylvanus P. 
Thompson's "Elementary Lessons in Electricity 
and Magnetism": 



Good Conductors. 



Silver, 
Copper, 



Other metals, 
Charcoal. 



Partial Conductors. 



Water, 
The human 
Cotton, 



body, 



Wood, 

Marble, 

Pape-r. 



Non-conductors. 



Oils, 

Porcelain, 
Dry wood, 
Silk, 
Resins, 



Gutta-percha, 

Shellac, 

Ebonite, 

Parafnne, 

Glass, 



Dry air. 

Heat decreases the conducting power of ele- 
mentary substances. This decrease in the con- 
ducting power is approximately proportional to 
the increase of temperature. Carbon is an ex- 
ception to the law, being a better conductor at a 
red or white heat than when cold. 

The resistance of some alloys, such as German 
silver and platinoid, is but little affected by mod- 
erate changes of temperature. These alloys are, 
therefore, employed in the construction of resist- 
ance coils. 

At a red heat insulators become fairly good 
conductors of electricity. 

At very low temperatures the conducting 
powers of the metals increase. 

Wroblewski has shown that at extremely low 
temperatures copper increases in its conducting 
power for electricity. He cooled copper to — 200 
degrees C, the temperature of the solidification 
of nitrogen, and found that at this temperature 
its conducting power increased to about nine times 
its conducting power at O degrees C. 

It may be remarked here that at exceedingly 
low temperatures a metal would take in or absorb 
heat from the surrounding medium with very 
great rapidity. In this sense it might be said that 



POW.] 422 [Pow. 

its conducting power for heat was greatly in- layer of the conductor, so that the composition of 

creased. the substance is practically of no effect. 

Kohlrausch estimates the conducting power of Hughes has shown that the resistance of an iron 

distilled water at .000000000025, that of mer- telephone line of the usual diameter, to periodic 

cury being taken as unity. currents of about 100 per second, is somewhat 

The best conductors of electricity are the best more than three times its resistance for steady 

conductors of heat. currents. 

This fact is well illustrated by the following There is no such thing as conduction of elec- 
table from Ayrton : tricity in gases. Electricity makes its way through 

a gas by a sudden piercing of the dielectric, or, in 

Relative Conductivities per Cubic Unit. other words, by a disruptive discharge. (See 

Name of Metal. Electricity. Heat. Discharge, Disruptive.) In such a disruptive 

Silver, annealed 100 100 discharge it may be assumed that the gas be- 

Copper, " 94.1 74.8 comes a conductor of electricity while the dis- 

Gold, " 73 54.8 charge is passing. It would then partake of the 

Platinum 16. 6 9.4 nature of an electrolytic conductor, since the dis- 

T ron 1 r r I0 .i charge takes place by means of a true locomotion 

r£^ n j j . j- . of atoms. (See Conduction, Electrolytic.) 

^ ead • ' * ^ 6 7 '9 Power, Conducting for Heat The 

ability of a substance to transmit heat through 

The electric conductivity of porous conductors its mass, 

decreases much more rapidly than the heat con- The metals are gQod conductors of heat They 

■'' . , are also good conductors of electricity. The 

Practically perfect insulators for electricity can , ,• r , j , . ; :-.. 

. conducting powers tor heat and electricity are 
be obtained, but are unknown for heat. , ., ,. , A ,, , , , , , 
' . . nearly identical. As the temperature of a body 
Edlund believes the universal ether to be al- .. j ,. r , . . -, 
__ increases, its conducting power for heat is de- 
most a perfect conductor. He bases this belief , ^ u c ^ j. it- 
r creased. Carbon forms an exception to this 
on the phenomena of sun spots, the occurrence of , 
, . , . , . ,. , ' „ , , statement. 

which is almost immediately followed by the ^, T „ r 7 . , r r » r 

j, j lii^ rpj i£ „ w r fo ai across a wa tf f ormec i f a 

occurrence of magnetic disturbances on the , ■ , ,, , r r ^- 1. 

& hojnogeneous material, the exposed faces of which 

. . are of equal extent and are maintained at a con- 

Lodge regards the lumimferous ether as being ^ difference of temperature , takes place in 

almost a perfect non-conductor, because he thinks accordance with the fo i lowing i aws . 
that conductors must be opaque. It may be sug- 

gested in this connection that Edlund's hypothesis M The rate of floW acr0SS a11 Perpendicular 

as to :he conductibility of magnetic effects through sectlons 1S the same - 

the e.her is also capable of an explanation by the ( 2 A uniform drop of temperature occurs 

effects of magnetic induction. fr° m one s * de °^ ^ e wa ^ to trie ot her in the direc- 

The conducting power for alternating currents tion in which the flow « taking place. 

is not the same as for steady currents. When (3.) The rate of flow is proportional to the dif- 

the alternations become very high, the difference ference in temperature. 

between these conducting powers of the metals T he similarity between the laws of the flow of 
becomes almost inappreciable. heat urlder the circumstances just named and the 
Iron is an enormously worse conductor of flow of electricity through a conductor is evident; 
electricity than copper for rapidly alternating the electrical current being the same in all parts 
currents, at least when the alternations are not c f the circuit, a drop of potential occurring in 
too great. When, however, the alternations are the direction in which the current is moving, 
extremely high, such as those which are produced an d the flow being proportional to the difference 
by the discharge of a Leyden jar or lightning f potential, 
flash, the iron is as good a conductor as the cop- 
per. The reason for this is evident. The dis- Power, Conducting 1 , Tables of 

charge in such cases keeps to the extreme outer Tables in which the relative conducting 



Pow.] 



423 



[Pow. 



powers of different substances are given. (See 
Resistance, Tables of.) 

Power, Electric Power developed 

by means of electricity. 

Power, Electric, Distribution of 

The distribution of electric power by means 
of any suitable system of generators, connect- 
ing circuits and electric motors. 

Power, Electric Transmission of 

The transmission of mechanical energy by 
converting it into electric energy at one point 
or end of a line, and reconverting it into 
mechanical energy at some other point on the 
line. (See Energy, Electric, Transmission 
of.) 

Power, Horse A rate of doing work 

equal to 550 foot-pounds per second, or 33,- 
000 foot-pounds per minute. 

1 horse-power=745.94 X 10 7 ergs per second. 
(See Erg.) 
" =745.941 watts. (See Watt.) 

" =42.746 lb. Fahr. heat units 

per min. (See Units, 
Heat.) 
" =23.748 lb. Cent, heat units per 

min. (See Units, Heat.) 

Power, Horse, Electric Such a 

rate of doing electric work as is equal to 
746 watts or 746 volt-coulombs per second. 

This rate is equivalent to 33,000 foot-pounds 
per minute, or 550 foot-pounds per second. 

Just as 1 pound of water raised through the 
vertical distance of I foot requires the expendi- 
ture of a foot-pound of energy, so I coulomb of 
electricity acting through the difference of poten- 
tial of 1 volt requires a certain amount of work 
to be done on it. (See Coulomb. Volt. Po- 
tential, Electric.) 

This amount is called a volt-coulomb or joule, 
and measured in foot-pounds is equal to .737324 
foot-pounds., The volt coulomb, or joule, isthere- 
fore the unit of electric work, just as the foot- 
pound is the unit of mechanical work. 

The electric work of any circuit in joules is 
equal to the product of the volts by the coulombs. 

If we determine the rate per second at which 
the coulomb; pass, and multiply this product by 
the volts, we have a quantity which represents the 
electrical power, or rate of doing electrical work. 



But 1 ampere is equal to 1 coulomb per second; 
therefore, if we multiply the current in am- 
peres by the difference of potential in volts, the 
product is equal to the electrical power or rate of 
doing electrical work. 

The product of an ampere by a volt is called 
a volt-ampere, or a watt. 

One watt = .0013406 horse-power, or 

One horse-power = 745.941 watts. 

C E 
Therefore the electrical horse-power = — j- ' 

where C = the current in amperes and E = the 
difference of potential in volts. 

Power, Multiplying, of Shunt 

(See Shunt, Multiplying Power of.) 

Power of Periodic Current. — (See Cur- 
rent, Periodic, Power of) 

Power, Portative — The carrying 

power of a magnet. (See Magnet, Porta- 
tive Power of.) 

Power, Projecting-, of Magnet The 

power a magnet possesses of throwing or pro- 
jecting its lines of magnetic force across an 
intervening air space or gap. 

The greater the air space the greater the mag- 
netic reluctance, and consequently the greater the 
magnetizing force required to overcome it. Mag- 
nets of great projecting power are generally of 
great length, to accommodate the long coils of 
wire required. 

Power, Kesuscitating-, of Secondary Bat- 
tery Cell The power possessed by an 

apparently completely discharged secondary 
or storage cell of furnishing additional current 
after a protracted rest. 

This resuscitating power is probably due to 
depolarization. It is therefore present in primary 
as well as in secondary batteries. 

Power, Stray That part of the 

power employed in driving a dynamo, which 
is lost through friction, air churning or air 
currents, eddy currents, hysteresis, etc. 

Power, Thermo-Electric A num- 
ber which, when multiplied by the difference 
of temperature of a thermo-electric couple, 
will give the difference of potential thereby 
generated in micro-volts. (See Diagram, 
Thermo-Electric) 



Pow.] 424 [PrL 

Power, Units of Various units em- i metric h.-p., etc. = 42.162 lb. -Fan., heat units 

ployed in the measurement of power. P er mm « 

The following table of units of power is taken " = 23-423 lb. -Cent., heat units 

from Hering's work on dynamo-electric machines. P er mm - 

TT ._, , -n " = 10.621; klg.-Cent., heat 

Unit of Power. / & . ' 

. ,, units per mm. 

1 erg per second. . = .0000001 watt. nr r , 

,f 1A " = .08634 horse-power heat 

1 watt, or 1 volt- * .7 . 

units per mm. 

ampere, or I , _ 

joule per second, 1 horse-power.. ..= 745-94 X io 7 ergs per 

J *. . ' second, 
or 1 volt- coulomb 

, " = 745.941 watts. 

per second = 1 0000000 ergs per second. J ^ J y ^ 

r . , , " = 33000 foot-pounds per min. 

" =44.2304 foot-pounds per °° f; F 

. y " = 4562.33 kilogram - metres 

" =6.11622 kilogram - metres per ™ in * , , 

& " = 42.746 lb. -Fah., heat units 

per min. . 

" =.0573048 lb. -Fah., heat unit p r ™ in ' 

^^ " = 23.748 lb.-Cent., heat units 

per mm. . 

= .318360 lb.-Cent, heatunit per mm 

J J " =10.772 klg. -Cent., heat 

per mm. ". & . 

, , ~ ., , units per min. 

" = .0144402 klgr.-Cent. heat „ r , 

. " = 1.01381; metric horse- 
unit per min. ° J 
. . , power. 
= .0013592 metric horse- f lb ._ F ah., heat 

P ower * unit per min = 17.45 X io 7 ergs per sec. 

= .0013406 horse-power. u = watts< 

1 foot-pound per Q . 

. r * r , " =.23715 metric norse-power. 

min = 226043 ergs per second. , 

7 *1 " = .023394 horse-power. 

= .0226043 watt. 1 lb. Cent, heat 

= .13825 kilogram-metre per unit per min> _ = 3MI x io t ergs per sec. 

mm - " = 31.4109 watts. 

= .00003072 metric horse- „ = .04269 metric horse power. 

P ower - " = .042109 horse-power. 

" = .000030303 horse-power. 1 klgr.-Cent., heat 

I kilogram - metre unit p ernu ; n 69.25 X io 7 ergs per sec. 

per min = 1635000 ergs per second. « , _ 6g#249 watts< 

= -163500 watt. ti = .0941 2 metric horse-power. . 

= 7.23314 foot-pounds per „ = .092835 horse-power. 

min. 

= .0002222 metric horse- Poynting's Law.— (See Law, Poyntings.) 

P ower - Practical Unit of Inductance, or Self- 

« =.0002192 horse-power. Induction.— (See Inductance, or Self-Indue- 

I metric horse- \ J » 

power, or 1 Hon, Practical Unit of ) 

French horse- Practical Unit of Magneto-Motive Force. 

power, or 1 che- —(See Force, Magneto-Motive, Practical 

val-vapeur, or 1 Unit yj 

r>c j * J „„„„,. w ,^7 Practical Units.— (See Units, Practical) 

or 1 Pferdekraft. = 735 75 X io 7 ergs per v J 

second. Pressel. — A press switch or push connected 

= 735-75° watts. to the end of a flexible, pendant conductor. 

= 32549.0 foot-pounds per Pressnre Wires.- (See Wires, Pressure) 
min. 

" = 4500 kilogram-metres per Primary Battery.— (See Battery, Prim- 

min. ary.) 



Pri.] 



425 



[Pro. 



Primary, Breaking the 



-Breaking 



or opening the circuit of the primary of an 
induction coil. (See Pri?nary, The.) 

Primary Coil. — (See Coil, Primary) 

Primary, Making the Closing or 

completing the circuit of the primary of an 
induction coil. (See Primary, The) 

Primary Plate Condenser.— (See Plate, 
Primary, of Condenser.) 

Primary Spiral.— (See Spiral, Primary.) 

Primary, The That conductor in 

an induction coil, or transformer, which re- 
ceives the impressed electromotive force, or 
which carries the inducing current. 

On changes in the current intensity in the 
primary, currents are induced in the secondary. 
(See Induction, Electro -Dynamic. Coil, Induc- 
tion. Transformer. ) 

Prime Conductor. — (See Conductor, 
Prime) 

Prime Motor.— (See Mover, Prime) 
Prime Mover.— (See Mover, Prime) 

Printer, Stock, Callahan's A form 

of printing telegraph used in sending stock 
quotations telegraphically. (See Telegraphy, 
Printing. Ticker, Stock) 

Printer, Stock, Phelps' A form of 

printing telegraph used in sending stock quo- 
tations telegraphically. (See Ticker, Stock. 
Telegraphy, Printing) 

Probe, Electric A metallic con- 
ductor inserted in the body of a patient in 
order to ascertain the exact position of a 
bullet, or other foreign metallic substance. 

Two conductors are placed parallel to each 
other, ajid are separated at the extremity of the 
probe by any suitable insulating material. On 
contact with the metallic substance, an electric 
bell is rung by the closing of the circuit, or the 
same thing is more readily detected by the de- 
flection of the needle of a galvanometer, or by a 
telephone placed in the circuit. 

Process, Electrotyping (See Elec- 

trotyping, or the Electrotype Process) 

Processes of Carbonization.— (See Car- 
bonization, Processes of.) 



Production of Electricity by Light. — 

(See Electricity, Production of, by Light) 

Prognosis, Electric ■ — In electro- 
therapeutics, a prognosis, or prediction of the 
fatal or non-fatal termination of a disease, 
from an electro-diagnosis based on the exag- 
gerated or diminished reactions of the excit- 
able tissues of the body when subjected to 
the varying influences of electric currents. 
(See Diagnosis, Electro) 

Projections, Pacinotti —Radial 

projections or teeth in an armature core ex- 
tending from the central shaft, so as to form 
slots, pockets, or armature chambers, lor the 
reception of the armature coils. 

The term Pacinotti projections was given to 
these teeth because they were first introduced by 
Pacinotti in his dynamo-electric machine. 

Projector, Mangin A special form 

of search light. 

The Mangin reflector consists of a concavo- 
convex mirror, the convex surface of which is 
silvered and acts as a reflector. The radii of 
curvature of the two surfaces are such that the 
light undergoes the two refractions, i. e., on en- 
tering and on passing out of the mirror, in such a 
manner as to pass out of the mirror in absolute 
parallelism, and thus destroy all aberration. 




Fig. 452. Mangin Projector. 

The Mangin projector is shown in longitudinal 
and in cross-section in Fig. 452, and the projector 
B, is placed in one end of the cylinder A, furnished 
with the openings for the ventilation of the cham- 
ber. 

The cylinder is supported on trunnions, and by 
means of screws can be given any desired inclina- 
tion, in a manner which will be readily under- 
stood from an inspection of the drawing. 

The source of light is an arc lamp of the focus- 
ing type. A small disc is placed in front of the 



Pro.] 



426 



[Pul 



arc in order to stop the direct light from the arc 
which would have divergent rays. The door C, 
is formed of a number of cylindrical lenses, placed 
parallel to one another, which cause the rays to 
diverge horizontally, when so desired. 

Prony Brake. — (See Brake, Prony) 

Proportional Coils.— (See Coils, Propor- 
tional) 

Proportionate Arms.— (See Arms, Pro- 
portionate.) 

Proportionate Arms of Electric Bridge. 

— (See Arms, Proportionate) 

Prostration, Electric Physiological 

exhaustion or prostration, resembling that 
produced by sunstroke, resulting from pro- 
longed exposure to the radiation of an unusu- 
ally large voltaic arc. (See Sunstroke, 
Electric.) 

Protection, Electric, of Houses, Ships 

and Buildings Generally Means for 

protection against the destructive effects of a 
lightning discharge, consisting essentially in 
the use of lightning rods. (See Rod, Light- 
ning.) 

Protection, Electric, of Metals 

(See Metals, Electrical Protection of.) 

Protective Sheath. — (See Sheath, Pro- 
tective) 



Protector, Cable 



-A device for the 



safe discharge of the static charge produced 
on the metallic sheathing of a cable, or on 
conductors surrounding or adjacent to the 
cable, consequent on changes in the electro- 
motive force applied to the conducting core of 
such cable. 

The cable protector is provided for the purpose 
of preventing the discharge of the charge from 
piercing and thus injuring the insulation of the 
cable itself. 



Protector, Comb 



-A term some- 



times applied to a lightning protector or ar- 
rester, in which both the line and ground 
plates are furnished with a series of teeth, 
like those on a comb. (See Arrester, Light- 
ning.) 



Protector, Voltaic Battery A de- 
vice for automatically disconnecting a voltaic 
battery, whenever the circuit in which it is 
placed becomes grounded. 

The battery protector is used in systems of elec- 
tric gaslighting, where, unless great care is exer- 
cised in insulating the circuits, considerable annoy- 
ance is often experienced from the readiness with 
which grounds are established. This arises from 
the high electromotive force of the spark ob- 
tained from the spark coil, piercing the insula- 
tion and establishing a ground through the gas- 
pipes. 

Protoplasm, Effects of Electric Currents 

on Contractions observed in all pro- 
toplasm on the passage of an electric current 
through it. 

Protoplasm, the basis of plant and animal life, 
or the jelly-like matter that fills all organic cells, 
whatever may be the origin of such cells, suffers 
contraction when traversed by an electric cur- 
rent. 

An increased activity in the movements of a. 
form of microscopic life called the amceba is occa- 
sioned by slight shocks from an induction coil ; 
stronger discharges produce tetanic contractions, 
with, in some cases, expulsion of food or even of 
the nucleus. A uniform strength of current pro- 
duces contraction and imperfect tetanus. 

Pull. — A contact maker, similar in general, 
construction to a push button, but operated 
by means of a pulling rather than a pushing 
force. 

The pull is preferable to the push in exposed 
positions, such as outer doors, where moisture is 
apt to injure pushes. 

Pull, Chain A chain pendant at- 
tached to a pendant burner for the move- 
ment of the wipe-spark spring and the 
ratchet in an electrically lighted gas burner. 

Pull, Door Bell, Electric A cir- 
cuit-closing device attached to a bell pull and 
operated by the ordinary motion of the pull. 

Pull, Electric Bell A circuit-clos- 
ing device operated by a pull. 

Fig 453 shows a form of electric bell pull. On 
pulling the bell handle, contact springs, that 
rest on a ring of insulating material when the 



Pul.] 



427 



[Pum, 



pull is in its normal position, are brought into con- 
tact with a metal ring, thus completing the cir- 




Fig. 453. Electric Bell Pull. 

cuit. The bell pull is often used to replace the 
ordinary push button. 

Pulley, Driven A pulley attached 

to the driven shaft. (See Mover, Prime?) 

Pulley, Driving A pulley attached 

to the driving shaft. (See Mover, Prime?) 

Pulsating Current. — (See Current, Pul- 
sating) 

Pulsation. — A quantity of the nature of 
an angular velocity, equal to 2 ^ multiplied 
by the frequency of the oscillation, or, equal 
to 2 it divided by the duration of a single 
period. 

Pulsatory Current. — (See Current, Pul- 
satory?) 

Pulsatory Magnetic Field. — (See Field, 
Magnetic, Pulsatory?) 



-An electric oscil- 



Pulse, Electrical — 

lation. 

A momentary flow of electricity from a 
conductor, which gradually varies from the 
zero value to the maximum, and then to the 
zero value again, like a pulse or vibration in 
an elastic medium. 

Electric pulses are set up in conductors con- 
nected with the coatings of a Leyden jar, on the 
discharge of the same. Such pulses produce a 
series of electrical oscillations, which move alter- 
nately backwards and forwards, until the dis- 
charge is gradually dissipated. (See Oscillations, 
Electric. ) 

The circumstances influencing the rate of 
propagation of an electric pulse through different 
parts of a closed circuit, according to Lodge, are — 



(1.) The extra inertia, or the so-called magnetic 
susceptibility in the conducting substance, es- 
pecially at its outer parts. 

(2.) An undue constriction or throttling of the 
medium through which the disturbance is pass- 
ing. 

(3.) The nature of the insulating medium. 

Pump, Air, Geissler Mercurial 

A mercurial air pump, in which the vacuum 
is attained by the aid of a Torricellian vacuum. 

In the Geissler Mercury Pump y Fig. 454, a 
vacuum is obtained by means of the Torricellian 
vacuum produced in 
a large glass bulb that 
forms the upper ex- 
tremity of a barome- 
tric column. The 
lower end of this tube 
or column is con- 
nected with a reser- 
voir of mercury by 
means of a flexible 
rubber tube. To fill 
the bulb with mer- 
cury the reservoir is 
raised above its level, 
*". <?., above thirty 
inches, the air it con- 
tains being allowed to 
escape through an 
opening governed by 
a stopcock. The ves- 
sel to be exhausted is 
connected with the 
bulb, and by means 
of a two-way exhaus- 
tion cock, communi- Fig. 434. Geissler' s Mer- 
cation can be made curial Air Pump. 

with the bulb, when it contains a Torricellian 
vacuum, and shut off from it while its air is being 
expelled. 

In actual practice the mercury is mechanically 
pumped into the barometric column, and the 
valves are opened either by hand, or automati- 
cally by electrical means. 




Pump, Air, Mechanical 



-A mechan- 



ical device for exhausting or removing the air 
from any vessel. 

An excellent form of air pump is shown in Fig. 
455, which is a drawing of Bianchi's pump. 

Three valves, all opening upwards, are placed 



Pum.] 



428 



[Pyr. 




Fig. 455. Barrel of 

Bianchi's Air Pump. 



at the top and bottom of the cylinder, and in the 
piston, respectively. These valves are mechan- 
ically opened and closed at the proper moment 
by the movements of the piston, i. e., their action 
is automatic. This enables a much higher vacuum 
to be obtained than when the valves open and 
close by the tension of the air. 

Mechanical pumps are unable to readily pro- 
duce the high vacua employed in most electric 
lamps. Mercury pumps 
are employed for this 
purpose. (See Pwnp t 
Air, Mercurial.') 

Pump, Air, Mer- 
curial A de- 
vice for obtaining a 
high vacuum by the 
use of mercury. 

Mercury pumps are 
in general of two types 
of construction, viz. : 

(1.) The Geissler 
pump. 

(2.) The Sprengel pump. (See Pump, Air, 
Geissler Mercurial. Pump, Air, SprengeFs 
Mercurial.) 

Pump, Air, Sprengel's Mercurial 

A mercurial air pump in which the vacuum 
is obtained by 
means of the fall 
of a stream of mer- 
cury. 

In the Sprengel 
mercury pump, Fig. 
456, the fall of a mer- 
cury stream causes 
the exhaustion of a 
reservoir connected 
with the vertical 
tube, by the mechan- 
ical action of the 
mercury in entang- 
ling bubbles of air. 
These bubbles are 
largest at the begin- 
ning of the exhaus- 
tion, but become 
smaller and smaller Fig. 436. Sprengel' s Mer- 
near the end, until, cur ial Air Pump. 

at last, the characteristic metallic click of mer- 
cury or other liquid falling in a good vacuum 





is heard. The exhaustion may be considered as 
completed when the bubbles entirely disappear 
from the column. 

The Sprengel pump produces a better vacuum 
than the Geissler pump, but is slower in its 
action. 

In actual practice, the mercury that has fallen 
through the tube is again raised to the reservoir 
connected to the drop tube by the action of a 
mechanical pump. 

Pumping 1 of Electric Lights— A term 
sometimes applied to a pulsating or period- 
ical increase and decrease in the brilliancy of 
the light. 

This action is generally due to the periodic slip- 
ping of the belt or other driving mechanism. In 
the case of arc lamps it may also be caused by the 
improper action of the feeding device of the 
lamp. 

Puncture, Electro The application 

of electrolysis to the treatment of aneurisms 
or diseased growths. 

The blood is decomposed by the introduction 
of a fine platinum needle connected with the 
anode of a battery, and insulated, except near its 
point, by a covering of vulcanite. 

The kathode is a sponge-covered metallic plate. 

Puncture, Galvano A term some- 
times applied to electro-puncture. (See 
Puncture, Electro?) 

Punning of Telegraph Pole. — (See Pole, 
Telegraphic, Punning of.) 

Push. — A "frame sometimes applied to a 
push button, or to a floor push. (See Push, 
Floor. Button, Push.) 

Push Button. — (See Button, Push.) 

Push-Button Battler, — (See Rattler, 
Push-Button?) 

Push, Floor A push button placed 

on the floor of a room so as to be readily 
operated by means of the foot. (See But- 
ton, Push.) 

Pyknometer. — A term sometimes used 
for the specific gravity bottle employed in 
determining the specific gravity of a liquid. 

Pyrheliometer. — An apparatus for mea- 
suring the energy of the solar radiation. 



Pjr.] 



429 



[Qua. 



The pyrheliometer consists essentially of a 
short cylinder, the area of whose base is accu- 
rately determined. The cylinder being filled with 
a known weight of water, the water surface is ex- 
posed for a definite time to the sun's radiation, 
and the increase in temperature carefully deter- 
mined. The product of the weight of the water 
thus heated by the increase in degrees, gives 
the number of heat units, from which the total 
energy absorbed is readily calculable. In order 
to avoid loss by reflection or diffusion from the 
water surface, it is covered by a layer of lamp- 
black. (See Units, Heat. Calorimeter.) 

Pyro - Electricity. — (See Electricity, 
Pyro) 
Pyro-Magnetic Generator or Dynamo.— 

(See Generator, Pyro-Magnetic.) 

Pyro-Magnetic Motor. — (See Motor, Pyro- 
Magnetic.) 

Pyrometer. — An instrument for deter- 
mining temperatures higher than those that 
can be readily measured by thermometers. 

Pyrometers are operated in a variety of ways. 
A common method is by the expansion ofa metal 
rod. 

Pyrometer, Siemens' Electric An 

apparatus for the determination of tempera- 



ture by the measurement of the electric resist- 
ance of a platinum wire exposed to the heat 
whose temperature is to be measured, 

The platinum wire is coiled on a cylinder of 
fire-clay, so that its separate convolutions do not 
touch one another. It is protected by a platinum 
shield, and is exposed to the temperature to be 
measured while inside a platinum tube. 

The resistance of the platinum coil at O degree 
C. having been accurately ascertained, the temper- 
ature to which it has been exposed can be calcu- 
lated from the change in its resistance when ex- 
posed to the unknown temperature. 

Pyrometer, Siemens' Water A 

pyrometer employed for determining the tem- 
perature of a furnace, or other intense source 
of heat, by calorimetric methods, /. e., by the 
increase in the temperature of a known 
weight of water, into which a metal cylinder 
of a given weight has been put, after being 
exposed for a given time to the source of 
heat to be measured. 

When copper cylinders are employed, the in- 
strument possesses a range of temperatuie of 
1, 800 degrees F.; when a platinum cylinder is 
used, it has a range of 2,700 degrees F. 



Q 



Q. — A contraction for electric quantity. 

Quad. — A contraction sometimes em- 
ployed in place of quadruplex telegraphy. 
(See Telegraphy, Quadruplex) 

Quadrant. — A term proposed for the unit 
of self-induction. 

An earth quadrant is equal to io 9 centi- 
metres. 

In the United States the word henry is used 
for the unit of self-induction. (See Henry, A.) 

Quadrant Electrometer.— (See Electro- 
meter, Quadrant) 

Quadrant Electroscope, Henley's.— (See 
Electroscope, Quadrant, Henley 's) 

Quadrant, Legal A length equal to 

9,978 kilometres, instead of the assumed 
10,000 kilometres. 



Quadrant, Standard A length equal 

to 10,000 kilometres. 

Quadrature, In A term employed 

to express the fact that one simple periodic 
quantity lags 90 degrees behind another. 

The electromotive force of self-induction is said 
to be in quadrature with the effective electro- 
motive force or current. 

Quadruplex Telegraphy, Bridge Method 

of — (See Telegraphy, Quadruplex, 

Bridge Method of.) 

Qualitative Analysis. — (See Analysis, 
Qualitative.) 

Quality or Timbre of Sound. — (See Sound, 
Quality or Timbre of) 

Quantitative Analysis. — (See Analysis, 
Quantitative) 



Qua.] 



430 



LRatL 



Quantity Armature. — (See Armature, 
Quantity?) 
Quantity, Connection of Battery for 

(See Battery, Connection of, for 

Quantity?) 
Quantity Efficiency of Storage Battery. 

— (See Efficiency, Quantity, of Storage Bat- 
tery) 
Quantity, Unit of Electric A 

definite amount or quantity of electricity 
called the coulomb. (See Coulomb?) 

Although the exact nature of electricity is un- 
known, yet, like a fluid (a liquid or gas), electricity 
can be accurately measured as to quantity. 



A current of I ampere, for example, is a 
current in which one coulomb of electricity passes 
in every second. 

A condenser of the capacity of I farad, is- 
large enough to hold I coulomb of electricity 
if forced into the condenser under an electro- 
motive force of i volt. (See Capacity, Electro- 
static. Ear ad. Volt. Ampere.) 

Quiet Arc. — (See Arc, Quiet) 

Quiet Discharge. — (See Discharge, Si- 
lent.) 

Quicking Solution. — (See Solution? 
Quicking?) 



R. — A contraction used for ohmic resist- 
ance. 

p. — A contraction used for specific resist- 
ance. 

Radial Armature. — (See Armature, 
Radial?) 

Radially Laminated Armature Core. — 
(See Core, Armature, Radially-La?ninated.) 

Radiant Energy. — (See Energy, Radiant?) 

Radiant Matter. — (See Matter, Radiant, 
or Ultra-Gaseous?) 

Radiate. — To transfer energy by means of 
waves. 

Radiating. — Transferring energy by means 
of waves. 

Radiation. — Transference of energy by 
means of waves. 

When an elastic body is set into vibration, 
whether it be the vibrations that produce light, 
heat or electricity, energy is charged on the 
body, and the body will then continue to vibrate 
until it imparts to some medium surrounding it 
an amount of energy exactly equal to that orig- 
inally imparted to itself. 

In the case of a sonorous body the energy is 
transferred from the vibrating body to the air 
around it. For example, in the case of an elastic 
metallic wire set into vibration, the wire will con- 
tinue to vibrate until it does as much work on 
the surrounding air as was originally done on it, 
in order to set it into vibration. 



In the case of a heated body the energy is 
transferred from the body to the luminiierous 
ether around it. For example, in the case of the 
same wire heated above the temperature of the 
air, the energy imparted to the molecules of the 
metal by the source of heat causes them to 
move towards and from one another. These 
to and -fro motions of the molecules cause the 
surrounding ether to be set into waves, and as 
much energy is imparted to the ether, as was 
originally imparted to the wire in order to heat it. 

In the case of a luminous body the energy is 
transferred from the body to the luminiferous 
ether. For example, if the wire is heated to 
luminosity by a certain amount of energy im- 
parted to it, the surrounding ether is now set 
into waves of both light and heat, which differ 
from one another only in their wave length, and 
the luminous body will continue to radiate light 
and heat until it imparts to the surrounding 
ether an amount of energy exactly equal to that 
originally imparted to it. 

So, too, in the case of a body charged with 
electricity. If disruptively discharged, the im- : 
pulsive rush of electricity, so produced, causes the 
energy charged on it to be radiated as electro- 
magnetic waves into the surrounding ether. The 
discharging body is, to all intents and purposes, in 
the same condition as the vibrating elastic wire, 
and dissipates or radiates its energy in much the 
same manner. 

Radiation, Electro-Magnetic — 

The sending- out in all directions from a con" 



Had.] 



431 



[Rad. 



ductor, through which an oscillating discharge 
is passing, of electro-magnetic waves in all 
respects similar to those of light except that 
they are of much greater length. (See Elec- 
tricity, Hertz s Theory of Electro-Magnetic 
Radiations or Waves.) 

Radiation of Electricity. — (See Electri- 
city, Radiation of.) . 

Radiation of Lines of Force.— (See Force, 
Lines of, Radiation of.) 

Radical, Compound — A group of 

unsaturated atoms. 

A group of elementary atoms, some of the 
bonds of which are open, or not connected 
or joined with the bonds of other atoms. 
(See Atomicity.) 

For example, hydroxyl, HO, is a compound 
radical, with one of the two bonds of the diad 
oxygen atom, open or unsaturated. 

Radical, Simple — An unsaturated 

atom with its bond or bonds free. 

A single unsaturated atom as distinguished 
from an unsaturated group of atoms. 

Radicals. — Unsaturated atoms or groups of 
atoms, in which one or more of the bonds are 
left open or free. 

Radicals are either Simple or Compound. 

The radical may be regarded as the basis to 
which other elements may be added, or as the 
nucleus around which they may be grouped. 

Thus H 3 0, forms a complete chemical molecule, 
because the bonds of all its constituent atoms are 
saturated, thus H — O — H. But H — O — , or 
hydroxyl, is a radical, because its oxygen atom 
possesses one unsaturated or free bond. By 
combining with the radical (N0 2 ), it forms nitric 
acid, thus H — O — (N0 8 ) or II N0 8 . 

During electrolysis, the molecules of the elec- 
trolyte are decomposed into two groups of simple 
or compound radicals, called ions. These ions are 
respectively electro-positive and electronegative, 
and are called kathions and anions. (See Ions. 
Electrolysis.) 

Radiometer, Crookes' An appara- 
tus for showing the action of radiant matter 
in producing motion from the effects of the 
reaction of a stream of molecules escaping 
from a number of easily moved heated sur- 
faces. (See Matter, Radia7it, or Ultra- 
Gas eons?) 



Radiometer, Electric, Crookes 



A radiometer in which the repulsion of the 
molecules of the residual atmosphere takes 
place from electrified instead of from heated 
surfaces. (See Radiometer, Crookes .) 

Radio-Micrometer, Boys' An elec- 
trical apparatus for measuring the intensity 
of radiant heat. 

The action of the radio-micrometer depends on 
the deflection, by a magnetic field, of a suspended 
thermo-electric circuit composed of three metals, 
viz.: two bars of antimony and bismuth, or of 
their alloys, which are soldered side by side to 
the end of a minute disc or strip of copper foil, as 
shown in Fig. 457. This disc or foil of copper is 




Boys' Radio- Micrometer. 



provided for the purpose of receiving the radia- 
tion that is to be measured. The upper ends of 
the thermo-couple are soldered to the ends of a 
long, narrow, inverted U-shaped piece of copper 
wire, which completes the thermo-electric circuit. 

The absorption of radiant energy by the cop- 
per disc connected to the thermo-electric couple 
produces an electric current, and the circuit, 
being suspended in a magnetic field, is at once 
deflected to a degree dependent on the intensity 
of the radiation, or of the current generated at 
the thermo-electric junction. 

The means adopted for the suspension of t:.e 
system are s'lown in Figs. 457 and 458. A 
small piece of straight wire is soldered to the up- 



Rad.] 



432 



[Rai« 



QUARTZ 
FIBRE 



771 



GLASS 
TUBE 



COPPER, 
WIRE 



per end of the copper stirrup, which completes 
the thermo-electric circuit. This wire is cemented 
to the lower end of a glass tube, the upper end 
of which is provided with a mirror, and the whole 
suspended, as shown, by a 
quartz fibre in the field of a 
powerful magnet. 

In a radio-micrometer made 
by Prof. Boys, the minuteness of 
the suspended circuit may be 
judged from the following ac- 
tual dimensions, viz.: Thermo- 
electric bars, i x ^ x -^ inch ; 
copper circuit of number 36 
copper wire, 1 inch long and 
about ^5 inch wide ; copper 
heat-receiving surface, black- 
ened on the face exposed to the 
radiation, ^ inch in diameter, 
or^x^j-inch; receiver, -^ inch 
square, -g^ inch thick ; quartz 
fibre 4 inches long, -^^ inch in 
diameter. 

This instrument, when pro- 
perly adjusted for extreme sen- 
sitiveness, should give clear in- c; a i 
dications when the blackened QCzz 

surface is warmed but the Fig. 438. Boys 1 
¥0 uiro on degree Centigrade. It Radio-Micwneter. 
will respond to the heat radiated on the surface 
of a half penny from a candle flame at a dis- 
tance of 1,530 feet. 

In order to avoid the disturbance due to the 
magnetic qualities of the antimony and bismuth 
bars, the central portions of the metallic block, 
inside which the system is suspended, is made 
of iron, as shown by the heavier shading in 
Fig. 457- 

This mass of iron serves as a magnetic screen 
to the thermo-electric bars, but permits the action 
of the field on the circuit. 

Radiophone. — A name sometimes given to 
the photophone. (See Photophone) 

Radiopliony.— The production of sound by 
a body capable of absorbing radiant energy 
when an intermittent beam of light or heat 
falls on it. 

The action of radiant energy, when absorbed 
by matter, is to cause its expansion by the conse- 
quent increase of temperature. This occurs even 
when the body is but momentarily exposed to a 



flash of light, but the instantaneous expansion 
thus produced immediately dies away, and by 
itself is indistinguishable. If, however, a suffi- 
ciently rapid succession of such flashes fall on the 
body, the instantaneous expansions and contrac- 
tions produce an appreciable musical note. 

The sounds so produced have been utilized by 
Bell and Tainter in the construction of the Phtto- 
phone. (See Photophone.) 

Railroad, Electric A railroad, or 

railway, the cars on which are driven or pro- 
pelled by means of electric motors connected 
with the cars. 

The electric current that drives the motor is 
derived either from storage batteries placed on 
the cars, or from a dynamo-electric machine, or 
battery of dynamo-electric machines, conveniently 
situated at some point on the road. The current 
from the dynamo is led along the line by suitable 
electric conductors and is passed into the electric 
motor as the car runs along the tracks in various 
ways, viz. : 

Systems for the electric propulsion of cars may, 
therefore, be divided into the dependent system, in 
which the driving current is obtained from conduc- 
tors placed somewhere outside the cars, and the 
independent system, where the current is derived 
from primary or secondary batteries placed on 
the cars. (See Railroads, Electric, Dependent 
System of Motive Power for. Railroads, Electric, 
Independent System of Motive Power for.) 

In the dependent system, the conductors which 
supply the car with current are placed either 
overhead, on the surface of the road-bed or un- 
derground. Thus arise three divisions of the 
dependent system: 

(1.) The Surface System. 

(2.) The Underground System. 

(3. ) The Overhead System. 

(1.) The Surface System. — By placing one or 
both rails in the circuit of the dynamo and taking 
the current from the tracks by means of sliding 
or rolling contacts connected with the motor. 

(2. ) The Underground System. — By placing the 
conducting wires parallel to each other in a longi. 
tudinally slotted underground conduit in the road- 
bed, and provided with two central plates, insu- 
lated from one another and connected respectively 
to the motor terminals, and taking the current 
by means of a traveling brush or roller, called a 
plow, sled or shoe. On the movement of the car 
over the track, these traveling contacts touch the 



Rai.] 



433 



[Rai. 



two parallel line conductors in the conduit and 
take the electric current therefrom. (See Plow, 
Sled.) 

(3.) The Overhead System. — By placing the 
fine conductors on poles along the road, and 
taking the current therefrom by means of suitable 
traveling contacts called trolleys, or by sliders. 

Where a single conductor is employed, the re- 
turn conductor generally consists of the track 
itself, or of the track and ground. (See Trolley.) 

The first method, viz., that of using the tracks 
alone as conductors, is not much employed. 

The use of the track and ground as a return for 
the current is now very generally employed. 

In some systems the track is divided into sec- 
tions which are successively brought into connec- 
tion with the main conductors by contacts effected 
by the attraction between magnets carried on the 
car and contact pieces of magnetic material placed 
below the surface. The rail section thus tempo- 
rarily energized is placed in connection with the 
motor. 

In order to regulate the speed, various devices 
are employed to vary the current strength in the 
motor circuit. These devices consist essentially 
of rheostats or resistances introduced into, or re- 
moved from, the motor circuit on the movement 
by hand of a lever that forms part of the circuit, 
over contact plates connected to the resistance 
coils. 

In order to change the direction of the car, the 
direction of rotation of the electric motor is 
changed. This is effected by some form of re- 
versing gear or mechanism that changes the di- 
rection of rotation of the motor, either by shifting 
the brushes, by changing the field, or by any 
other means. (See Telpherage. Motor, Elec- 
tric. Rheostat.) 

Railroads, Absolute Block System for 

A block system in which one train 

only is permitted to occupy a given block at 
any time. (See Railroads, Block System for.) 

Railroads, Automatic Electric Safety Sys- 
tem for A system for automatically 

preventing the approach of two trains at any 
speed beyond a predetermined distance of 
each other. 

The system consists essentially in the automatic 
closing of the circuit of an electric motor placed, 
on the locomotive between the steam dome and 
the sand box. This motor is in circuit with a 
local battery placed on the cow-catcher, and in- 



troduced in the circuit of the motor by a magnet 
placed on the cow-catcher, as shown in Fig. 459, 




Fig. 45Q. Locomotive with Safety System. 

which represents a locomotive provided with this 
system. 

The magnet is on open circuit with generators 
p'aced on the rear car of a second train, or with 
generators at a bridge or crossing. 

By means of double sectional-conductors placed 
along the track, the generators are automatically 
closed through the magnet, one conductor being 
in permanent connection with the magnet, while 
the other is connected to the generator in the rear 
car of a second train, at a switch or crossing. The 
other terminals of the magnet and generators are in 
permanent electricial connection with the rails, 
which are employed as return ground conductors. 

Fig. 460 shows the application of the safety 
electric system to a bridge. 




Fig. 460. Safety System for Bridge. 

Fig. 461 shows the application of the safety 
system at grade crossing. 




Fig. 461. Safety System for Grade Crossing. 

The author is indebted to Mr. E. P. Thompson 
for cuts and general description. 

Railroads, Block System for —A sys- 
tem for securing safety from collisions of mov- 
ing railroad trains by dividing the road into a 
number of blocks or sections of a given 
length, and so maintaining telegraphic com- 
munication between towers located at the 
ends of each of such blocks as to prevent, 



Rai.] 



434 



[Rai* 



by the display of suitable signals, more than 
one train or engine from being on the same 
block at the same time. 

There are two kinds of railway block systems 
in common use, viz.: 

(i.) The Absolute Block System. 

(2.) The Permissive Block System. 

In the absolute system, which is the safer, one 
train only is permitted on any particular block at 
a given time. 

In the permissive block system more than one 
train is permitted, under certain circumstances 
and conditions, to occupy the same block simul- 
taneously, each train then being notified of the 
fact that it is not alone on the block. 

The absolute block system, though expensive 
to construct and maintain, is the only one that 
should be permitted by law to exist on roads whose 
traffic exceeds a certain amount. 

An absolute block system is employed on the 
London Underground Railroad, and on the Penn- 
sylvania Railroad Systems. 

The system in use on the New York Division 
of the Pennsylvania Railroad is as follows : 

The road between Philadelphia and Jersey City 
is divided into some seventy sections, the length 
of each section being dependent on the amount of 




Fig. 462. Block Tower. 

daily traffic * thus, between Jersey City and New- 
ark, where the traffic is great, there are some 
fifteen sections, although the distance is only 7.9 
miles. 

In each block-tower there are connections with 
three separate and distinct telegraph lines or cir- 
cuits, viz.: 

(1.) A line or wire called the train wire, con- 
necting the block-tower with the General Dis- 
patcher's office at Jersey City. This line is used 
for sending train orders only. 

(2.) A line or wire called the block wire, con- 



necting each block-tower with the next tower on 
each side of it. 

(3.) A line or wire called the message wire, and 
used for local traffic or business. 

The general arrangement of the block -tower is 
shown in Fig. 462. 

Each of the block-towers is sufficiently elevated 
above the road-bed to afford the operator an un- 
obstructed view of the tracks. 

The operator, having ascertained the actual 
condition of the track, either by observation or by 
telegraphic communication with the stations on 
either side of him, gives notice of this condition to 
all trains passing his station by the display of 
certain semaphore signals. 

The semaphore signals as used on the Penn- 
sylvania Railroad are shown in Figs. 463 and 464. 

The form shown in Fig. 463 is used in the abso- 




Fig. 463. Semaphore Signal — Absolute System, 

lute system, and that shown in Fig. 464m the per- 
missive system. These signals consist essentially 
of an upright support provided with a movable 
arm A B, called the semaphore arm, capable of 
being set in any of two or three positions. The 
semaphore signal is placed outside the signal 
tower, often several hundred feet away, but is 
readily set from the tower in any of the desired 
positions by the operator, by the movement of 
rods connected with levers. 

In the permissive system, the semaphore arm 
can be set in three positions, viz.: 

(1.) In a horizontal position, or where the 
semaphore arm makes an angle of 90 degrees with 
the upright. 

(2.) Or it may be. dropped down from the 
horizontal position through an angle of 75 
degrees, as shown in Fig. 463. 

(3.) Or it may occupy a position exactly inter- 



Eai.] 



435 



[Rai. 



mediate between the first and second, or 3 7° 30' 
below the horizontal, as shown in Fig. 464. 

Position No. I is the danger signal, and when 
it is displayed the train may not enter the block 
it governs. 

Position No. 2 shows that the track is clear, 
and that the train may safely enter the block it 
governs. 

Position No. 3, which is used in the permissive 
block system, only signifies caution, and permits 
the train to cautiously enter the block and look 
out for further signals. 

The semaphore arm consists of a light wooden 
-arm, 11 inches wide by 5^ feet in length, painted 
-red or other suitable color that can be easily dis- 
tinguished by daylight. 

By night the positions of the semaphore arm 
are indicated by colored lights. These lights are 




Fig. 464. Semaphore Signal — Permissive System. 

operated as follows, viz.: in the absolute system, 
the semaphore arm A B, pivoted at A, bears at 
its shorter end a disc or lens of red glass R, and, 
in the permissive- system, below this another disc 
or lens of green glass G. An oil lantern, pro- 
vided with an uncolored glass lens, is so sup- 
ported on a bracket fastened to the upright that 
when the semaphore arm points to danger the 
red glass is immediately in front of the lantern ; 
when it points to caution, the green glass is in 
front of the lantern; but when it points to safety, 
the lantern is left uncovered save by its uncolored 
glass. 

At night, therefore, when the semaphore arm 
is set to danger, a red light is displayed; when it 
points to caution, a green light is displayed ; and 
when it points to safety, a white light is displayed . 

In some systems the position of the semaphore 



arm is shown at night by means of light reflected 
from a parabolic mirror, at the focus of which the 
signal lantern is placed. This method possesses 
the advantage over other systems of rendering it 
very improbable that the engineer would mistake 
an ordinary light for a signal light. 

The green light is only used in the permissive 
block system. In the absolute block system, the 
semaphore arm has two positions only ; viz., dan- 
ger, or horizontal, and safety, or 75 degrees below 
the horizontal. 

A single arm is used when it is intended to 
govern a single track only. Where the condition 
of a number of tracks is to be indicated, several 
arms are employed, one above the other. 

When semap ?ore signals are placed on each side 
of a double-track road, the semaphore arm point- 
ing to the right of the vertical support governs 
the line running to the right. 

When the semaphore signals are placed at 
junctions or switch-crossings, the operator in the 
signal-tower opens or closes the switches from 
the tower by the movements of levers that set the 
switches, and then displays the proper semaphore 
signal for that crossing or route ; red, or danger, 
if the route is blocked, and white, or safety, if it 
is clear. Here the interlocking apparatus is em- 
ployed, which consists in devices by means of 
which, when a route has once been set up and a 
signal given for that route, the switches and sig- 
nals are so interlocked that no signal can pos- 
sibly be given for a conflicting route. 

The signals or switches are operated by means 
of iron rods passing over rollers or pulleys. 
These rods are attached by suitable connections 
to the switch or semaphore signals, and are 
operated by means of levers from the signal- 
tower. Switches can be operated as far as 1,000 
feet from the tower; signals as far as 2,500 feet. 

Colored switch- signals are placed opposite the 
end of the switches to indicate the positions of 
the switch. These signals consist of red and 
white discs for day, and a lantern provided with 
red and white glasses for night. When the 
switch on any line is open, the switch-signal shows 
red; when shut, it shows white. These switch- 
signals are only used in the yards. 

No passenger train is permitted on a block, 
after another train has passed the signal station, 
until a dispatch has been received from the 
station ahead that the train has passed and the 
block is thus cleared. 

As an additional precaution against rear col- 



Bai.] 



436 



[Bai. 



lisions, tail-lights are displayed at the ends of the 
trains. These consist of lanterns placed on each 
side of the rear end of the last car. These 
lanterns are furnished with three glass slides. 
The side of the lantern towards the rear of the 
car shows a red light; that to the front and side 
of the car shows a green light. The engineer, 
looking out of the cab, can thus see a green light, 
which serves as a "marker" and indicates to 
him that his train is intact. By day a green flag, 
placed in the same position as the lantern, serves 
the same purpose as a marker. An observer on 
the track, or in the tower, sees the red lights on 
the rear of the train when it has passed. 

Freight trains are now run on separate tracks, 
except in places where the extra tracks are not 
yet completed. Here they do not run on schedule 
time, but are permitted to follow one another at 
intervals that depend on the condition of the 
tracks as shown by the signals displayed. 

Railroads, Electric, Continuous Over- 
head" System of Motive Power for — 

A variety of the dependent system of motive 
power for electric railroads in which a con- 
tinuous bare conductor is connected with the 
terminals of a generating dynamo, and sup- 
ported overhead by suitable means, and a 
traveling wheel or trolley is moved over the 
same by the motion of the car, in order to 
carry off the current from the line to the car 
motor. (See Railroads, Electric, Dcfte7id* 
ent System of Motive Power for .) 

Railroads, Electric, Continuous Surface 

System of Motive Power for — A 

variety of the dependent system of motive 
power for electric railroads, in which the ter- 
minals of the generating dynamo are con- 
nected to the continuous bare metallic con- 
ductor that extends along the entire track on 
the surface of the roadway or street, and from 
which the current is taken off by means of a 
traveling conductor connected with the mov- 
ing car. (See Railroads, Electric, Continu- 
ous Underground System of Motive Power 
for.) 

Railroads, Electric, Continuous Under- 
ground System of Motive Power for 

A variety of the dependent system of motive 
power for electric railways, in which a con- 
tinuous bare conductor is placed under- 



ground in an open slotted conduit, and the 
current taken off from the same by means of 
sliding or rolling contacts carried on the mov- 
ing car. (See Railroads, Electric, Depend' 
ent System of Motive Power for?) 

Railroads, Electric, Dependent System 

of Motive Power for A term now 

generally used for a system of motive power 
for the propulsion of electric railway cars, in 
which the electric current is taken from wires 
or conductors connected with electric sources 
external to the cars. 

A dependent system of motive power for elec- 
tric railways includes three distinct varieties,, 
namely : 

(i.) The. Underground System. 

(2.) The Surface System. 

(3.) The Overhead System. 

In all of these systems the bare conductor con- 
nected with the terminals of a generating dynamo 
may form either one continuous wire or it can 
be divided into separate portions or sections. 

The underground system embraces two distinct 
varieties : 

1 st. A continuous bare conductor placed in an 
open slotted conduit. 

2d. A sectional bare conductor placed in an 
open slotted conduit. 

In the first variety of the underground system, 
bare conductors are placed in an open slotted 
conduit, and connected with the terminals of a. 
dynamo-electric machine which generates the 
current that is to be employed for the propuLion- 
of the cars. Traveling contacts placed on the 
car and connected with an electric motor, carry 
off the current from the bare conductor by rolling 
or sliding over it. 

In the second variety of the underground sys- 
tem, a section of a bare conductor, or bare metal- 
lic points that, on the passage of the car over 
them are automatically connected with the gen- 
erating dynamo, replace the continuous metallic 
conductors of the first system. 

In the surface system, the wires or conductors 
that are connected with the generating dynamo, 
instead of being placed in the underground open 
slotted conduit, are placed directly on the surface 
of the street or roadbed and the current carried 
off from the same by suitable contacts placed on 
the car. 

In most cases, however, in which the surface 
system is adopted, the conductors that are con- 



Rai.] 



437 



[RaU 



nected with the generating dynamo do not ex- 
tend throughout the entire length of the track, 
but are limited to sections of the track that are 
suitably connected with the generating dynamo. 
In some of these systems arrangements are 
devised, by which the car, as it passes over the 
track, automatically connects these sections with 
the generating dynamo while passing over the 
same, and disconnects them after such sections 
have been passed. 

The overhead system embraces two varieties: 

(i.) A continuous trolley wire. 

(2.) A divided or sectional trolley wire. 

In the continuous trolley wire system, the cur- 
rent is taken off from the continuous wire by 
means of a trolley wheel that moves over the 
trolley wire. 

Such a system is especially suitable for suburban 
districts or small towns. In such a system the 
trolley wire is connected with a number of feeder 
wires that either extend from the generating sta- 
tion the entire length of the line, and are con- 
nected with such line at suitable points; or, sepa- 
rate feeders extend from the station to points on 
the line where they are tapped into the trolley 
wire. 

In the divided or sectional trolley wire system 
the wire is divided into suitable sections, and 
feeders extend the entire length of the line and 
are connected to the central points of each section ; 
or, the feeders extend the entire length of the 
line and tap into both ends of the section. 

The author is indebted to G. W. Mansfield for 
the principal facts contained in the above descrip- 
tive matter. 

Railroads, Electric, Divided Overhead 
System of Motive Power for A sec- 
tional overhead system of motive power for 
electric railroads. (See Railroads, Electric t 
Sectional Overhead System of Motive Power 
for,) 

Railroads, Electric, Divided Surface 
System of Motive Power for A sec- 
tional system of motive power for electric 
railroads. (See Railroads, Electric, Sec- 
tional Surface System of Motive Power 
for) 

Railroads, Electric, Divided Under- 
ground System of Motive Power for 

— A sectional system of motive power for 
electric railroads. (See Railroads, Electric, 



Sectional Underground System of Motive 
Power for) 

Railroads, Electric, Double-Trolley Sys- 
tem for A system of electric railroad 

propulsion, in which a double trolley is em- 
ployed to take the driving current from two 
overhead trolley wires. 

The double-trolley system differs from the 
single-trolley system in that it employs no earth 
return. The parallel wires also avoid the effects 
of injurious induction in neighboring telegraph 
or telephone wires. (See Railroads, Electric, 
Dependent System of Motive Power for.) 

Railroads, Electric, Independent System 

of Motive Power for A term for the 

electric propulsion of railway cars by means 
of primary or storage batteries placed on the 
car and directly connected with the motor. 

This is called the independent system, because, 
unlike the dependent system, the energy required 
for the propulsion of the car is obtained directly 
from the energy of the electric source placed on 
the car, instead of, as in the dependent system, 
outside of the car. 

Railroads, Electric, Sectional Overhead 

System of Motive Power for A variety 

of the dependent system of motive power for 
electric railroads, in which sections of bare 
conductors are supported overhead on poles 
placed along the railroad track, and the cur- 
rent taken off from the same by means of 
traveling conductors such as the trolley 
wheel, which is moved over the trolley wire 
by the motion of the car. 

Various systems are employed for connecting 
the different sections of the trolley wire by means 
of feeder wires with the generating dynamo. 
(See Railroads, Electric, Dependent System of 
Motive Power for.) 

Railroads, Electric, Sectional Surface 
System of Motive Power for A 

variety of the dependent system of motive 
power for electric railroads in which conduc- 
tors are placed on the roadbed or along the 
track, and the current taken off from the same 
by means of contacts connected with the mov- 
ing car, and so arranged as to automatically 
switch in such bare sections on the passage 



Rai.] 



438 



[Ray. 



of the car over them, and to switch them out 
as the car leaves them. (See Railroads, 
Electric % Dependent System of Motive Power 
for.) 

Railroads, Electric, Sectional Under- 
ground System of Motive Power for 

— A variety of the dependent system of 
motive power for electric railroads in which a 
sectional conductor is placed underground in 
a slotted conduit, and the current taken from 
the same by means of sliding or rolling con- 
tacts connected with the moving car. (See 
Railroads, Electric, Dependent System of 
Motive Power for.) 

Railroads, Electric, Section Line of 

— Any part of the overhead electric conduc- 
tors insulated from other parts so as to permit 
its supply of electric power to be separately 
controlled. 

Railroads, Electric, Signal Service Sys- 
tem for The system of electric signals 

used on railways for ascertaining the condition 
of the roads, sending instructions to engineers, 
and conveying intelligence generally from 
stations along the road to the running trains. 

Railroads, Electric, Single-Trolley Sys- 
tem A system of electric railroad 

propulsion in which a single trolley is em- 
ployed to take the driving current from a 
single overhead trolley wire. 

The earth, or a conductor placed along the 
track on the roadbed, acts as the return. (See 
Railroads, Electric, Dependent System of Mo- 
tive Power for.) 

Railroads, Permissive Block System for 

A block system in which more than 

one train is permitted under given conditions 
to occupy the same block simultaneously. 
(See Railroads, Block System for) 

Railway, Electric An electric rail- 
road. (See Railroad, Electric) 

Range, Molecular The distance at 

which the molecules of matter exert a sensi- 
ble attraction for one another. 

This distance has been estimated in the case of 
zinc and oxygen as equal to about the ten-mil- 
lionth of a millimetre. 



Ratchet-Pendant Argand-Electric Burner. 

— (See Burner, Argand-Electric, Ratchet- 
Pendant) 

Ratchet-Pendant Electric Burner. — (See 
Burner, Ratchet-Pendant, Electric) 

Ratchet-Pendant Electric Candle Burner. 

— (See Burner, Ratchet-Pendant Candle 
Electric) 

Ratio, Telocity A ratio, in the 

nature of a velocity, that exists between the 
dimensions of the electrostatic and the elec- 
tro-magnetic units. 

This ratio will be understood from the com- 
parison of the following units. In each case the 
numerator gives the dimensions in the electro- 
static and the denominator the dimensions in the 
electro-magnetic system : 



Quantity, 



M% ii 



T-i 



M2]J 



= V 



Here the value of the ratio, viz., the length 
divided by the time, is clearly in the nature of a 

velocity, for V = — . 



Potential. 



Capacity, 



M? ii T-i T 



Resistance, 



y& 


3 


-2 


L 


T* ~~ 


L2 


L-i 


T .__ 


f2 



V 



yz 



L T" 1 L2 V 3 " 
A remarkable similarity exists between the 
value of the velocity expressed in C. G. S. units, 
and the velocity of light, which is of great signifi- 
cance in the electro-magnetic theory of light. (See 
Light, MaxwelPs Electro- Magnetic Theory of.) 

The velocity of light is 2.9992 X 10 10 cen- 
timetres per second. 

The velocity ratio, v, is 2.9800 X io 10 centi- 
metres per second. 

Rattler, Push-Button A device 

connected with a push button to show that 
the bell connected at a distant point, in the 
circuit of a push button, rings when the button 
is pressed. 

Ray, Actinic A ray of light or other 

form of radiant energy that possesses the 



Itay.] 



439 



[Rec. 



power of effecting chemical action. (See 
Deco?nposition .) 

All rays of light, and even some of those in- 
visible to the human eye, are actinic to some 
particular chemical substance or another. 
Whether the ether waves produce the effects of 
heat, of light or of chemical decomposition de- 
pends on the nature of the material on which 
they fall, as well as on the character of the waves 
themselves. 

Ray, Electric {Rata torpedo) A 

species of fish named the ray, which, like the 
electric eel, pos- 
sesses the power 
of producing elec- 
tricity. 

The electric or- 
gan is situated at 
the back of the 
head, and consists 
of hundreds of poly- 
gonal, cellular 
laminae, supplied 
with numerous 
nerve fibres, as 
shown in Fig. 465. 
(See Fishes. Elec- 
tric.) 

Rayleigh's 
Form of Clark's 
Standard Voltaic 
Cell.— (See Cell, 
Voltaic, Stand- 
ard, Rayleigh's 

Form of Clark's.) Fig- 46 5- The Raia Torpedo. 

Reaction. — In electro-therapeutics mus- 
cular contractions following the closing or 
opening of an electric circuit. 

Reaction Coil. — (See Coil, Reaction?) 

Reaction of Degeneration.— (See Degen- 
eration, Reaction of.) 

Reaction of Exhaustion. — (See Exhaus- 
tion, Reaction of.) 

Reaction Principle of Dynamo-Electric 
Machines. — (See Machine, Dynamo-Elec- 
tric, Reaction Principle of) 

Reaction Telephone. —(See Telephone, 
Reaction) 




Reaction Time. — (See Time, Reaction) 

Reaction Wheel, Electric (See 

Wheel, Reaction, Electric) 

Reactions, Kathodic and Anodic Electro- 
Diagnostic The reactions which oc- 
cur at the kathode or anode of an electric 
source placed on or over any part of a living 
body. 




Fig. 466. Kathodic and Anodic Reactions. 

Fig. 466, from De Watteville's "Medical Elec- 
tricity" represents what he assumes takes place at 
the points of entrance and exit of the current in a 
nerve submitted to the action of the anode of an 
electric source. Two zones are formed, an anodic 
and a kathodic zone; the virtual anode is formed 
by the portion of the skin nearer the nerve, and 
the virtual kathode by the adjoining muscies. 
There are thus formed two zones of influence — 
one immediately around the anode, called the 
polar or anodic electrotonic zone, and one sur- 
rounding this and including the virtual kathode, 
and called the peripolar, or kathelectrotonic zone. 

Reading* Telescope. — (See Telescope, 
Reading) 
Real Efficiency of Storage Battery. — 

(See Efficiency, Real, of Storage Battery) 

Real Hall Effect— (See Effect, Hall, 
Real) 

Recalescence. — The property, possessed 
by incandescent steel when cooling, of 
again becoming incandescent after a certain 
degree of cooling has been reached. 

The property of recalescence was first pointed 
out by Barrett. 

A steel wire heated at the middle or near one 
end to a bright red, and allowed to cool in 
a dim light, will cool until a low red heat is 
reached, when it will be observed to reheat at 
some point in the originally heated portion. This 
reheating is manifested by a brighter red spot 



Rec. 



440 



[.Rec. 



which moves along the portion originally heated. 
This reheating is called recalescence, and is due 
to latent heat (potential energy), which, disap- 
pearing when the bar was heated, again becomes 
sensible (kinetic energy) on cooling. 

The temperature at which recalescence takes 
place is sensibly the temperature at which heated 
steel regains its magnetizability. 



Received Current. 

ceived.) 



■(See Current, Re- 



Receiver, Gramophone The re- 
ceiver employed in the gramophone. (See 
Gramophone?) 



Receiver, Graphophone 



ceiver employed in the graphophone. 
Phonograph?) 



-The re- 
(See 



-A receiver, 



Receiver, Harmonic — 

employed in systems of harmonic telegraphy, 
consisting of an electro-magnetic reed, tuned 
to vibrate to one note or rate only. (See Te- 
legraphy, Grays Harmonic Multiple.) 

Receiver Magnet. — (See Magnet, Receiv- 
ing^ 

Receiver, Phonographic The ap- 
paratus employed in a telephone, phono- 
graph, graphophone or gramophone for the 
reproduction of articulate speech. (See 
Phonograph.) 



Receiver, Telephonic 

employed in the telephone. 
phone.) 

Receptive Device, Electro 

Device, Electro-Receptive?) 

Receptive Device, Magneto 

Device, Magneto-Receptive?) 



The receiver 
(See Tele- 

(See 

(See 



-The reciprocal of any 



Reciprocal — 

number is the quotient arising from dividing 
unity by that number. 

Thus, for example, the reciprocal of 4, is \ or 
.250. 

The conducting power of any circuit is equal 
to the reciprocal of its resistance ; or, in other 
words, the conducting power is inversely propor- 
tional to the resistance. 



The following table contains the reciprocals 
of the numerals up to 100 : 

TABLE OF RECIPROCALS. 





Re- 




Re- 




Re- 




Re- 




Re- 





cipro- 


No. 


cipro- 


No. 


cipro- 


No. 


cipro- 


No. 


cipro- 


cal. 




cal. 




cal. 




cal. 




cal. 


2 


. 5000 


22 


0-0455 


42 


0.0338 


62 


0.0161 


82 


0.0122 


3 


Q-3333 


2.3 


0.0435 


43 


0.0233 


03 


0159 


«3 


0.0120 


4 


0.2500 


24 


0.0417 


44 


0.0227 


04 


0.0156 


84 


0.0119 


5 


. 2000 


2S 


0.0400 


45 


0.0222 


b.S 


0154 


«S 


0.0118 


b 


0. 1667 


26 


0.0385 


4° 


0.0217 


66 


0.0152 


8b 


0.0116 


7 


0. 1429 


27 


0.0370 


47 


0.0213 


07 


0.0149 


«7 


0.0115 


8 


0.1250 


28 


o-o357 


48 


0.0208 


b8 


0.0147 


88 


0.0114 


9 


O.IIII 


29 


0.0345 


49 


0.0204 


b 9 


0.0145 


89 


0.0112 


10 


0.1000 


3° 


0.0333 


50 


0.0200 


70 


0.0143 


90 


o.oiii 


1 1 


. 0909 


31 


0.0323 


5 1 . 


0.0196 


7i 


0.0141 


9i 


o.orio 


12 


0.0833 


32 


0.0313 


52 


0.0192 


72 


0.0139 


92 


0.0109 


J 3 


0.0769 


33 


00303 


53 


0.0189 


73 


0.0137 


93 


o.oic8 


-M 


0.0714 


34 


0.0294 


54 


0.0185 


74 


0.0135 


94 


0.0106 


I 5 


0.0667 


35 


0286 


55 


0.0182 


75 


0.0133 


95 


0.0105 


10 


0.0625 


3<> 


0.0278 


56 


0.0179 


76 


0.0132 


96 


0.0104 


i7 


0.0588 


37 


0.0270 


57 


0.0175 


77 


0.0130 


97 


0.0103 


18 


0.0556 


3« 


0.0263 


5« 


0.0172 


78 


0.0128 


98 


0.0102 


19 


0.0526 


39 


0.0256 


59 


0.0169 


79 


0.0127 


-)9 


o.oior 


20 


0.0^00 


40 


0.0250 


60 


0.0167 


80 


0.0125 


100 


O.OIOO 


21 


0.0476 


41 


0.0244 


61 


0.0164 


81 


0.0123 







— {Clark 6° Sabine.) 
Recoil Circuit. — (See Circuit, Recoil.) 

Record, Chronograph A record 

made by means of a chronograph for the pur- 
pose of measuring and recording small inter- 
vals of time. (See Chronograph, Electric?) 



Record, Gramophone 



-The irregular 



indentations, cuttings or tracings made by a 
point attached to the diaphragm spoken 
against, and employed in connection with the 
receiving diaphragm for the reproduction of 
articulate speech. 

Record, Graphophone The record 

made by the movement of the diaphragm of 
the graphophone. (See Phonograph.) 

Record, Phonographic The record 

produced in a phonograph, for the subse- 
quent reproduction of audible articulate 
speech. 

Record, Telephonic The record 

produced by the diaphragm of a receiving 
telephone. 

Various methods have been proposed for ob- 
taining telephonic records, but none of them 
have yet been introduced into actual commercial 
use. 

Recorder, Chemical, Bain's An ap- 
paratus for recording the dots and dashes of 



Rec] 



441 



[Rec. 



a Morse telegraphic dispatch, on a sheet of 
chemically prepared paper. 

A fillet of paper soaked in some chemical sub- 
stance, such as ferro-cyanide of potassium, is 
moved at a uniform rate between the two ter- 
minals of the line, one of which is iron tipped, so 
that on the passage of the current, a blue dot, or a 
dash, will be made on the paper according to the 
length of time the current is passing. 

In order to insure a moist condition of the paper 
fillet, some deliquescent salt, like ammonium 
nitrate, is generally mixed with the ferro-cyanide 
of potassium. 




Fig. 467. Bain Recorder. 

A Bain recorder is shown in Fig. 467. A, is 
a drum of brass, tinned on the outside. The 
paper fillet is drawn from the roll and kept 
pressed against the cylinder A, by a small wooden 
roller B. The needle, which is a metallic point, 
is placed m connection with one end of the line 
wire, and the brass drum is connected with the 
other end through the earth. Care must be ob- 
served to connect the needle point with the posi- 
tive electrode, as otherwise the paper will not be 
marked. (See Electrolysis.) 

The Bain recorder is now almost entirely re- 
placed by the Morse sounder. (See Sounder, 
Morse Telegraphic. ) 

Recorder, Morse An apparatus for 

automatically recording the dots and dashes 
of a Morse telegraphic dispatch, on a fillet of 
paper drawn under an indenting or marking 
point on a striking lever, connected with the 
armature of an electro-magnet. 

This apparatus is sometimes called a Morse 
register. 

The Morse recording or registering apparatus 
is shown in Fig. 468. 

The paper fillet passes between a pair of rollers 
r, driven by the clockwork W. The upper roller 
is provided with a groove, so that the movement 
of the stylus at the b.nt end of the' lever L, by the 



electro-magnet M, moving its armature attached 
to the lever L, may indent or emboss the paper 
fillet. When no current is passing, the armature 
of the magnet and the lever L, are drawn back by 
the action of an adjustable spring at n. 




Fig. 468. Morse Recorder. 

In the drawing, the ordinary Morse sounder is 
shown on the right. The sounder has almost 
entirely replaced the recording apparatus. 

Recorder, Siphon An apparatus 

for reoording in ink on a sheet of paper, by 
means of a fine glass siphon supported on a 
fine wire, the message received over a cable. 

One end of the siphon dips in a vessel of ink. 
The record is received on a fillet of paper moved 
mechanically under the siphon. The ink is dis- 
charged from the siphon by electric charges im- 
parted to the ink by a static electric machine. 




Fig. 46 q. The Siphon Recorder. 
In the annexed sketch of the siphon recorder, 
Fig. 469, a light rectangular coil b b, of very fine 
wire, is suspended by a thin wire f f, between the 
poles N, S, of a powerful compound permanent 
magnet, and moving on the vertical axis of the 
supporting wire f f , and adjustable as to tension, 
at h. A stationary soft iron core a, is magnetized 




SIPHON RECORDER 

Fig. 470. Record of Siphon Recorder. 

by induction and strengthens the magnetic field 
of N, S. The cable current is received by the 



Bee] 



442 



[Kef. 



coil b b, through the suspending wire f f, and is 
moved by it to the right or the left, according to 
its direction, to an extent that depends on the 
current strength. 

The fine glass siphon n, which dips into a 
reservoir of ink at m, is capable of movement on 
a vertical axis 1, and is moved backwards or for- 
wards, in one direction by a thread k, attached 



S E T T L ED 
Fig. 47 1. Record of Siphon Recorder. 
to b, and in the opposite direction by a retractile 
spring attached to an arm of the axis 1. 

As the paper is moved under the point of the 
siphon, an irregular curved line is marked thereon. 

Two records as actually received by a siphon 
recorder are shown in the Figs. 470 and 471. 
Movements upwards correspond to the dots, and 
downwards to dashes. 

Rectification of Alcohol, Electric 

— (See Alcohol, Electric Rectification of) 

Rectified. — Turned in one and the same 
direction. 

The alternate currents in a dynamo-electric 
machine are rectified or caused to flow in one and 
the same direction by means of a commutator. 

The word commuted, generally used in this 
connection, would appear to be preferable to the 
word rectified. (See Commutator.) 

Rectilinear Co-ordinates, Abscissa of 

— (S&c Abscissa of Rectilinear Co-ordinates) 

Rectilinear Current. — (See Current, Rec- 
tilinear.) 

Red Heat— (See Heat, Red) 

Red Hot.— (See Hot, Red) 

Rednctenr or Resistance for Yoltmeter. 
— A coil of known resistance as compared 
with the resistance of the coils of a voltmeter, 
and connected with them in series for the 
purpose of increasing the range of the instru- 
ment. (See Voltmeter) 

Reducteur or Shunt for Ammeter. — A 
shunt coil connected in multiple with the coils 
of an ammeter for the purpose of changing 
the value of the readings. 

The ratio of the resistance of the reducteur and 
the ammeter coils is known. A reducteur in- 
creases the range of current measured by the am- 
meter. 



Refining of Metals, Electric The 

renning of metals by the application of elec- 
trolysis. 

When certain precautions are taken, metals 
thrown down from their solutions, are obtained hi 
a chemically pure condition. This fact is utilized 
in the electrical refining of metals. If, for exam- 
ple, a plate of impure copper is to be refined 
electrolytically, it is used as the anode of a copper 
bath, and placed opposite a thin plate of pure cop- 
per forming the kathode. The passage of the 
current gradually dissolves the copper from the 
plate at the anode, and deposits it in a chemically 
pure condition on the plate at the kathode. 

Somewhat similar principle* are employed for 
electrically refining other metals. 

Reflect. — To throw off from a surface, ac- 
cording to the laws of reflection, as of waves 
in an elastic medium. (See Reflection, Laws 
of) 

Reflecting. — Throwing off from a surface, 
according to the laws of reflection. (See 
Reflection, Laws of) 

Reflecting Galvanometer. — (See Gal- 
'vanometer, Reflecti?ig) 

Reflection. — The throwing back of a body 
or wave from a surface at an angle equal to 
that at which it strikes such surface. (See 
Reflection, Laws of) 

Reflection, Laws of The laws gov- 
erning the reflection of light 

(1.) The angle of reflection, or the angle in- 
cluded between the reflected ray and the perpen- 
dicular to the reflecting surface at the point of 
incidence, is equal to the angle of incidence, or 
the angle included between the striking ray and 
the perpendicular to the reflecting surface at the 
point of incidence. 

(2.) The plane of the angle of incidence co- 
incides with the plane of the angle of reflection. 

Reflection of Electro-Magnetic Waves* 

— (See Waves, Electro-Magnetic, Reflection 
of) 

Reflection of Induction. — (See Lnduc- 
tion, Refection of) 

Reflector. — A plane or curved surface, 
capable of regularly reflecting light. 

Reflector, Parabolic A reflector, 



Ref.] 



443 



[Reg. 



or mirror, the reflecting surface of which is 
a paraboloid, or such a surface as would be 
obtained by the revolution of a parabola 
about its axis. 

A parabolic curve, which may be regarded as 
a section of a parabola, is shown in Fig. 472. 
A parabola has the following properties: If lines 
F P, F P, etc., be drawn from the point F, 
called the focus, to any point, P, P, etc., in the 
curve, and the lines Pp, Pp, Pp, etc., be then 
drawn severally parallel to the axis, V M, then 
all such angles, FPp, FPp, will be bisected by 
verticals to tangents at the point P, P, and P. 

Therefore, if a light be placed at the focus of a 
parabolic reflector, all the light reflected from the 
surface of the parabola will pass uff sensibly par- 
allel to the axis V M. 

In Locomotive Headlights, a 
lamp is placed at the focus of 
a parabolic reflector, and the 
parallel beam so obtained is 
utilized for the illumination of 
the track. In a search light an 
electric arc lamp is placed at 
the focus of a parabolic reflec- 
tor, or at the focus of a lens. 

A parabolic reflector is 
used for search lights, some- Fig. 472. Parabolic 
times in connection with an Reflector. 

arc lamp. A focusing arc lamp must be used for 
this purpose, so as to maintain the voltaic arc at 
the focus of the parabolic reflector, notwithstand- 
ing the unequal consumption of the positive and 
negative carbons. (See Arc, Voltaic.) 

Refract. — To change the direction of waves 
in any elastic medium in accordance with 
the laws of refraction. (See Refraction.) 

Refracting. — Changing the direction of 
waves in an elastic medium in accordance 
with the laws of refraction. 

Refraction. — The bending of a ray of 
sound, light, heat, or electro-magnetism at 
the surface of any medium whose density 
differs from that through which such ray 
was previously passing. 

Rays of sound, light, heat or electro-mag- 
netism are transmitted or propagated in straight 
lines as long as the density of the homogeneous 
medium through which they are passing under- 
goes no change. That is, as long as the medium 





W 


p 


w 


s\ p 


V 




p/\ / p 


V 




v 1 P 


V 


M 




f 


p. 




r 


\ P 


V 




pA v 


V 






w 





is homogeneous or isotropic. (See Medium, Iso- 
tropic.) As the rays enter the surface of a 
medium which differs in density from that through 
which they have been passing, they are bent or 
refracted at the surface of such a medium. 

This bending takes place towards a perpen- 
dicular to the refracting surface at the point of in- 
cidence, when the medium into which the rays are 
entering is of greater density than that they are 
leaving, and from the perpendicular when the 
medium they are entering is of less density than 
that they are leaving. 

The refraction or bending of the ray is caused 
by the difference in the velocity with which the 
waves are propagated through the two media. 

There is no refraction or deviation when the 
two rays enter the new medium at right angle i 
to its surface, or when there is no angle of inci- 
dence. 

Refraction, Double ■ — The property 

possessed by certain substances of splitting 
up a ray of light passed through them into 
two separate rays, and thus doubly refracting 
the ray. 

Certain specimens of calc spar possess the prop- 
erty of double refraction. Each of the two rays 
into which the original ray is separated is polar- 
ized. Such calc spar is called doubly refracting 
calc spar. 

Refraction, Double, Electric The 

property of doubly refracting light acquired 
by some transparent substances while in an 
electrostatic or electro-magnetic field. 

Transient or momentary powers of double 
refraction, acquired by a transparent sub- 
stance while placed in an electric field. 

The intensity of double refraction is propor- 
tioned to the square of the electric force. 

The action of an electric field in endowing a 
substance with the power of double refraction 
while kept in such field, is due to the strain pro- 
duced by the electrostatic stress of the field. 

A similar transient power of double refraction 
is acquired by many bodies when subjected to 
the strain produced by a simple mechanical 
stress. 

Refreshing 1 Action of Current. — (See Ac- 
tion, Refreshing, of Current) 

Region, Extra-Polar — A term ap- 
plied in electro-therapeutics to the region 



Beg.J 



444 



[Beg. 



which lies outside or beyond the therapeutic 
electrode. 

The term extra-polar region is used in contra- 
distinction to polar region. (See Region, Polar.') 

Region, Polar — A term applied in 

electro-therapeutics to that region or part of 
the body which lies directly below the thera- 
peutic electrode. 

Register, Double-Pen Telegraphic 

— A telegraphic register provided with two 
separate styluses or pens for recording the 
telegraphic message on a fillet of paper. (See 
Register, Telegraphic!) 

Register, Morse A name sometimes 

given to a Morse recorder. (See Recorder, 
Morse!) 

Register, Telegraphic An appa- 
ratus employed at the receiving end of a tele- 
graphic line for the purpose of obtaining a 
permanent record of the telegraphic dispatch. 

The telegraphic register consists essentially of 
means whereby a fillet or tape of paper is drawn 
mechanically under a pen or stylus attached to 
the armature of an electro -magnet and moving 
therewith. 

The pen or stylus presses against the paper 
whenever the armature is attracted to the elec- 
tro-magnet, and is held there while the cur- 




Fig. d73 Ink- Writing' Register. 

rent is passing through the coils of the electro- 
magnet. By these means the dots and dashes of 
the telegraphic alphabet are recorded on the 
paper fillet as embossed or printed dots and 
dashes. The Morse register is an apparatus of 
this description. (See Recorder \ Morse.) 

A form of ink-writing telegraphic register is 
shown in Fig. 473. It is self-starting. 



Register, Time, for Railroads A 

telegraphic recording apparatus or register 
designed to record all telegraphic messages 
transmitted over a line. 

The record is received on an endless band or 
fillet of paper. It is useful in case of disputes as 
to the time certain messages were sent over the 
line. 

Register, Watchman's Electric 

A device for permanently recording the time 
of a watchman's visit to each of the dif- 
ferent localities he is required to visit at stated 
intervals. 

These registers are of a variety of forms. They 
consist, however, in general, of a drum or disc of 
paper driven by clockwork, on which a mark is 
made by a stylus or pencil, operated on the clos- 
ing of a circuit by the pressing of a push button 
or the pressing of a key by the watchman at each 
station. 

Registering Apparatus, Electric 

(See Apparatus, Registering, Electric.) 

Registering Electrometer. — (See Elec- 
trometer, Registering!) 

Regulable, Automatically — Capa- 
ble of being automatically regulated. (See 
Regulation, Automatic!) 

Regulate, Automatically To regu- 
late in an automatic manner. (See Regula- 
tion, Automatic.) 

Regulation, Automatic Regulation 

automatically effected. 

Regulation, Automatic, of Dynamo-Elec- 
tric Machine Such a regulation of a 

dynamo-electric machine as will automati- 
cally preserve constant either the current or 
the potential difference. 

The automatic regulation of dynamo-electric 
machines may be accomplished in the following 
ways, viz.: 

(i.) By a Compound Winding of the Machine. 

This method is particularly applicable to con- 
stant-potential machines. By this winding, the 
magnetizing effect of the shunt coils is maintained 
approximately constant, while that of the series 
coils varies proportionally to the load on the ma- 
chine. 

The series coils are sometimes wound close to 



Keg.] 



445 



[Reg. 



the poles of the machine, and the shunt coils 
nearer the yoke of the magnets. Custom, how- 
ever, varies in this respect, and very generally 
the shunt coils are placed nearer the poles than 
the series coils. (See Machine, Dynamo- Electric, 
Compound- Wound.) 

(2.) By Shifting the Position of the Collecting 
Brushes. 

In the Thomson-Houston system of current 
regulation, the current is kept practically con- 
stant by the following devices: The collecting 
brushes are fixed to levers moved by the regula- 
tor magnet R, as shown in Fig. 474, the arma- 
ture of which is provided with an opening for the 
entrance of the paraboloidal pole piece A. A 
dash-pot is provided to prevent too sudden move- 
ment. 

When the current is normal, the coil of the 
regulator magnet is short-circuited by contact 
points at S T, which act as a shunt of very low re- 
sistance. These contact points are operated by 
the solenoid coils of the controller, traversed by 
the main current. The cores of this solenoid are 
suspended by a spring. When the current be- 
comes too strong, the contact point is opened, 
and the current, traversing the coil of the regu- 
lar magnet A, attracts its armature, which shifts 
the collecting brushes into a position in which a 
smaller current is taken off. 

A carbon shunt, r, of high resistance, is pro- 
vided to lessen the spark at the contact points S 
T, which occurs on opening the circuit. 




Fig. 474. Thomson- Houston Regulator. 

In operation the contact points are continually 
opening and closing, thus maintaining a practi- 
cally constant current in the external circuit. 

(3.) By the Automatic Variation of a Resist- 
ance shunting the field magnets of the machine, 
as in the Brush system. 

In Fig. 475 the variable resistance C, forms a 
part of the shunt circuit around the field mag- 
nets F M. This resistance is formed of a pile of 
carbon plates. On an increase of the current, 
such, for example, as would result from turning 
out some of the lamps, the electro magnet B, 



placed in the main circuit, attracts its armature 
A, and, compressing the pile of carbon plates C, 
lowers their resistance, thus diverting a propor- 
tionally larger portion of the current from the 
field magnet coils F M, and maintaining the cur- 
rent practically constant. 

In some machines the same thing is done by 
hand, but this is objectionable, since it requires 
the presence of an attendant. 

(4.) By the Introduction of a Variable Resist- 
ance into the shunt circuit of the machine, as in 
the Edison and other systems. 




Fig. 47 J. The Brush Regulator. 

This resistance may be adjusted either auto- 
matically by an electro-magnet whose coils are 
in an independent shunt across the mains, or may 
be operated by hand. 

In Fig. 476, the variable resistance is shown 
at R, the lever switch being in this case operated 
by hand whenever the potential rises or falls be- 
low the proper value. 




Fig. 476. The Edison Regulator . 

The machine shown is thus enabled to main- 
tain a constant potential otl the leads to which the 
lamps L, L, L, etc., are connected in multiple arc. 

(5.) Dynamometric Governing, in which a 
series dynamo is made to yield a constant cur- 
rent by governing the steam engine that drives 
it, by means of a dynamometric governor. This 
governor operates by maintaining a constant 
torque or turning moment, instead of by means of 



Reg.] 



446 



[Rel. 



the usual centrifugal governor which maintains a 
constant speed. 

(6.) Electric Governing of the Driving Engine, 
in which the governor is regulated by the cur- 
rent itself instead of by the speed of rotation, as 
usual. 

Regulation, Hand Such a regula- 
tion of a dynamo-electric machine as will pre- 
serve constant, either the current or the 
potential, said regulation being effected by 
hand as distinguished from automatic regu- 
lation. 

Regulator, Automatic — A device 

for securing automatic regulation as dis- 
tinguished from hand regulation. (See 
Regulation, Hand. Regulation, Automatic?) 

Regulator, Hand — A resistance 

box, the separate coils or resistances of which 
can be readily placed in or removed from a 
circuit by means of a hand-moved switch. 

The term hand regulator is used as distin- 
guished from automatic regulator. (See Regu- 
lator, Automatic. Regulation, Automatic.) 

Regulator Magnet.— (See Magnet, Regu- 
lator?) 

Regulator, Monophotal Arc-Light 

— A term sometimes employed for an electric 
arc lamp in which the whole current passes 
through the arc-regulating mechanism, and 
which is usually operated singly in circuit 
with a dynamo. 

Regulator, Polyphotal Arc-Lamp 

A regulator for an arc lamp suitable for 
maintaining a number of lamps in series cir- 
cuit with the dynamo. 

Polyphotal regulators differ from monophotal 
regulators in that their regulating electro -mag- 
nets are energized by a shunt circuit around the 
electrodes of the lamp, while in monophotal regu- 
lators such electro-magnets are placed in the di- 
rect circuit. The terms monophotal and poly- 
photal are not generally used in America. 

Reguline Electro-Metallurgical Deposit. 

— (See Deposit, Electro- Metallurgical, Reg- 
uline?) 

Rejuvenation of Luminescence. —(See 
Luminescence, Rejuvenation of.) 



Relative Calibration.— (See Calibration, 
Relative?) 

Relay. — An electro-magnet, employed in 
systems of telegraphy, provided with contact 
points placed on a delicately supported arma- 
ture, the movements of which throw a battery, 
called the local battery, into or out of the 
circuit of the receiving apparatus. 

A relay is sometimes called a receiving magnet. 




Fig. 477 ■ Telegraphic Relay. 

The use of a relay permits much smaller cur- 
rents to be used than could otherwise be done, 
since the electric impulses, on reaching a distant 
station, are required to do no other work than 
attracting a delicately poised movable contact, 
and thus, by throwing a local battery into the 
circuit of the receiving apparatus, to cause such 
local battery to perform the work of register- 
ing. Its use is especially required in the Morse 
system of telegraphy in order lo cause the sounder 
to be distinctly heard. 

A form of relay that is much used is shown in 
Fig. 477- 

The electro- magnet M, is wound with many 
turns of very fine wire. In the form used by the 
Western Union Telegraph Company, there are 
about 8, 500 turns, having resistance of 150 ohms. 
A screw m, is provided for moving the electro- 
magnet M, a slight distance in or out, for the pur- 
poses of adjustment. A semi-cylindrical arma- 
ture A, of soft iron, is attached to the insulated 
armature lever a, the lower end of which is sup- 
ported by a steel arbor, which is pivoted between 
two set screws. 

A retractile spring S', regulable at S, is pro- 
vided for moving the armature away from the 
electro-magnet. There are four binding posts, 
two of which are placed in the circuit of the 
electro-magnet, and two in that of the local bat- 
tery. The ends of the line wire are connected 
with the former, and the receiving instrument 
placed in the circuit of the latter. A platinum 



Rel.] 



447 



[Rel. 



contact is placed on the end of a screw supported 
at F, opposite a similar contact, near the end a, 
of the armature iever. The contact is regulable 
by means of a screw c. 

On the energizing of the electro-magnet, the 
attraction of its armature closes the platinum 
contact, and, by thus completing the circuit of the 
local battery, causes an attraction of the armature 
of the receiving apparatus. On the cessation of 
the current in the main line, the spring S', pulls 
the armature away from the magnet, breaks the 
circuit of the local battery, and thus permits a 
similar spring on the receiving instrument to pull 
its armature away. Thus all the movements of 
the armature of the relay are reproduced with in- 
creased intensity by the armature of the receiving 
instrument. 

The connections of the relay to the local bat- 
tery and the registering apparatus, will be better 
understood from an inspection of Fig. 478, which 
represents a form of relay much used in Germany. 



Relay, Differential A telegraphic 




Fig. 478. Telegraphic Relay, Gertuan Pattern. 

The retractile spring f, is regulated by the up- 
and-down movements of its lower support, which 
slides in ihe vertical pillar S. The line wire is 
shown at m m, connected at one end to earth by 
a ground wire. 

The registering apparatus R, is connected in 
the circuit of the local battery L, as shown. 
The contacts are made by the end B, of the lever 
B B', attached to the armature A, of the electro - 
magnet M M. 

Relay Bell.— (See Bell, Relay, Electric.) 

Relay, Box-Sounding 1 Telegraphic 

— A relay the magnet of which is surrounded 
by a resonant case of wood for the purpose 
of increasing the intensity of the sound made 
by the armature of the magnet. 

A form of box-sounding relay is shown in Fig. 
479- 




Fig. 479. Box- Sounding Relay 

relay containing two differentially wound coils 
of wire on its magnet cores. 

When the currents which pass through these 
two coils are of the same strength, there is no 
movement of the armature, since the fields of the 
two coils neutralize each other. 

The differential relay is used in the differential 
method of duplex and quadruplex telegraphy. 
(See Telegraphy, Duplex Differential Method of. 
Telegraphy, Quadruplex Differential Method of '.) 

Relay Mag'net. — A name sometimes given 
to a relay. (See Relay.) 

Relay, Microphone A device for 

automatically repeating a telephonic message 
over another wire. 




U*t 




Fig. 480. Microphone Relay. 
A form of microphone relay is shown in Figs. 
480 and 481. 

Several minute microphones mounted on the 




Fig. 481. Microphone Relay. 

diaphragm of the telephone whose message is to 
be repeated, so vary the resistance of a local bat- 
tery included in their circuit as to automatically 
repeat the articulate speech received. 

The microphones may De connected either in 



ReL] 



448 



[ReL 



multiple arc or in series, as shown respectively to 
the left and right in Fig. 480. 

Relay, Pocket Telegraphic A form 

of telegraphic relay of such small dimensions 
as to permit it to be readily carried in the 
pocket. 

Relay, Polarized A telegraphic re- 
lay provided with a permanently magnetized 
armature in place of the soft iron armature of 
the ordinary instrument. 

In the form of polarized relay shown in Fig. 
482, N S, is a steel magnet, whose magnetism is 
consequently permanent, with its north and south 
poles at N, and S, respectively. The cores of 
the electro-magnet m, m', are of soft iron, and, 
since they rest on the north pole of the permanent 
steel magnet, the poles, brought very near to- 
gether by the armatures at n, n', will be of the 
same polarity as N, when no current is passing 
through the coils m, m' ; but when such current 
does pass, one of these poles becomes of stronger 
north polarity, while the other changes its polar- 
ity to south. 

By these means to-and fro movements of the 
armature lever, with its contact point, are effected 
without the use of a retractile spring ; movement 
in one direction occurring on the closing of the 
circuit due to the electro-magnetism developed 




Fig. 482. Polarized Relay. 

by the coils m, m', and movement in the opposite 
direction, on the losing of this magnetism on 
breaking the circuit, by the permanent magnet- 
ism of the steel magnet N S. 

These movements are imparted to the soft iron 
lever c, c', pivoted at B, and passing between the 
closely approached soft iron poles at n, n'. This 
lever rests at the end c', against a contact point 



when moved in one direction, and against an in- 
sulated point when moved in the opposite direc- 
tion. It rests against the insulated point when 
no current is passing through the coils m, m'. 

If the armature lever were placed in a position 
exactly midway between the poles n, and n', it 
would not move at all, being equally attracted by 
each; but if moved a little nearer one pole than 
the other, it would be attracted to, and rest 
against, the nearer pole. 

When alternating currents are employed on 
the line, the lever c, c', must be adjusted as nearly 
as possible in the middle of the space between n 
and n', in which case it will remain on the side to 
which it was last attracted, until a current in the 
opposite direction moves it to the other side. 

LB 




Fig. 483. A Detail of the Polarized Relay. 

The space between the magnet poles n, n', 
and the contacts of the armature lever at D, and 
D', are shown in detail in Fig. 483, which is a 
plan of Fig. 482. The binding posts for the line 
battery are shown at L B, 1, and 2, and those 
for the local battery at A and B. The dotted 
lines show the connections. 

Since the polarized relay dispenses with the re- 
tractile spring, it is far more sensitive than the 
ordinary instrument. Once adjusted, no further 
regulation is required, in which respect it differs 
very decidedly from non-polarized relays. 

There are other forms of polarized relays, but 
the above will suffice to illustrate the general 
principle of their operation. 

Relay Shunt, Steam's (See Shunt, 

Relay, Steam's?) 

Reluctance, Magnetic A term re- 
cently proposed in place of magnetic resist- 
ance to express the resistance offered by a 



Rel.] 



449 



[Rep. 



medium to the passage through its mass of 
lines of magnetic force. 

The term reluctance, in the sense of resistance 
to passage of lines of magnetic force, has been 
proposed in place of resistance, for the purpose 
of carrying out the conception of regarding the 
flow of lines of force in a magnetic circuit as 
being due to a magneto-motive force, and being 
opposed by a reluctance of the substances form- 
ing such circuit to the passage of such lines. 

According to this conception, 

The magnetic flux = 

The magneto-motive force 
The reluctance. 

Reluctance, Magnetic, Unit of 

Such a magnetic reluctance in a closed cir- 
cuit that permits unit magnetic flux to 
traverse it under the action of unit magneto- 
motive force. 

In present practical work reluctances vary 
from 100,000 to 100,000,000 of the practical 
units. 

Reluctivity. — A term proposed for mag- 
netic reluctance. (See Reluctance, Mag- 
netic!) 

This term is not generally adopted. 

Removable Key Switch. — (See Switch, 
Removable Key!) 

Renovation of Secondary Cell. — (See 
Cell, Secondary or Storage, Renovation of.) 

Renovation of Secondary or Storage 
Cell. — (See Cell, Secondary or Storage, 
Renovation of.) 

Reofore. — A rheophore. (See Rheophore.) 

Repeaters, Telegraphic Tele- 
graphic devices, whereby the relay, sounder 
or registering apparatus, on the opening and 
closing of another circuit, with which it is 
suitably connected, is caused to repeat the 
signals received. 

Repeaters are employed to establish direct 
communication between very distant stations, or 
to connect branch lines to the main line. 

Fig. 484, shows Wood's Button Repeater. This 
repeater consists simply of a three-point switch 
L, capable of being placed on the points 1, 2 and 
3 ; and a ground switch at 4. The circuits are 
arranged between the sounders S, S', relays 



M, M', main batteries B, B", and the two main 
lines E, and W, in the manner shown. 




Fig. 484. Wood's Button Repeater. 

If the lever L, is in the position shown in the 
drawing, the lines E and W, form independent 
circuits. 

If the ground switch 4 is closed, and the lever 
L, is placed on 2, 2, the eastern line repeats into 
the western. If the lever L, is placed on the 
plates 3, 3, the western line repeats into the 
eastern. 

This repeater is non- automatic and can be 
worked in but one direction at a time ; moreover, 
it requires the services of an attendant. 

The automatic repeater can be operated in both 
directions, and dispenses with the constant ser- 
vices of an attendant at the repeating station. 

In sending a dispatch through a repeater, the 
dots and dashes are prolonged so as to give the 
lever of the repeating instrument time in which 
to move backwards and forwards. 




Fig. 483. Hick's Automatic Button Repeater. 

In Hick' 's Automatic Repeater, shown in Fig. 
485, the switch or circuit- changer is automatic in 
its action. 

The relay magnets are shown at M, M', the 
sounders at R and R' ; f, f, are platinum con- 
tacts operated by levers 1 and 1', and L and L', 
are extra local magnets, that act on armatures 



Rep.] 



450 



[Rep, 



placed directly opposite the armatures of the relay 
magnets. 

The extra local magnet L, is cut out of the 
circuit of B', the extra local battery, when the 
main circuit is broken, and the armature is in 
contact with c. As soon as this happens, how- 
ever, the spring s, drawing away the armature, 
and thus opening the short-circuit of no resist- 
ance between c and a, establishes a circuit 
through L. On a, coming in contact with c, the 
circuit is again broken. 

The tension of the spring s, is so regulated that 
a very rapid vibration of a, is maintained so con- 
stantly, that it is impossible to close the main cir- 
cuit when L, is not cut out. The armature a, 
will therefore respond to very weak impulses of 
the relay magnet. 

On breaking the western main circuit N, the 
lever a, vibrates very rapidly. The lever 1, of the 
sounder R, first breaks the circuit of L, and after- 
wards that of the eastern main circuit E, which 
passes through M. Both L' and M', being 
broken, a slight tension of s', will hold a, in 
place, thus avoiding the breaking of the western 
main circuit through the closing of the local cir- 
cuit through R. On the closing of the western 
circuit, the reverse of these operations occurs. 

The author has taken the above explanation 
mainly from Pope's work on " Modern Practice 
of the Electric Telegraph." 

Repeating Sounder. — (See Sounder, Re- 
peating^) 

Replenisher. — A static influence machine 
devised by Sir William 
Thomson for charging 
the quadrants of his 
quadrant electrometer. 

Two brass carriers C 
and D, shown in Fig. 486, 
are electrically fixed to the 
end of the vulcanite rod 
E, which is capable of ro- 
tation by the thumb screw 
at M, in the direction 
shown by the arrow. Hol- 
low metal half-cylinders, 
A and B, act as inductors, 
a strip of brass fixed around 
the edges of a piece of vul- 
canite P, connecting the metallic springs S, and 
S', as shown. 

The action of the replenisher is readily under- 




Fig. 486. The Replen- 
isher. 



stood from the following considerations, as sug- 
gested by Ayrton in his "Practical Electricity " : 

A and B, Fig. 487, are two insulated hollow 
metallic vessels having a small difference of po- 
tential between them, A, being the higher. C, 
and D, are two small uncharged conductors held 
by insulating strings. If C and D, be held near 
A and B, as shown, the potential of C, will, by 
induction, be raised somewhat above that of D, 
so that when connected by a conductor, such as 
fie metallic wire W, a small quantity of positive 
electricity will flow from C, to D, thus leaving D, 
positively, and C, negatively charged. 

If, now, C and D, are removed from W. and 
placed in the bottom of B and A, as shown in 
Fig. 488, the difference of potential between A, 
and B, will be thereby increased, and if they are 
then withdrawn, and totally discharged, and 




Fig. 487. Action of Replenisher. 

again placed in the first position shown, an ad- 
ditional charge can be given to A and B, and this 
can be repeated as often as desired. 

In the replenisher, A and B, correspond to the 
vessels A and B ; the brass carriers C and D, 
to the balls C and D, and the spring S S, and M, 




Fig. 488. Action of Replenisher. 

to the wire W. No initial charge need be given 
to A and B, since they are invariably found to 



Hep.] 



451 



[Res. 



be at a sufficient difference of potential to build 
up the charge. 
Replenishes Carriers of The 

moving conductors of a replenisher which 
carry the charges and thus permit of an ac- 
cumulation of such charges. (See Re- 
plenisher^) 

Repulsion, Electric The mutual 

driving apart or tendency to mutually drive 
apart existing between two similarly charged 
bodies, or the mutual driving apart of similar 
electric charges. 

Repulsion, Electro-Dynamic The 

mutual repulsion between two electric circuits 
whose currents are flowing in opposite direc- 
tions. 

Parallel currents flowing in opposite directions 
repel one another, because their lines of magnetic 
force have the same direction in adjoining parts of 
the circuit. (See Dynamics, Electro.) 

Repulsion, Electro-Magnetic The 

mutual repulsion produced by two similar 
electro-magnetic poles. 

Repulsion, Electrostatic — The 

mutual repulsion produced by two similar 
electric charges. 

Repulsion, Magnetic The mutual 

repulsion exerted between two similar mag- 
netic poles. 

Repulsion, Molecular The mutual 

repulsion existing between molecules arising 
from their kinetic energy. (See Matter, Ki- 
netic Theory of.) 

Residual Atmosphere — (See At?nosfihere, 
Residual.) 

Residual Charge. — (See Charge, Resid- 
ual.) 

Residual Magnetism. — (See Magnetism, 
Residual.) 

Resin. — A general term applied to a variety 
of dried juices of vegetable origin. 

Resins are, in general, transparent, inflamma- 
ble solids, soluble in alcohol, and, in general, 
excellent non-conductors of electricity. Rosin is 
one of the varieties of resin. 

Resinous Electricity. — (See Electricity, 
Resinous.) 

Resistance. — Something placed in a circuit 
for the purpose of opposing the passage or 



flow of the current in the circuit or branches 
of the circuit in which it is placed. 

The electrical resistance of a conductor is 
that quality of the conductor in virtue of 
which there is a fixed numerical ratio be- 
tween the potential difference of the two 
opposing faces of a cubic unit of such con- 
ductor, and the quantity of electricity which 
traverses either face per second, assuming a 
steady flow to take place normal to these 
faces, and to be uniformly distributed over 
them, such flow taking place solely by an elec- 
tromotive force outside the volume considered. 

The term is used in the first definition in the 
concrete sense of something intended for or used 
as a resistance. For the physical definitions and 
facts see Resistance, Electric. 

Gases offer very high resistance to the flow of 
an electric current. Their non-conducting power 
causes the increase of resistance which attends 
the polarization of a voltaic cell. (See Cell, 
Voltaic, Polarization of.) 

Resistances consist of coils, strips, bars or 
spirals of metal, or plates of carbon, or metallic 
powders, powdered or granulated carbon, or 
liquids. 

Resistance, Absolute Unit of The 

one thousand millionth of an ohm. (See 
Ohm. Units, Practical) 

Resistance, Assymmetrical Con- 
ductors or parts of conductors, which offer a 
greater resistance to the flow of an electric 
current in one direction than in another. 

Assymmetrical conductors are unknown, so far 
as structural peculiarities are concerned, but can 
be obtained by the use of counter electromotive 
forces, acting as resistance. This term was pro- 
posed by Wilke in discussing the obtaining of 
continuous currents by commutatorless dynamo- 
electric machines. 

The resistance of the human body is possibly an 
assymmetrical resistance. 

An evident application of an assymmetrical re- 
sistance is to direct alternating currents so as to 
cause the current that passes to flow in and to the 
same direction. 

Resistance, Balanced A resistance 

so placed in a circuit as to be balanced or 
made equal to another resistance connected 
therewith. 



Res.] 



452 



[Res. 



Resistance, Balanced, for Dynamos 

— A resistance that possesses a range suf- 
ficient to balance one dynamo against another 
with which it is desired to run in parallel. 
— ( Urquhart^) 

Resistance Box. — (See Box., Resistance^) 

Resistance Bridge. — (See Bridge, Resist- 
ance^) 

Resistance Coil. — (See Coil. Resistance.) 

Resistance Coil, Standard — (See 

Coil, Resistance, Standard,) 

Resistance, Conductivity The re- 
sistance offered by a substance to electric 
conduction, or to the passage of electricity 
through its mass. 

Resistance, Dielectric —A term 

sometimes employed for the resistance of a 
dielectric to mechanical strains produced by 
electrification. 

The dielectric resistance of the glass, or other 
dielectric of a Leyden jar or condenser, is fre- 
quently overcome by the passage of the charges 
on the conducting surfaces, and the glass is thus 
pierced. 

The term dielectric resistance would appear 
to be badly chosen; for, like all substances, dielec- 
trics possess a true ohmic resistance, which in- 
creases with the increase of length, and decreases 
with the increase of area of cross- section. 

The resistance of the dielectric, however, differs 
from the ordinary ohmic resistance of conductors, 
in that the resistance of the dielectric is suddenly 
overcome, and the discharge passes disruptively 
as a spark. 

Resistance, Effect of Heat on Electric 

Nearly all metallic conductors have 

their electric resistance increased by an in- 
crease of temperature. 

The carbon conductor of an incandescent elec- 
tric lamp, on the contrary, has its resistance 
decreased when raised to electric incandescence. 
The decrease amounts to about three-eighths of its 
resistance when cold. 

The effects of heat on electric resistance may be 
summarized as follows: 

(i.) The electric resistance of metallic conduc- 
tors increases as the temperature rises. In some 
alloys this increase is smalL 

(2.) The electric resistance of electrolytes de- 
creases as the temperature rises. 



(3.) The electric resistance of dielectrics and 
non-conductors decreases as the temperature rises. 

RESISTANCE AND CONDUCTIVITY OF PURE 
COPPER AT DIFFERENT TEMPERATURES. 



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— {Latimer Clark.) 
Resistance, Electric The ratio be- 
tween the electromotive force of a circuit 
and the current that passes therein. 

The reciprocal of electrical conductivity. 
Resistance can be defined as the reciprocal of 
electrical conductivity, because even the best 
electrical conductors possess appreciable resist- 
ance. 

Ordinarily the resistance of a circuit may be 
conveniently regarded as that which opposes or 
resists the passage of the current. Strictly speak- 
ing, however, this is not true, since from O/im's' 
law (See Law of Ohm, or Law of Current 
Strength) 

E 
C = — , from which we obtain 
R 
E 
R = — , which shows that resistance is a 
C 
ratio between the electromotive force that causes 
the current and the current so produced. 

Resistance may be expressed as a velocity. 
The dimensions of resistance in terms of the 
electro-magnetic units are 



(See Units, Electro- Magnetic.) But these are the 
dimensions of a velocity, which is the ratio of the 
distance passed over in unit time. Resistance may 
therefore be expressed as a velocity. 



Res.] 



453 



[Res. 



' ' The resistance known as ' one ohm ' is in- 
tended to be io9 absolute electro-magnetic units, 
and, therefore, is represented by a velocity of io^ 
centimetres or 10,000,000 metres (one earth quad- 
rant) per second." — (Sylvanus Thompson.) 

Resistance may be represented by a velocity, 
one ohm being the resistance of a wire, which, 
if moved through a unit field of force at the rate 
of 1,000,000,000 (io 9 ) centimetres per second will 
have a current of one ampere generated in it. 
{See Resistance, Ohmic. Resistance, Spurious.) 

The true value of the ohm is exactly io 9 centi- 
metres. The material standards employed, i. e., 
the B. A. and "legal " ohms, are not absolutely 
of this value. 

One mil-foot of soft copper at 10.22 degrees C. 
or 50.4 degrees F. has the standard resistance of 
exactly 10 legal ohms ; at 15.56 or 59.9 degrees 
F., it has a resistance of 10.20 legal ohms, and 
at 23.9 degrees C. or 75 degrees F., 10.53 legal 
ohms. 

RESISTANCE. 

Resistance of Wires of Pure Annealed Copper at 0° C. 

(Density = 8.Q.) 



The following table, based on Matthiessen's 
measurements, gives the relative resistances of 
equal lengths and cross-sections of a number of 
different substances used in electricity as com- 
pared with silver. 

LEGAL MICROHMS. 



Names of Metal, 



Silver, annealed.. . 
Copper, annealed. 
Silver, hard drawn 
Copper, h'rd dr'wn 
Gold, annealed. . . . 
Gold, hard drawn. 
Aluminium, ann'ld 

Zinc, pressed 

Platinum, annealed 

Iron, annealed 

Nickel, annealed. . 

Tin, pressed 

Lead, pressed 

German silver 

Antimony, pressed 

Mercury 

Bismuth, pressed. . 



Resistance in Microhms 




at degree C. 








Relative 






Resistance. 


Cubic 
Centimetre. 


Cubic Inch. 




1.504 


0.5921 


1. 


1.598 


0.6292 


1.063 


1.634 


0-6433 


1.086 


1.634 


0.6433 


1.086 


2.058 


0.8102 


1.369 


2.094 


0.8247 


1-393 


2.912 


1. 147 


1-935 


5.626 


2.215 


3-741 


9.057 


3-565 


6.022 


9.716 


3-825 


6.460 


12.47 


4.907 


8.285 


13.21 


5.202 


8.784 


19.63 


7.728 


13-05 


20.93 


8.240 


13.92 


35-5o 


13.98 


23.60 


94-32 


37-15 


62.73 


131-2 


51.65 


87.23 



.2 ri 

u Z 


u 

0) C "1 

« £ S 


gtn in 
es per 
ramme. 
Wire.) 


as 


.5P« g 


v <u ° re 


5 


175 


5-7 


4.4 


135.28 


7-4 


3-9 


106.35 


9-5 


3-4 


80.8 


12.5 


3 


62.93 


16 


2.7 


51 


19.8 


2.4 


40.23 


25 


2.2 


33-82 


29 


2 


27-95 


36 


1.8 


22.7 


44 


1.6 


17-89 


56 


i-5 


15.75 


63 


1.4 


13-7 


73 


i-3 


n.84 


85 


1.2 


10.06 


100 


1.1 


8.47 


119 


1 


6.99 


144 


•9 


5.66 


178 


.8 


4-47 


225 


•7 


2.83 


294 


.0 


2.52 


400 


•5 


1.74 


576 


•4 


I-I75 


902 


•34 


.808 


1251 


•3 


.7181 


1607 


.24 


.4026 


2508 


.2 


.2797 


3614 


.ib 


.179 


559° 


.12 


.1007 


9929 


.1 


.0699 


14369 


.08 


.0447 


24570 


.06 


.0252 


39824 


.04 


• 0112 


88878 



Resistance of Wire of Pure An- 
nealed Copper at O degree C. 



Ohms 

per 

Kilogramme. 



Ohms 


Metres 


per 

Kilometre. 


per 
Ohm. 


.8 
1.06 


1230.5 

944-38 


i-35 
1.80 


722 
563.92 


2-3 

2.8 
3-6 


439-°7 
355-65 
281 


4.2 


236.08 


5-i 
6 o' 3 


195-15 
158.08 


8 


124.9 


9.1 
10.5 
12 


109.75 
95.651 
82.42 


14 


70.247 


17 
20 


59.024 
48.782 


25 


39.5I5 


32 


31.225 


42 
57 


23.9 
17-56 


81 


12.305 


122.4 


8.173 


177.9 
228.5 
357 


5.622 

4-377 
2.801 


5'4 

803.1 


1.945 
1.245 


1428 
2056 


•7 

.486 


3213 


•3" 


5713 
12848 


•173 
.078 



— (Ayr ton.) 

The above resistances are for chemically pure 
substances only. Slight impurities produce a very 
considerable increase in the resistance. 

Resistance, Electric, of Liquids 

The resistance offered by a liquid mass to 
the passage of an elec- + 
trie current. 

As a rule the electric re- 
sistances of liquids, with 
the single exception of mer- 
cury, are enormously high- 
er than those of metallic 
bodies. 

To roughly determine 
the resistance of a liquid, 
a section is taken between 
two parallel metallic plates 
A and B, Fig. 489, placed 
as shown in the figure, and 
an electric current is pass- 
ed between them. 

In order to accurately 
vary the size of the plates p ig' 489- Resistance of 
immersed in the liquid, and Liquid. 

hence the area of cross-section of the liquid con- 
ductor, as well as the distance between the plates, 
— (Hospitaller.) the apparatus shown in Fig. 490 may be used, in 



.00456 
.00784 
.0128 
.0222 
•0365 
.0557 
.088 
.123 
.185 
.278 
.448 
•574 
•763 
1.03 
1.42 
2.02 

3-95 

4.19 
7.21 
12.3 
22.78 
46.81 
110.41 
222.55 
367.2 
895.36 
1,857.6 
4.489 
I4.I79 
29.549 
78,943 
227,515 
142,405 




Ites.] 454 [Res. 

TABLE OF CONDUCTING POWERS AND RESISTANCES IN OHMS— B. A. UNITS. 



Names of Metals. 



Conducting 

i wng v/nc iuui 

pow £*c i° ng weighing 

s one grain 



Silver, annealed 

Silver, hard drawn.. . . 

Copper, annealed 

Copper, hard drawn. . 

Gold, annealed 

Gold, hard drawn 

Aluminium, annealed. 

Zinc, pressed 

Platinum, annealed ... 

Iron, annealed 

Nickel, annealed 

Tin, pressed 

Lead, pressed 

Antimony, pressed . . . 

Bismuth, pressed 

Mercury, liquid 

Platinum - silver, alloy, 

hard or annealed. . . . 
German silver, hard or 

annealed 

Gold, silver, alloy, hard 

or annealed 



Resistance of a 
wire one foot 



99 -55 
77.96 



29.02 



16.81 

13. 11 

12.30 

8.32 

4.62 

1.24 



0.2214 
0.2421 
0.2064 
0.2106 
0.5849 
0.5950 
0.06822 
0.5710 
3-536 
1.2425 
1.0785 
1.317 
3- 2 30 
3-324 
5-054 
18.740 

4-243 

2.652 

2.391 



Resistance of a 

wire one metre 

long weighing 

one gramme. 



0.1544 
0.1689 
0.1440 
0.1469 
o . 4080 
0.4150 
0.05759 
0.3983 
2.464 
0.7522 
0.8666 
0.9184 
2.257 
2-3295 
3-525 
13-071 

2 -959 

1.850 

1.668 



Resistance of a 

wire one foot 

!°ng tuW inch 

in diameter. 



Resistance of a 
wire one metre 
long, one milli- 
metre in diam- 
eter. 



9.936 
9-i5i 
9.718 
9.940 
12.52 
12.74 
17.72 
32.22 
55-09 
59 40 
75-78 
80.36 

"9-39 
216.0 
798.0 
600.0 

143-35 
127.32 
66.10 



0.019^7 

0.02103 

0.02057 

0.02104 

o 02650 

0.02607 

0.03751 

0.07244 

0.1166 

0.1251 

0.1604 

0.1701 

0.2527 

o.457i 
1.689 
1.270 

0.3140 

0.2695 

0.1399 



Approximate 
percentage of 
variation in re- 
sistance for 1 de- 
gree of tempera- 
ture a.t 20 deg. 



o.377 
0.388 



o-355 
0.365 



0.365 
0.387 
0.389 

o.354 
0.072 

0.031 

0.044 
0.065 



which these distances are readily adjustable, as 
shown. 

Resistance, Equivalent A single 

resistance which may replace a number of 
separate resistances in a circuit without alter- 
ing the value of the current traversing it. 

Resistance, Essential — A term 

sometimes used instead of internal resist- 
ance. 




Fig. 4QO. 



Apparatus for Measuring Resistance of 
Liquid. 



— {Jenkin.) 
on placing a piece of muscle, cartilage, vegetable 
tissue, or even a prismatic strip of coagulated 
albumen across these cushions, we observe, that 
very soon after the circuit is closed, there is a 
considerable variation of the current. * * * 
This phenomenon is called ' external secondary 
resistance.' " — {Landois and Sterling.) 

Resistance, Extraordinary A term 

sometimes employed instead of external re- 
sistance. (See Resistance, External Secon- 
dary^) 

Resistance, False A resistance aris- 
ing from a counter electromotive force and 
not directly from the dimensions of the circuit, 
or from its specific resistance. 

The false resistance of any circuit is sometimes 
called its spurious resistance. (See Force, Electro- 
motive ; Counter. Resistance, Spurious.) 



Resistance, External Secondary A 

term proposed by Du Bois Reymond for the 
change in the resistance of a circuit external to 
the electric source when cataphoric action 
takes place. (See Action, Cataphoric^) 

" If the copper electrodes of a constant battery 
be placed in a vessel filled with a solution of 
cupric sulphate and from each electrode there 
projects a cushion saturated with this fluid, then, 



Resistance, Inductionless 



-A term 



sometimes used instead of non-inductive re- 
sistance. (See Resistance, Non-inductive.) 

Resistance, Inductive A resistance 

which possesses self-induction. 

Resistance, Insulation The re- 
sistance of a line or conductor existing be- 
tween the line or conductor and the earth 
through the insulators, or between the two 



Res. 



455 



[Res. 



wires of a cable through the insulating 
material separating them. 

The insulation resistance of a telegraph line is 
the resistance that exists between the line and the 
earth, through its insulators- The insulation re- 
sistance will decrease as the length of line in 
creases, since for any increase in the number of 
poles and insulators there is a proportional in- 
crease in the area of cross-section of the insula- 
ting supports. 

If the insulation resistance is 1,000,000 ohms 
per mile, in a line 200 miles in length, the insula- 
tion resistance is only 5,000 ohms, that is, 

1,000,000 

— == 5,000 ohms. 

200 

Resistance, Joint, of Parallel Circuits 

The joint resistance of two parallel 

circuits is determined by means of the follow- 
ing formula ; 



R 



r + r 



Where R = the joint resistance of any two cir- 
cuits whose separate resistances are respectively 
r and r . 

When there are three resistances r, r and r", 
in parallel, the joint resistance, 

R= . , "/" , .. 

rr -j-rr -f-r r 

(See Circuits, Varieties of. ) 

Resistance, Magnetic The recipro- 
cal of magnetic permeability or conducti- 
bility for lines of magnetic force. 

Resistance offered by a medium to the 
passage of the lines of magnetic force through 
it. 

The magnetic resistance of the circuit of the 
lines of force is reduced by forming the circuit of 
a medium having a high magnetic permeability, 
such as soft iron. This is accomplished by the 
armature or keeper of a magnet, or by the iron in 
an iron-clad magnet. (See Magnet, Iron. Clad.) 

Resistance, Measurement of - 

Methods employed for determining the re- 
sistance of any circuit or part of a circuit. 

Numerous methods are employed for this pur- 
pose. Among these are : 

(1.) The use of a resistance box with a Wheat - 
stone bridge, by opposing or balancing the un- 
known resistance against a known resistance. 
(See Balance, Wheatstone's Electric.) 



(2.) The differential galvanometer. (See Gal- 
vanometer, Differential.) 

(3.) The method of substitution. 

(4.) Comparison of the deflections of a gal- 
vanometer. 

Method of Substitution. — A resistance-box R, 
Fig. 491, galvanometer G, and the resistance x, 
that is to be measured, are placed in the direct 
circuit of the battery B, by means of conductors 
of such thick wire that their resistance can be 
neglected. 

The deflection of the galvanometer is first 
measured with x, in circuit, and no resistance in 
the box R. The resistance x, is then cut out of 
the circuit by placing a thick copper wire across 
the terminals of the mercury cups at mm', and 
resistances unplugged in R, until the same deflec- 
tion is obtained. Then, if the electromotive force 
of the battery has re?nained constant, the resist- 
ances unplugged equal the unknown resistance. 

For full description of the various methods of 
determining resistance the reader is referred to 
'•' Ayr ton's Practical Electricity, *' '■'• Kempe" 1 s 
Handbook of Testing" or other standard books 
on electrical measurements. 



x 



m m' 



U o o o 



^ 



Vj.lt 

B 

Fig. 4Q 1 Substitution Method. 

When several resistances are placed in series in 
any circuit, by measuring the difference of poten- 
tial at their terminals, their values can be deter- 
mined by simple calculation, being directly pro- 
portional to these differences of potential. 

This method is especially applicable to the 
measurement of such low resistances as the arma- 
tures of dynamo-electric machines. 



— Resistance, Non-inductive 



•A re- 



sistance in which self-induction is practically 
absent. 

An incandescent lamp filament is practically a 
non-inductive resistance when compared with a 
coil on the helix of an electro-magnet. 

Resistance of Human Body. — (See Body, 
Human, Resistance of.) 



Res.] 456 [Res. 

Resistance of Toltaic Arc. — (See Arc, Resistance, Specific, of Liquids 

Voltaic, Resistance of.) The resistance of a given length (one centi- 

Resistance, Ohmic The true resist- metre ) and area of cross-section (one square 

ance of a conductor due to its dimensions ce ntimetre) of any liquid as compared with 

and specific conducting power, as distin- ^ resistance of an equal length and cross- 

guished from the spurious resistance produced 1 n ° P ure S1 ver * 

by a counter electromotive force. (See Force, The resistance of a few common liquids and so- 

Electromotive, Counter. Resistance, Spurt- lutions is here given from Lupton: 

0USm ' Water, pure, at 75 degrees C . . 1 . 188 X io 8 ohms, 

The term ohmic resistance must be regarded as £ m e ug 800 000. 

a pleonasm. Its use can only be permitted in Water at 4 degrees C 9.100 X io 6 " 

contradistinction to counter electromotive force Water at 11 degrees C 3.400 X io 5 ** 

resistance. True and spurious resistance would Dilute hydrogen sulphate (sul- 

seem preferable. phuric acid) at 18 degrees 

Resistance or Cell, Selenium A c > 5 V™ cent, acid 4.88 

mass of crystalline selenium, the resistance of ^^^cT ^^eTcent 

which is reduced by placing it in the form of ., gr "' ** per cen ' _ , 

, , j c u j a °id 1.38 ohms. 

narrow strips between the edges of broad xr , . . , , Q , n 

F s rsitric acid at 18 degrees C, 

conducting plates of brass. density , 32 l6l tl 

The selenium employed for this purpose is the Saturated solution of copper 

vitreous variety which has been fused and main- sulphate (blue vitriol) at 10 

tained for several hours at about 220 degrees C, degrees C 29.30 " 

by means of which its resistance is reduced. Saturated solution of zinc sul- 

By exposure to sunlight, the resistance of a phate at 14 degrees C 21.50 " 

selenium cell is decreased fully one-half its re- Hydrochloric acid, 20 per cent. 

sistance in the dark. The selenium cell is used acid, at 18 degrees C 1.34 " 

in the photophone. (See Photophone.) Sal ammoniac, 25 percent, salt 2.53 " 

Resistance or Reducteur for Voltmeter. Common salt > saturated, at 13 

— (See Reducteur or Resistance for Volt- egrees 5.30 

7neter.) It will be observed that the resistance varies 

Resistance, Secondary A term considerably with differences of temperature. 

sometimes used in place of external secon- Resistance, Spurious A false re- 

dary resistance. (See Resistance, External Stance arising from the development of a 

Secondary?) counter electromotive force. (See Resist- 

Resistance Slide.— (See Slide, Resist- ance > -^^Ise. Force, Electromotive, Coun- 

ance) ter ^> 

Resistance, Specific The particular The spurious resistance is also called the false 

resistance which a substance offers to the resistance, in order to distinguish it from the true 

passage of electricity through it. or °hmic resistance. (See Resistance, Electric.) 

In absolute measure, the resistance in ab- Resistance, Standard A resistance 

solute units between the opposite faces of a used for compari son with or the determina- 

centimetre cube of the given substance. tion of unknown resistances. 

In the practical system the resistance given 

in ohms ^ comm ittee appointed by the American Insti- 
tute of Electrical Engineers in 1890 reported the 

Resistance, Specific Conduction following values for the standard resistance of 

A term sometimes used instead of specific copper wire; at O degree C. in B. A. U. and legal 

resistance. (See Resistance, Specific?) ohms, viz.: 



Ees.] 



457 



[Res. 



Standard Resistance at o° C. 

B. A. U. Legal Ohms. 
' ' Meter-millimetre, ' ' 

■« soft copper "... .02057 .02034 

Cubic centimetre. . . .000001616 .000001598 

"Mil-foot" 9.720 9.612 

Resistance, Tables of Tables in 

which the resistance of equal lengths and 
cross-sections of different substances is 
given in ohms, or other units of resistance. 

Resistance Thermometer. — (See Ther- 
mometer, Electric Resistance) 

Resistance, Transition — A term 

sometimes used in electro-therapeutics for a 
change in the value of the resistance caused 
by polarization. 

Whenever an electric current passes through 
a fluid substance and decomposes the fluid, the 
decomposition products collect on the electrodes 
and produce an increase in the resistance of the 
circuit. 

Resistance, True The resistance 

which a conductor offers to the passage of a 
current by reason of its dimensions and spe- 
cific conducting power, as distinguished from 
a spurious resistance produced by a counter 
electromotive force. 

The true resistance is sometimes called the 
ohmic resistance. — (See Resistance, Spurious. 
Resistance, Ohmic.) 

Resistance, Unit of Such a resist- 
ance that unit difference of potential is re- 
quired to cause a current of unit strength 
to pass. (See Ohm. Potential, Electric. 
Potential, Differe?ice of.) 

Resistance, Unit of, Absolute The 

one thousand millionth of an ohm. (See 
Ohm. Units, Practical) 

Resistance, Unit of, Jacobi's The 

electric resistance of 25 feet of a certain 
copper wire weighing 345 grains. 

Another unit of electric resistance proposed 
by Jacobi was the resistance of a copper wire 
one metre in length and one millimetre in diame- 
ter. 

Resistance, Unit of, Matthiessen's 

— The resistance of one statute mile of pure 
annealed copper wire yV inch in diameter at 



15.5 degrees C, and determined by him to be 
13.59 B« A. ohms. 
Resistance, Unit of, Tarley's The 

resistance of one statute mile of a special 
copper wire T \ inch in diameter. 

Varley's unit was afterwards adjusted by him 
to equal 25 Siemens Mercury Units. 

Resistance, Variable A resistance 

the value of which can be readily varied. 
Variable resistances are either : 
(1.) Automatically variable resistances; or 
(2.) Non- automatically variable resistances. 

Resistance, Variable, Automatic 

A resistance the value of which can be auto- 
matically varied. 

A pile of carbon plates resting on one another, 
in loose contact, offers a high resistance, but when 
compressed as by an electro-magnet their resist- 
ance is lowered. Brush employs such an auto- 
matic resistance in the regulation of his dynamo- 
electric machine. (See Regulation, Automatic.) 

Resistance, Variable Non- Automatic 

— A resistance the value of which is regulated 
by hand. (See Rheostat.) 

Resistance, Virtual A term some- 
times employed instead of impedance. (See 
Impedance) 

Resonance, Electric The setting 

up of electric pulses in open-circuited con- 
ductors, by the action of pulses in neighboring 
conductors. 

Electric resonance, like acoustic resonance, 
takes place when a correspondence exists between 
the time-rate of vibration of the body producing 
the resonance, and the body in which the reso- 
nance is produced. In other words, when the 
wave lengths are the same in the two bodies, or 
when the wave length in one is equal to a half 
wave length, or some definite multiple of a half 
wave length of the other. 

Partial resonance may occur, when there is a 
small difference between the wave lengths of the 
two bodies. Beyond certain limits, however, this 
is so small as to be practically absent. 

When an electrical pulse is started in a con- 
ductor by the discharge of a Leyden jar, a side flash 
spark is obtained in the alternative path, between 
the discharge points. The length of this spark has 
its greatest value, when the time required for the 



Res.] 



458 



[Res. 



pulse to travel backwards and forwards along the 
conducting wires, is exactly equal to the time of 
a complete oscillation in the circuit, or when the 
length of the open-circuit wires is equal to half a 
wave length, or some multiple of half a wave 
length. 

The fact that the length of the spark is greatest 
when certain relations exist between the dimen- 
sions of the two circuits, shows that the time-rate 
of an electrical pulse in any circuit depends on 
the dimensions of that circuit. 

In the case of acoustic resonance, in order that 
one tuning fork may be able to excite vibrations in 
another, the fork producing or exciting the vibra- 
tion must be strictly in unison with the fork in 
which the vibrations are excited, and any varia- 
tions produced in the rate of vibration of the 
sounding fork, by overloading it, or, in other 
words, by altering its dimensions, checks the 
effects of its resonance. 

In a similar manner, any alterations in the di- 
mensions of the circuit, checks or diminishes the 
effects of electric reson- 
ance in a neighboring cir- 
cuit, which was previously 
in unison with it. This 
has been experimentally 
shown by Hertz as fol- 
lows: 

An induction coil A, 
Fig. 492, has the terminals 
of its secondary connected 
to an open rectangular cir- 
cuit provided with spark- 
ing terminals, I, and 2, 
called a spark micrometer. 
Under certain conditions, 
when the discharge oc- 
curs at the terminals B, 
of the ordinary discharger, sparks are produced 
by electric resonance in the electric resonator 
formed by the spark micrometer at M. 

Supposing, now, that a certain character of spark 
is obtained at the terminals B, that is, a cei 
tain velocity of electrical pulsations is obtained 
which depends on the nature of the spark; sup- 
pose, moreover, that the dimensions of the spark 
micrometer or electric resonator are such that the 
greatest length of spark is obtained. Then, any 
alteration in the character of these sparks, be- 
tween the terminals at B, varies the intensity of 
the sparks in the spark micrometer. 

If, for example, the apparatus be arranged 




Fig. 402. Electrical 
Resonance. 



as shown in Fig. 493, in which one of the sec- 
ondary terminals of the induction coil has con- 
nected with it a copper wire i g h. The sparks at 
M, decrease considerably. When, however, the 
conductor C, is connected with the free end H, 
of this additional conductor, then this effect is 
not observed, as is shown by the fact that when 
the conductor C, is attached at the point G, it 
produces no effect on it. 



£ 



cc 



x> 



<£ 



x> 



M 

g " » '6 

Fig. 4Q3. Electric Resonance. 



In another experiment with the same apparatus, 
matters may be arranged that the sparks in the 
micrometer circuit pass singly. When, now, an- 
other conductor C, is attached to K, a stream of 
sparks immediately passes. 

It would appear, therefore, from the above ex- 
periments, that when two circuits are taken, 
having as nearly as possible the same vibration 
periods, any alteration in the dimensions of either 
will prevent one from producing electrical reso- 
nance in the other. 

In the above experiments Hertz demonstrated 
the following facts, viz., 

(1.) The sparks in the micrometer circuit are 
smaller when the discharges take place between 
points, or a point and a plate, instead of between 
knobs. 

(2.) The micrometer sparks are feebler in rare- 
fied gas than in air at ordinary pressures. 

(3.) Extremely slight differences in the nature 
of secondary sparks produce considerable differ- 
ence in the length of the micrometer sparks. 

Hertz found the above results were obtained 
when the secondary sparks were of a brilliant 
color, and were attended by a sharp crack. 

(4. ) The length of the spark in the micrometer 



Res.] 



459 



[Ret. 



circuit varies with the length of the micrometer 
circuit. 

This, of course, follows from the fact that any 
alteration of the length in the micrometer circuit, 
produces, by electrical retardation, a correspond- 
ing alteration in the time of the electrical pulses. 

(5.) No effect is produced in the length of the 
micrometer spark by variations in the material, 
the resistance, or the diameter of the wire forming 
the micrometer circuit. 

This is probably because the rate of propaga- 
tion of electrical pulses along a conductor, de- 
pends mainly on the capacity of the conductor, 
and on its co-efficient of self-induction, and only 
to a slight extent on its resistance. 

(6.) The length of wire connecting the microm- 
eter circuit with the secondary circuit has but 
little effect, provided such length does not exceed 
a few metres. 

Local disturbances, therefore, must traverse 
conductors without undergoing any appreciable 
change. 

(7.) The position of the point on the micrometer 
circuit connected with the secondary circuit, is of 
the greatest importance. 

When the point on the micrometer circuit is 
situated symmetrically with respect to the two mi- 
crometer knobs, variations of potential will reach 
the terminals in the same phase, and there will be 
but little effect, as seen by the sparks between the 
micrometer knobs. Such a point on the microm j 
eter knobs is called the null point, or it is called as 
in a corresponding case in acoustics, a nodal point. 
(See Point, Null. Point, Nodal. ) 

(8.) When the conductors are of sufficient 
length, their approach produces disturbances in 
a previously adjusted and quiet spark microm- 
eter, just as the approach of a conductor would. 

Probably one of the most curious effects con- 
nected with the phenomena of electrical resonance 
is that pointed out by Lodge, viz. : that when the 
spark from a secondary circuit is so placed that 
the light is visible from a micrometer circuit, the 
effects of the discharge are greatly increased. 
Lodge also found that the light from burning 
magnesium wire, or, in general, light rich in the 
ultra-violet rays, produces the same effect. 

Resonator, Electric An apparatus 

employed by Hertz in his investigations on 
electric resonance. (See Resonance, Elec- 
tric^) 

An electric resonator consists essentially of an 



open-circuited conductor, or circuit of such dimen- 
sions that electro-magnetic waves or pulses are 
propagated through it at the same rate as those 
which are occurring in a neighboring circuit 
from which electro-magnetic radiation is tak- 
ing place. Under these circumstances electro- 
magnetic pulses are set up sympathetically by 
resonance in the open circuit of the resonator, like 
the sympathetic vibrations in a tuning fork, when 
placed near another vibrating tuning fork, which 
is giving off sound waves of exactly the same 
perLd of vibration as its own. 

.Resonator, Electro-Magnetic A 

term applied to the Hertz spark micrometer, 
in which electro-magnetic waves are produced 
by electric resonance. (See Resonance, Elec- 
tric^) 

Resultant. — In mechanics, a single force 
that represents in direction and intensity the 
effects of two or more separate forces. 

The separate forces are called the components. 
(See Components.) 

Retardation.— A decrease in the speed of 
telegraphic signaling caused either by the 
induction of the line conductor on itself, or 
by mutual induction between it and neighbor- 
ing conductors, or by condenser action, or by 
all. 

The line must receive a certain charge before 
a current sent into it at one end can produce a 
signal at the other end. This charge will de- 
pend on the length and surface of the wire, on the 
neighborhood of the wire to the earth or other 
wires, and on the nature of the insulating mate- 
rial between the wire and neighboring conductors. 
This results in a charge given to the wire which 
is lost as a current for signaling. The greater the 
electrostatic capacity of the line wire, the greater 
will be the retardation in signaling. (See Capa- 
city, Specific Inductive. Dielectric. Capacity, 
Electrostatic. Induction, Electro-Dynamic.) 

Retardation in signaling is produced by the 
following causes : 

(1.) Self-Induction which produces extra cur- 
rents. (See Induction, Self. Currents, Extra.) 

The extra current on making, retards the be- 
ginning of the signal ; the extra current on break- 
ing, retards its stopping. 

(2.) Mutual Induction between the line con- 
ductor and neighboring conductors. 



Ret] 



460 



[Rhe. 



(3.) The Magnetic Inertia or Lag, or the time 
required to magnetize or demagnetize the core of 
the electro -magnetic receptive devices used on 
the line. 

(4.) By Condenser Action, the cable acting as a 
condenser. 



Retardation, Electric 



-A retarda- 



tion in the starting or stopping of an electric 
current, arising from self-induction. (See In- 
duction, Self. Retardation) 

Retardation, Inductive A retarda- 
tion in the appearance of a signal at the dis- 
tant end of a cable, produced by the action of 
induction. (See Retardation.) 

Retardation, Magnetic A retarda- 
tion in the magnetization or demagnetization 
of a substance due to magnetic lag. (See 
Retardation. Lag, Magnetic?) 

Retarding", Electrically Decreas- 
ing the speed of telegraphic signaling, by 
means of induction. (See Retardation) 



Retentivity, Magnetic 



-A term pro- 



posed by Lamont in place of coercive force, 
or the power possessed by a magnetizable 
substance of resisting magnetization or de- 
magnetization. (See Force, Coercive) 

Return Circuit. — (See Circuit, Return) 

Return, Earth (See Earth Re- 
turn) 

Return Ground. — (See Ground-Return) 

Return Wire or Conductor. — (See Wire, 
Return) 

Returns. — In a system of distribution, those 
conductors through which the current flows 
back from the electro-receptive devices to 
the source. (See Leads) 

The word returns is sometimes used in a sys- 
tem of distribution by parallel circuits, to distin- 
guish between the conductor by which the cur- 
rent goes back or returns from the receptive de- 
vices to the dynamo, and the conductor that leads 
it to the receptive devices. The term leads is, 
however, often applied to both conductors. 

Reverse-Induced Current. — (See Current, 
Reverse-Induced) 



Reversed Currents.— (See Currents, Re- 
versed) 

Reverser, Current A switch, or 

other apparatus, designed to reverse the di- 
rection of a current. 

Reversible Bridge. — (See Bridge, Rever- 
sible) 
Reversible Heat— (See Heat, Reversible) 

Reversibility of Dynamo. — The ability 
of a dynamo to operate as a motor when tra- 
versed by an electric current. (See Motor, 
Electric) 

Reversing Gear of Electric Motor.— (See 
Motor, Electric, Reversing Gear of) 

Reversing Key. — (See Key, Reversing) 

Reversing Key of Quadruplex Tele- 
graphic System.— (See Key, Reversing, of 
Quadruplex Telegraphic System) 

Reversing Magnetic Field. — (See Field, 
Magnetic, Reversing.) 

Rheochord. — A word formerly employed 
instead of rheostat. (See Rheostat) 

Rheometer. — A word formerly employed 
for any device for measuring the strength of 
a current. 

This word is now obsolete and is replaced by 
the word galvanometer. (See Galvanometer.) 

Rheomotor. — A word formerly employed 
to designate any electric source. 

This word is now obsolete, and replaced by 
the various names of the different electric sources. 
(See Source, Electric.) 

Rheophore. — A word formerly employed to 
indicate a portion of a circuit conveying a cur- 
rent and capable of deflecting a magnetic 
needle placed near it. (Obsolete.) 

Rheoscope. — A word formerly employed in 
place of the present word galvanoscope, for 
an instrument intended to show the presence 
of a current, or its direction, but not to 
measure its strength. (Obsolete.) 

Rheoscope, Physiological A sensi- 
tive nerve-muscle preparation employed to 
determine the presence of an electric current. 
(See Frog, Galvanoscope) 



Rhe.] 



461 



[Kin. 



A term sometimes applied in electro-thera- 
peutics to the frog's legs preparation adapted 
to show the presence of any electric current. 

The physiological rheoscope is adapted to 
show the presence of an electric current without 
the use of a galvanometer. On the passage of 
the electric current the frog's legs twitch con- 
vulsively. 

Rheostat. — An adjustable resistance. 

A rheostat enables the current to be brought 
to a standard, i. e., to a fixed value, by adjusting 
the resistance; hence the name. 

The term rheostat is applied generally to a 
readily variable resistance, the varying values of 
which are known. 

Rheostat, Dynamo-Balancing An 

adjustable resistance whose range is sufficient 
to balance the current of one dynamo against 
another with which it is required to run in 
parallel. 

Rheostat, Water A rheostat the 

resistance of which is obtained by means of a 
mass of water of fixed dimensions. (See 
Rheostat^) 

Rheostat, Wheatstoire's A form of 

apparatus sometimes employed for an adjust- 
able resistance. 

This apparatus is very seldom employed in 
accurate work. 

The parallel cylinders A and B, Fig. 494, are 
formed respectively of conducting and non-con- 
ducting materials, the bare wire on which can be 
wound from either 
cylinder to the other. 
When introduced into 
a circuit, only the re- 
sistance of that part 
of the wire that is on 
B, is introduced into 
the circuit, since the 
bare wire on A, is 
short-circuited by the 
metallic cylinder. 
This rheostat is not 




Fig. 4g4- IVheat stone' 's 
Rheostat. 



very suitable for accurate measurements, owing 
to the difficulty of invariably obtaining reliable 
contacts. 

Rheostatic Machine. — (See Machine, 
Rheostatic.) 



Rheotome. — A word formerly employed 
for any device by means of which a circuit 
could be periodically interrupted. 

This word is now obsolete, and is replaced by 
interrupter. (See Interrupter.) 

Rheotrope. — A word formerly employed 
for any device by which the current could 
be reversed. 

This word is now obsolete and replaced by 
commutator or current reverser. (See Reverser, 
Current.) 

Rhigolene. — A highly volatile hydro-car- 
bon obtained during the distillation of coal 
oil, and employed in the flashing treatment of 
carbons for incandescent lamps. (See Car- 
bons, Flashing Process for.) 

Rhumbs of Compass. — (See Compass, 
Rhumbs of.) 

Ribbed Armature Core. — (See Core, 
Armature, Ribbed.) 

Ribbon Copper. — (See Copper, Ribbon) 

Right-Handed Solenoid. — (See Solenoid, 
Right-Handed.) 

Right-Hand Trolley Frog.— (See Frog, 
Trolley, Right-Hand.) 

Rigidity, Molecular — Resistance 

offered by the molecules of a substance to 
rotation or displacement. 

The molecular rigidity of a magnetizable sub- 
stance was until recently considered to be the 
cause of the differences of coercive force or mag- 
netic retentivity possessed by different substances. 
The general acceptance of Ewing's theory of 
magnetism has, of course, caused the above view 
to be considerably modified. (See Magnetisiti, 
Ewing 's Theory of. Force, Coercive. Retentiv- 
ity, Magnetic. ) 

Ring, Ampere The turn or turns 

of wire used in electric balances for the meas- 
urement of electric current. 

Ring Armature. — (See Armature, Ring.) 

Ring Armature Core.— (See Core, Arma- 
ture, of Dynamo-Electric Machine.) 

Rings, Electric A term sometimes 

used instead of Nobili's rings. (See Metal- 
lochromes.) 



Bin.] 



462 



[Rod. 



Rings, Electro-Chromic A term 

sometimes applied to metallochromes. (See 
Metallochromes?) 

Rings, Nobili's A term sometimes 

used for metallochromes. (See Metallo- 
chromes.) 

Roaring of Arc. — (See Arc, Roaring of.) 

Rocker Arm. — (See Arm, Rocker.) 

Rocker, Brush In a dynamo-elec- 
tric machine or electric motor, any device for 
shifting the position of the brushes on the 
cummutator cylinder. 

Rocker, Multiple-Pair Brush A 

term sometimes used for multiple-pair brush 
yoke. (See Yoke, Multiple-Pair Brush?) 

Rocker, Single-Brush A device 

by means of which a single pair of brushes 
are so supported on a dynamo-electric ma- 
chine or electric motor, as to be capable 
of being readily shifted into the desired 
position on the commutator cylinder. 

Rocker, Single-Pair Brush — A 

term sometimes used for single-pair brush 
yoke. (See Yoke, Single-Pair Brushy 

Rod Clamp. — (See Clamp, Rod) 

Rod, Clutch A clutch or clamp pro- 
vided in an arc lamp to seize the lamp rod and 
thus arrest its fall, during feeding, beyond a 
certain predetermined point. 

The clutch or clamp is caused to release or hold 
the lamp rod by the action of an electro-magnet 
placed in a shunt circuit around the electrodes. 
(See Lamp, Arc, Electric.') 

Rod, Discharging A jointed rod 

provided at both ends 
with balls and con- 
nected at the middle by 
a swinging joint which 
permits the balls to 
move towards or from 
one another, employed 
for the disruptive dis- 
charge of Leyden bat- 
teries or condensers. 
(See Discharge, Dis- ' ' r oc i. 
ruptive. Jar, Leyden?) 

The insulated handles H, H, Fig. 495, permit 




the balls at M, M, to be readily applied to the 
opposite coatings of the jar or condenser. 

The name discharging tongs is sometimes ap- 
plied to this apparatus. 

Rod, Lamp A metallic rod pro- 
vided in electric arc lamps for holding the 
carbon electrodes. 

When the upper carbon only is fed, as is the 
case in most arc lamps, there is usually but one 
lamp rod provided. The clutch or clamp of the 
feeding device acts against this rod, which must 
of necessity be at least as long as the upper carbon. 
(See Lamp, Arc, Electric.) 

Rod, Lightning — A rod, or wire 

cable of good conducting material, placed on 
the outside of a house or other structure, in 
order to protect it from the effects of a light- 
ning discharge. 

Lightning rods were invented by Franklin. 
The results of a very extended inquiry on the 
subject, leave no room for doubt that a lightning 
rod, properly placed and constructed, affords an 
efficient protection to the buildings on which 
it is placed. 

To insure this protection, however, the fol- 
lowing conditions were, until very recently, gen- 
erally insisted on in order to permit the rod to 
properly act, viz.: 

(1.) The rod, generally of iron or copper, 
should have such an area of cross- section as to 
enable it to carry without fusion the heaviest bolt 
it is liable to receive in the latitude in which it is 
located. 

When of iron, the area of cross-section should 
be about seven times greater than when of 
copper. 

(2.) The rod should be continuous throughout, 
all joints being carefully avoided. 

When joints are used, they should be made of as 
low resistance as possible, and should be pro- 
tected against corrosion. 

(3.) The upper extremity of the rod should 
terminate in one or more points formed of some 
metal that is not readily corroded, such as pla- 
tinum or nickel. 

(4.) The lower end of the rod should be car- 
ried down into the earth until it meets perma- 
nently damp or moist ground, where it should 
be attached to a fairly extended metallic surface 
buried in the ground. 

Metallic plates will answer for grounding the 



Rod.] 



463 



[Rod. 



rod, but, if gas or water pipes are available, the 
rod should be placed in good electrical connec- 
tion therewith, by wrapping it around and 
soldering it to such pipes. 

This fourth requirement is of great importance 
to the proper action of a lightning rod, and un- 
less thoroughly fulfilled, may render the rod 
worthless, no matter how carefully the other re- 
quirements are attended to. When a bolt strikes 
a lightning rod which is not properly grounded, 
the discharge is almost certain to destroy the 
building to which the rod is connected. 

(5.) The rod should not be insulated from the 
building, unless to prevent stains from the oxi- 
dation of the metal. On the contrary, the rod 
should be directly connected with all masses of 
metal in its path, such as tin roofs, gutter spouts, 
metallic cornices, etc. In this way only can dan- 
gerous disruptive lateral discharges from the rod 
to such masses of metal be avoided. 

(6.) The rod should project above the roof or 
highest part of the building, or, in other words, 
the height of the rod should bear a certain pro- 
portion to the size of the building to be pro- 
tected. 

A rod will protect a conical space around it, 
the radius of whose base is equal to the vertical 
height of the rod above the ground, but whose 
sides are curved inwards instead of being straight. 
Where the building is very high, a number of 
separate rods all connected to one another should 
be employed. 

A lightning rod sometimes fails to protect a 
house or barn, from the fact that a heated, ascend- 
ing current of air from a fire in the house, or 
from the gradual heating of green hay or grain in 
the barn, acting as a conductor, increases the vir- 
tual height of the house beyond the ability of its 
rods to protect it. 

(7.) A stranded conductor is much better than 
an equal cross-section of a solid rod of the same 
metal. 

A copper tape is better than a copper rod for 
lightning rods, because a rapidly periodic current, 
whose periodicity is sufficiently great, passes 
practically over the surface of the conductor only. 
Considering an electric current as taking its 
energy from the surrounding dielectric, a tape is 
better, because the surface which absorbs the 
energy is greater in the case of a tape than of a 
solid rod. (See Law, Poynting's.) 

A lightning rod more frequently acts to quietly 
discharge an impending cloud by convective dis- 



charge than by an actual disruptive discharge of 
the same. (See Discharge, Convective. Dis- 
charge, Disruptive.) 

Lightning rods should be frequently tested to 
see that no breaks or oxidation of their joints 
have occurred. 

Professor Lodge takes exception to some of the 
heretofore generally received notions concerning 
the action of lightning rods. He distinguishes 
between two distinct kinds of discharge that may 
occur between a charged cloud and the earth, 
viz. : 

(1.) A steady strain or current. 

(2. ) An impulsive rush or oscillatory discharge. 

A discharge by a steady strain or current oc- 
curs when the cloud gradually approaches a point 
on the earth; or, in the case of the cloud being 
stationary, when it receives its charge gradually 
by the approach of another cloud. 

In steady discharge, the lightning rod, with its 
pointed end, either quietly discharges the cloud 
by a convective discharge, or by a harmless con- 
ductive discharge through the rod, after a spark 
has passed disruptively between the cloud and 
the rod. (See Discharge, Convective. Dis- 
charge, Conductive. Discharge, Disruptive.) 

The impulsive discharge or rush occurs when- 
ever the cloud that discharges to the earth re- 
ceives its charge suddenly, as by the discharge 
into it of a neighboring cloud, or when a bound 
charge, produced by the presence of a neighbor- 
ing charged cloud, is suddenly liberated by dis- 
harge, and, thus becoming free, impulsively dis- 
charges to the earth. 

In all cases of an impulsive discharge or rush, a 
counter electromotive force is set up in the rod, 
which resists the discharge through the rod and 
causes the electricity to rush back and spit off in 
lateral discharges. In this case the conducting 
power of the rod has no effect in facilitating the 
discharge. Indeed, the smaller its resistance, and 
the longer the oscillations last, the greater the 
danger from lateral discharges. (See Discharge, 
Lateral. Path, Alternative.) 

The following principles advanced by Lodge 
differ from the views heretofore generally re- 
ceived, viz.: 

(1.) Iron is a better substance for a lightning 
rod than copper, because it is equally as good a 
conductor as copper for very rapidly alternating 
currents, and is more difficult to fuse. 

(2.) All neighboring metallic conductors should 
be connected to earth. These connections should. 



Rod.] 



464 



[Rot. 



preferably be by separate conductors rather than 
by the rod itself. 

(3.) The lightning conductors should have a 
good separate earth, but should be connected to 
water pipes, gas pipes, etc., if near them, by an 
underground connection. 

(4.) The lightning conductor should be de- 
tached from the building and not close against it. 

(5.) The rod should be of flat section, or a 
stranded conductor. 

Rod, Lightning, for Ships A 

system of rods designed to afford electric 
protection for vessels at sea. 

Since the lightning discharge takes place be- 
tween the points of greatest difference of poten- 
tial, and these points are generally the cloud 
and the nearest point of the earth, tall objects are 
especially liable to be struck. 

Ships at sea should, therefore, be thoroughly 
protected from lightning. 

In Harris' system of lightning protection for 
ships, the rods are connected with a series of 
copper plates and rods so placed on the masts as 
to readily yield to strains. These plates or rods 
are electrically connected with the copper sheath- 
ing of the vessel and with all large masses of 
metal in the vessel. This latter precaution is 
especially necessary in the case of men-of-war, 
in order to protect the powder magazine. 

Harris' method for the lightning protection of 
ships was adopted only after very considerable 
opposition. It proved, however, so efficacious in 
practice that serious effects of lightning on vessels 
so protected are now almost unknown. In 1845, 
Harris received the honor of knighthood from 
the English Government for his services m this 
respect. 

Rod, Lightning, Points on Points 

of inoxidizable material, placed on lightning 
rods, to effect the quiet discharge of a cloud by 
convection streams. (See Rod, Lightning, 
Convection, Electric?) 

Rod, Thunder ■ — A term formerly 

used for lightning rod. (See Rod, Light- 
ning.) 

Rods, Bus Heavy copper rods em- 
ployed in a central or distributing station, to 
which all the terminals of the generating dy- 
namos are connected, and from which the cur- 
rent passes to the different points of the dis- 
tribution system over the feeders. 



Bus rods are often called bus bars or bus wires. 
(See Wires, Bus.) 

Rodding a Conduit— (See Conduit, Rod- 
ding a.) 

Rolling Contact,— (See Contact, Rolling.) 

Rose, Ceiling An ornamental ceil- 
ing plate through which an electric conductor 
passes. 

Rosette. — An ornamental plate provided 
with contacts connected to the terminals of 
the service wires, and placed in a wall for the 
ready attachment of the incandescent lamp. 

A word sometimes used in place of rose. 

Rosette Cut-Out,— (See Cut-Out, Rosette?) 
Rotary Magnetic Polarization. — (See 

Polarization, Magnetic Rotary?) 

Rotary-Phase Current. — (See Current, 

Rotating?) 

Rotary-Phase Dynamo. — (See Dyjiamo, 
Rotary-Phase.) 

Rotary-Phase Motor. — (See Motor, Ro- 
tating Current?) 

Rotary-Phase Transformer. — (See Trans- 
foriner, Rotary-Phase?) 

Rotating Brushes of Dynamo-Electric 
Machine. — (See Brushes, Rotating, of 
Dyna mo-Electric Mach ines.) 

Rotating Current.— (See Current, Rota- 
ting?) 

Rotating Current Field.— (See Field, 
Rotating Current?) 

Rotating Current Motor 
Rotating Current?) 

Rotating Current 
Transfomier, Rotatory Current?) 

Rotation, Electro-Magnetic — A 

rotation obtained by electro-magnetic attrac- 
tions and repulsions. (See Disc, Arago's. 
Disc, Faraday's. Motor, Electric?) 

Rotation, Magneto-Optic A rota- 
tion of the plane of polarization of a beam 
of polarized light on its passage through a 
transparent medium when placed in a strong 
magnetic field. 

The medium only possesses such properties 
while in the field. 



(See Motor, 
Transformer. — (See 



Rub.] 



465 



[Sai. 



In a ray of ordinary light the vibrations of the 
ether particles are at right angles to the direction 
of the ray, or to the direction in which the light 
is moving. But the vibrations occur indiscrimi- 
nately in all planes passing through the line of 
direction. Under certain circumstances, all the 
ether particles may be caused to move in planes 
that are parallel to one another. Such a beam of 
light is called a plane polarized beam. 

A plane polarized beam of light, when passed 
through many transparent substances, will have 
its ether particles vibrating in the same plane 
when it emerges from the medium, as it had before 
it entered. Some transparent substances, how- 
ever, possess the property of rotating or turning 
the plane of polarization of the light to the right 

M N 




Fig. 4Q6. Magneto- Optic Rotation. 

or to the left. This property is called respec- 
tively right-handed rotary polarization, and left- 
handed rotary polarization. 

Many substances that ordinarily possess no 
power of rotary polarization acquire this power 
when placed in a magnetic field. This property 
of a magnetic field was discovered by Faraday. 



The effect is to be ascribed to the strain produced 
in the transparent medium by the stress of the 
magnetic field. It may be caused in solid bodies 
by mechanical force. 

The apparatus for demonstrating the rotation 
of the plane of polarization by a magnetic field is 
shown in Fig. 496. 

A powerful electro-magnet, M, M, is provided 
with a hollow core. The substance c, is placed 
in the field produced by the approached poles, 
and its action on the light of a lamp, placed at 
the end 1, is observed by suitable apparatus at a. 

Rubber of Electrical Machine. — A 

cushion of leather, covered with an electric 
amalgam, and employed to produce electricity 
by its friction against the plate or cylinder of 
a frictional electric machine. (See Machine, 
Frictional Electric?) 

Rubbing Contact.— (See Contact, Rub- 
bing.) 

Ruhmkorff Coil.— (See Coil, Ruhmkorff) 
RuhmkorfTs Commutator. — (See Com- 
mutator, Ruhmkorff 's) 
Rule, Ampere's, for Effect of Current on 

Needle A magnetic needle, when 

placed near a conductor through which a 
current is flowing, has its north pole deflected 
to the left of the observer, who is supposed 
to be swimming with the current and facing 
the needle. 



S. — A contraction employed for second. 

S. H. M. — A contraction employed for 
simple harmonic motion. 

S. N. Code. — A contraction for single needle 
code. 

S. W. 0. — A contraction for Standard Wire 
Gauge. 

Saddles, Telegraphic B rackets 

placed on the top of telegraphic poles for 
the support of the insulators. 

Saddle brackets are usually employed for the 
wire attached to the top of a telegraph pole. (See 
Pole, Telegraphic.) 



Safe Carrying Capacity of a Conductor. 

- (See Capacity, Safe Carrying, of a Con- 
ductor?) 
Safety Catch.— (See Catch, Safety) 
Safety Device for Multiple Circuits.— (See 
Device, Safety, for Multiple Circuits.) 
Safety Fuse.— (See Fuse, Safety) , 

Safety Lamp, Electric (See Lamp, 

Electric Safety) 

Safety Plug.— (See Plug, Safety) 
Safety Strip.— (See Strip, Safety) 
Saint Elmo's Fire.— (See Fire, St. El- 
mo's) 



Sal.] 



466 



[Sell, 



Salient Magnetic Pole. — (See Pole, Mag- 
netic, Salient?) 

Saline Creeping". — (See Creeping, Saline?) 

Salts, Electrolysis of The decom- 
position of a salt into its electro-positive and 
negative radicals or ions. (See Electrolysis?) 

Sandy Deposit, Electro-Metallurgical 

(See Deposit, Electro-Metalhirgical, 

Sandy?) 

Saturated Solution. — (See Solution, Sat- 
urated.) 

Saturation, Magnetic The max- 
imum magnetization which can be imparted 
to a magnetic substance. 

The condition of iron, or other paramag- 
netic substance, when its intensity of mag- 
netization is so great that it fails to be further 
sensibly magnetized by any magnetic force, 
however great. 

When the core of an electro-magnet is saturated 
by the passage of an electric current, the only 
further increase of its magnetization that is possi- 
ble, is that due to the magnetic field of the in- 
creased current which may be sent through its 
coils. This is comparatively insignificant. 

A permanent magnet is sometimes said to be 
super-saturated, that is, to have received more 
magnetism than it can retain for any considerable 
time after its magnetization. 

In the saturated field magnets of a dynamo-elec- 
tric machine the magnetic density is seldom taken 
at a larger value than 16,000 lines per square cen- 
timetre of area of cross-section. But this is only 
practical saturation, since Ewing has forced 
45,300 lines per square centimetre by using an 
enormously high magnetizing force (H == 24,500). 

Saturation, Magnetic, Diacritical Point 

of A term proposed by S. P. Thomp- 
son for such a value of the co-efficient of 
magnetic saturation, that the core is mag- 
netized to exactly one-half its possible max- 
imum of magnetization. 

Saw, Electric A platinized steel 

wire, employed while incandescent for cut- 
ting hard substance. 

Scale, Tangent A scale designed 

for use with a galvanometer, on which the 
values of the tangents are marked, instead of 



equal degrees as ordinarily, thus avoiding the 
necessity of finding from tables the tangents 
corresponding to the degrees. 

Such a scale may be constructed as follows: 
Draw the tangent B T, to the circle, Fig. 497, 
and lay off on it any number of equal divisions 
or parts, as, for example, the thirty shown in the 
annexed figure. Connect these parts with the 
centre C, of the circle. The arc of the circle will 




Fig 497. Tangent Scale. 
thus be divided into parts proportional to the 
value of the tangents of the angles. 

These parts are more nearly equal the nearer 
they are to B, and grow smaller and smaller the 
further they are from B. In tangent galva- 
nometers it is therefore very difficult to accurately 
determine the current strength when the deflec- 
tions of the needle are very large. 

Scale, Thermometer, Centigrade A 

thermometer scale, in which the length of the 
thermometric tube between the melting point 
of ice and the boiling point of water is divided 
into one hundred equal parts or degrees. 

Centigrade degrees are indicated by a C, thus 
O degree C. or 100 degrees C, to distinguish them 
from Fahrenheit degrees that are marked F. 
In the Fahrenheit scale the freezing point of 
water is taken at 32 degrees, and the boiling point 
at 212 degrees. 

Scale, Thermometer, Fahrenheit's 

— A thermometer scale in which the length 
of the thermometer tube between the melting 
point of ice and the boiling point of water is 
divided into 1 80 equal parts called degrees. 

Fahrenheit degrees are indicated by an F., 
thus, 32 degrees F. 

The freezing point of water in Fahrenheit's 
scale is marked 32 degrees F., and the boiling 
point of water is marked 212 degrees F. 

Schiseophone.— An electro-mechanical ap- 
pliance for detecting flaws and internal de- 
fects in rails or other metallic masses. 

The schiseophone consists essentially in the 
combination of a microphone and telephone with 
a mechanical hammer and induction balance. 



Sch. 



467 



[Scr. 



Sch weigher's Multiplier. — (See Multi- 
plier, Schweigger s) 

Scintillating Jar. — (See Jar, Scintillat- 
ing) 

Scratch Brush.— (See Brush, Scratch) 

Scratch Brush, Circular — (See 

Brush, Scratch, Circular) 

Scratch Brush, Hand (See Brush, 

Scratch, Hand) 

Scratch Brushing. — (See Brushing, 
Scratch) 

Screen, Electric A closed conduc- 
tor placed over a body to screen or protect it 
from the effects of external electrostatic fields. 

An electric screen is sometimes called an elec- 
tric shield. 

The ability of a closed, hollow conductor to act 
as a screen, arises from the fact that all points on 
its inner surface are at the same potential, and 
therefore are not affected by an increase or de- 
crease in the potential of the outside of the con- 
ductor as compared with that of the earth. (See 
Net, Faraday's.) 

No considerable thickness is required for the 
efficient operation of an electric screen. 

Screen, Magnetic A hollow box 

whose sides are made of thick iron, placed 
around a magnet or other body so as to cut 
it off or screen it from any magnetic field ex- 
ternal to the box. 

Magnetic screens are placed around delicate 
galvanometers to avoid any variations in their 
field due to extraneous masses of iron or neigh- 
boring magnets. They are also sometimes placed 
around watches to shield or screen the works 
from the effects of magnetism. 

To act effectively, when the external fields are 
at all powerful, magnetic screens must be made 
of thick iron. They differ in this respect from 
electrostatic shields, which will afford protection 
against electrostatic charges although they may 
be but mere films. 

Screen, Methven's A vertical rec- 
tangular metallic screen used in connection 
with a standard argand burner, for furnish- 
ing a standard amount of light for photo- 
metric purposes. 

In a rectangular screen a small vertical slot is 
made of such dimensions as to permit an amount 



of light to pass just equal to two standard candles. 
The proper burning of the argand lamp is de- 
termined by supplying sufficient gas to produce 
a flame exactly 3 inches high. The glass 
chimney used in the burner is 6 inches high, 
and is provided with two horizontal wires placed 
on each side of the burner at the required height. 

Methven's screen possesses the advantage of 
being easily used and of furnishing a reliable 
standard of light. Extended experiments made 
with it appear to show that the amount of light 
produced depends rather on the height of the 
gas flame than on the quality of the gas itself. 
In using Methven's screen care should be taken 

(1.) To see that the gas flame is of exactly the 
required height. 

(2.) That the chimney on the lamp is quite 
clean. 

(3.) That the top of the flame is as regular as 
possible. 

As this last point is almost impossible to obtain in 
actual practice, the flame is 
adjusted so that the highest 
point extends about one- 
eighth of an inch above the 
height of the horizontal 
wires. 

(4.) That the lamp and 
apparatus be permitted to 
acquire its normal temper- 
ature before the readings 
are taken. 

Fig. 498 shows the con- 
struction of the ordinary 
Methven standard screen. 
The vertical slot in the 
screen is placed as shown 
before the standard argand 
burner. Horizontal wires 
for the adjustment of the height of the flame are 
placed one on each side of the gas chimney. 

Screening, Electrostatic Screening 

or shielding from the inductive effects of a 
charge. 

A continuous metallic surface surrounding an 
air space to be shielded, completely protects any 
body placed within such air space from electro- 
static influence. (See Cube, Faraday's.) 

Screening, Magnetic Preventing 

magnetic induction from taking place by in- 
terposing a metallic plate, or a closed circuit 
of insulated wire, between the body producing 




Fig. 4Q8. Methven's 
Standard Screen. 



Scr.] 



468 



[Scr. 



the magnetic field and the body to be mag- 
netically screened. 

A magnetic needle is screened from the action 
of the earth's field by placing it inside a hollow 
iron box, which prevents the lines of force of the 
earth's field from passing through it by concen- 
trating them on itself. This action is dependent 
on the fact that iron is paramagnetic and there- 
fore offers the lines of force less resistance 
through its mass than elsewhere. A plate of 
copper would not effect any such magnetic 
shielding or screening. 

In any magnetic field, however, in which the 
strength of the field is undergoing rapid, periodic 
variations, a plate of copper or other electric 
conductor may act as a screen to protect neigh- 
boring conductors from the effects of magnetic 
induction, and its ability to thoroughly effect 
such a screening will depend directly on its 
conducting power. 

If, for example, the copper plate c (Fig. 499), 
be interposed between a coil of copper ribbon a, 
and the fine wire coil b, it will greatly reduce the 
intensity of the induced currents, produced when 
rapidly alternating currents are sent through a. 
If, however, the copper plate be slit, as shown to 
the right at a, the screening effect is lost, but is 
regained if the slit be connected by a conductor. 
Similarly a flat coil of insulated wire effects no 
screening action when open, but when closed acts 
as the uncut copper plate. 

Here the screening action is due to the fact 
that the energy of the field is spent in producing 
eddy currents in the interposed metal screen or 
coils. If the metal screen is discontinuous in the 
direction in which the eddy currents tend to flow, 
the inability of the screen to absorb the energy as 
eddy currents prevents its action as a screen. 




induction from occurring in a neighboring con- 
ductor, by interposing some conducting substance 
in which eddy currents can be freely established. 

As to the efficiency of the screening action, if the 
makes-and-breaks do not follow one another very 
rapidly, the following principles can be proved : 

(1.) If the screening material have absolutely 
no electrical resistance it will effect a perfect mag- 
netic screening when placed between the primary 
and secondary, no matter what its thickness 
may be. 

(2.) If the screen have a finite conductivity, 
the screening will be imperfect, unless the thick- 
ness of the material employed is considerable. 

If, however, the makes-and-breaks follow one 
another very rapidly, then 

The screening effect of even imperfect conduc- 
tors will become manifest with comparatively 
thin screens of metal. 

As to magnetic screening, therefore, it follows 
that the less the conductivity, the greater must 
be the speed of reversal, in order that the screen- 
ing action may be effective. 

Where a screen of iron is employed, an ad- 
ditional effect is produced by the fact that the 
small magnetic resistance of the metal, or its con- 
ductivity for lines of magnetic force, causes the 
lines of induction to pass through its mass, and 
thus effect a screening action for the space on the 
other side. This action is, by some, called mag- 
netic screening. 

In the case of iron screens, considerable thick- 
ness is required in the metal plate, in order to 
obtain efficient screening action of this latter 
character. On account of this action of iron, in 
conducting away lines of force, a much smaller 
speed of reversal is required, in order to obtain 
effective screening action, where plates of iron 
are used, than in the case of plates of other 
metal. 

The apparatus shown in Fig. 500 was employed 




Fig. 4Q 9. 

The word magnetic screening is generally em- 
ployed in the latter sense of preventing magnetic 



Fig. J 00. Willoughby Smith's Apparatus. 

by Mr. Willoughby Smith, in studying the effects 
of magnetic screening. 

The flat coils A, and B, were employed for the 
primary and secondary coils respectively, and 
were connected to the battery C, and the galva- 



Scr.] 



469 



[Sec. 



nometer F, as shown. Current reversers, D and 
E, were so arranged as to reverse galvanometer 
and battery alternately, and so cause the oppo- 
site induced currents to affect the galvanometer in 
the same direction. If the commutators were 
caused to reverse the current slowly, a plate of 
copper interposed between A and B, produced 
but little effect on the galvanometer, but if the re- 
versers were driven at a very rapid rate, a marked 
decrease of deflection occurred. 

The screening action of the metals, or their 
ability to diminish the galvanometer deflection, 
is in the order of their electrical conductivity, ex- 
cept in the case of iron, which, as we have seen 
already, has an additional screening power, due 
to its conducting away the lines of magnetic force. 

It follows from the preceding principles that 
the use of lead covered cables, for the conveyance 
of periodic currents, of the frequency of, say, sixty 
to one hundred alternations per second, is of but 
little or no advantage for protecting neighboring 
telephones from inductive action, because 

(i.) Lead is a poor conductor. 

(2.) The rapidity of alternation is too slow. 

J. J. Thomson made some experiments with 
electrical oscillations produced by resonance, of 
about io^ in frequency. He obtained this fre- 
quency of oscillation from oscillations set up in 
the primary of an induction coil, in a secondary 
circuit of suitable dimensions. The presence of 
these secondary vibrations or waves was shown 
by means of the sparks seen at the terminals of a 
spark-micrometer circuit. Under these circum- 
stances he found that the interposition of a thin 
sheet of tin foil or gold leaf at once completely 
stopped the secondary sparks by the shielding 
action it exerted. 



-Screen- 



Screening, Magnetostatic — 

ing from the inductive effect of a stationary 
magnetic field. 

Magnetostatic screening differs from electrostatic 
screening in that the plate of iron or other para- 
magnetic material surrounding the space to be 
screened must have a fairly considerable thick- 
ness. This arises from the fact that the magnetic 
susceptibility of the substance is not infinitely 
great. 

Screw, Binding A name some- 
times applied to a binding post. (See Post, 
Binding.) 

Seal, Hermetical Such a sealing of 



a vessel, designed to hold a vacuum, or gas- 
eous atmosphere under pressures greater or 
less than that of the atmosphere, as will pre- 
vent either the entrance of the external at- 
mosphere into the vessel, or the escape of the 
contained gas into the atmosphere. 

Hermetical sealing may be accomplished either 
by the use of suitable cements, or by the direct 
fusion of the walls of the containing vessel. The 
latter method is generally employed. 

Search Light, Automatic —(See 

Light, Search, Automatic?) 

Search Light, Electric (See Light, 

Search, Electric?) 

Secohm. — The practical unit of self-induc- 
tion, or the practical unit of inductance, 

The secohm is equivalent to a length equal to 
that of an earth quadrant, or io* centimetres. 

The word secohm is a contraction for second, 
ohm, and implies the fact that the product of the 
ohm and the second are taken. 

The word henry is now generally used in the 
United States for secohm. (See Henry.) 

Secohmmeter. — An apparatus for measur- 
ing the co-efficient of self-induction, mutual 
induction and capacity of conductors. (See 
Secohm. Lnduction, Mutual. Induction, 
Self.) 

The principle of the secohmmeter depends 
upon successively performing the cycle of magnetic 
operations, by making and breaking the circuit 
of a galvanometer by means of a commutator 
capable of working at a definite speed. 

Second, Ampere One ampere flow- 
ing for one second. (See Hour, Ampere.) 

Second, Watt A unit of electricaL 

work. 

A watt -second equals the work due to the ex- 
penditure of an electrical power of one watt for 
one second. It is the same as a volt-coulomb. 

The watt-second and the H. P. hour, etc., 

Work 



are units of work, since Power = 



Time 



therefore, power X time = work. 

Secondary Battery. — (See Battery, Sec- 
ondary.) 

Secondary Battery, Cell of —(See 

Cell, Secondary.) 



Sec] 



470 



[Sec. 



Secondary Cell. — (See Cell, Secondary?) 

Secondary Cell, Jar of (See far of 

Secondary Cell) 

Secondary Clock. — (See Clock, Second- 
ary) 

Secondary Coil. — (See Coil, Secondary.) 

Secondary Currents. — (See Currents, 
Secondary) 

Secondary, Fixed The secondary 

of an induction coil, that, as is common in 
such coils, is fixed, as contradistinguished 
from a movable secondary. (See Secondary, 
Movable) 

Secondary Generator. — (See Generator, 
Secondary) 

Secondary Impressed Electromotive 
Force. — (See Force, Electromotive, Second- 
ary Impressed) 

Secondary, Movable The second- 
ary conductor of an induction coil, which, in- 
stead of being fixed as in most coils, is mova- 
ble. 

The peculiar movements observed in the 
secondary of an induction coil when the second- 
ary is free to move, have been carefully studied 
by Prof. Elihu Thomson. The secondaries 
employed for this purpose are in the shape of 
rings, discs, spheres, wedges, bars, wheels, etc., 
etc. 

The primary is in the form of a straight cylin- 
drical coil surrounding a straight core. The coils 
are traversed by rapidly alternating currents and 
possess considerable impedance. 

Among the many phenomena concerning the 
behavior of movable secondaries in such a rapidly 
alternating field are the following, viz.: 

(i.) A metallic ring, resting on lugs attached 
to the coils of the primary, is thrown violently off 
the magnet on the passage of alternating currents 
through the primary. 

(2.) Two metallic rings of the same diameter 
brought into the field are mutually attracted to 
each other, with sufficient force to sustain the 
weight of one of the rings when the other ring is 
held in the field. 

(3.) Metallic spheres are set into rotation when 
so held near the primary pole as to be shielded 



from the action of part of the rapidly alternating 
field. When held on one side of the pole, this 
rotation occurs in the opposite direction to that 
when held on the opposite side. 

(4.) Metallic discs similarly placed are simi- 
larly set into rotation. 

(5.) The speed of rotation of spheres or discs 
varies in different positions. 

(6.) Spheres or discs of diamagnetic substances 
attain their maximum rotation when held in posi- 
tion at right angles to those of paramagnetic sub- 
stances. 

(7.) Bars of steel or substances possessing high 
coercive power, placed dissymmetrically on the 
primary as regards their centres of gravity, ex- 
hibit the phenomena of a shifting magnetic field. 
(See Field, Magnetic, Shifting.) 

(8.) A wedge-shaped piece of steel placed with 
a flat face on the primary, exhibits a shifting 
magnetic field, and acts on movable metallic 
masses near it, just as though a fluid substance 
was escaping with great velocity from its edges. 

Secondary Movers. — (See Movers, Second- 
ary) 

Secondary Plate of Condenser.— (See 

Plate, Secondary, of Condenser) 

Secondary Spiral. — (See Spiral, Second- 
ary) 

Secretion Current— (See Current, Secre- 
tion) 

Section Line of Electric Railway.— (See 

Railroads, Electric, Section Line of) 

Section, Neutral, of Magnet — A 

section passing through the neutral line or 
equator of a magnet. (See Line, Neutral, 
of a Magnet. Magnet, Equator of) 

Section, Trolley A single contin- 
uous length of trolley wire, with or without 
its branches. 

Sectional or Divided Overhead System 
of Motive Power for Electric Railroads. — 

(See Railroads, Electric, Sectional Over- 
head Sy stein of Motive Power for) 

Sectional or Divided Surface System of 
Motive Power for Electric Railroads. — 

(See Railroads, Electric, Sectional Surf ace 
System of Motive Power for) 



Sec] 



471 



[Sep. 



Sectional or Divided Underground 
System of Motive Power for Electric Rail- 
roads. — (See Railroads, Electric, Sectional 
Underground System of Motive Power for.) 

Sectional Plating. — (See Plating, Sec- 
tional.) 

Sectional Plating Frame. — (See Frames, 
Sectional Plating?) 

Seebeck Effect— (See Effect, Seebeck.) 

Seismograph, Electric An appa- 
ratus for electrically recording the direction 
and intensity of earthquake shocks. 

Seismograph, Micro An electric 

apparatus for photographically registering 
the vibrations of the earth produced by earth- 
quakes or other causes. 

The micro-seismograph consists essentially of a 
microphone placed on the ground and connected 
with a telephone. A small concave mirror mova- 
ble about a horizontal axis is supported on a 
plate of aluminium supported on a platinum wire 
connected with the diaphragm of the telephone. 
The movements of the diaphragm of the telephone 
are permanently recorded on a strip of sensitized 
paper that is moved before the mirror. 

Selective Absorption. — (See Absorption, 
Selective.) 

Selenium. — A comparatively rare element 
generally found associated with sulphur. 

Selenium Battery.— (See Battery, Selen- 
ium?) 

Selenium Cell. — (See Cell, Selenium) 

Selenium Eye. — (See Eye, Selenium?) 

Selenium Photometer. — (See Photometer, 
Selenium?) 

Self-Induced Current.— (See Currents, 
Self-Induced?) 

Self-Induction. — (See Induction, Self.) 

Self-induction, Co-efficient of (See 

Induction, Self Co-efficient tf.) 

Self-Recording Magnetometer.— (S e e 
Magnetometer, Self -Re cor ding?) 

Self-Registering Wire Gauge. — (See 
Gauge, Wire, Self-Registering?) 

Self-Winding Clock.— (See Clock, Self- 
winding.) 



Semaphore. — A variety of signal apparatus 
employed in railroad block systems. 

The semaphore used on the Pennsylvania Rail- 
road consists of a wooden post, in the neighbor- 
hood of twenty feet in height, on which a wooden 
arm or blade, six feet in length and a foot in 
width, is displayed. 

When the block is clear, during the day the 
arm is placed pointing downwards at an angle of 
75 degrees with the horizontal ; during night 
semaphore displays a white light. When the 
block is not clear, the arm or blade is placed in a 
horizontal position by day, or displays a red light 
at night. (See Railroads, Block System for.) 

Semaphore Arm. — (See Arm, Semaphore?) 

Semaphore Indicator. — (See Indicator, 
Seinaphore?) 

Sender, Zinc A device employed 

in telegraphic circuits, by means of which, in 
order to counteract the retardation produced 
by the charge given to the line, a momen- 
tary reverse current is sent into the line after 
each signal. 

A zinc sender generally consists of a low resist- 
ance Siemens relay introduced between the line 
and the front contact of the signaling key. 

Sensibility, Electro An effect pro- 
duced on a sensory nerve by its electrization. 

Sensibility of Galvanometer. — (See Gal- 
vanometer, Sensibility of.) 

Sensitive Thread Discharge. — (See Dis- 
charge, Sensitive Thread?) 

Separate Coil Dynamo-Electro Machine. 
— (See Machine, Dynamo-Electric, Separate 
Coil?) 

Separate Touch, Magnetization by 

— (See Touch, Separate?) 

Separately Excited Dynamo.— (See Dy- 
namo, Separately Excited) 

Separately Excited Dynamo-Electric 
Machine. — (See Machine, Dynamo-Electric, 
Separately Excited?) 

Separator. — An insulating sheet of ebonite, 
or other similar substance, corrugated and 
perforated so as to conform to the outline of 
the plates of a storage battery, and placed 
between them at suitable intervals, in such a 



Ser.] 472 [Ser.. 

manner as to avoid short-circuiting, without The difference in potential between zinc and 

impeding the free circulation of the liquid. carbon is equal to 1.089, and is obtained by add- 

Series and Magneto Dynamo-Electric ^^^^^^^^^^^^ 

Machine. — (See Machine, Dynamo-Electric, p ' 

Series and Magneto) ' 2I ° + ' o6 9 +'W + - 1 * 6 + *& +-»3 =1.089. 

Series and Separately Excited Dynamo- This fact is known technically as Volttfs Law, 

Electric Machine.-(See Machine, Dynamo- which ma y be formulated as follows: 

Electric, Series and Separately Excited) The difference of potential, produced by the con- 

tact of any two metals, is equal to the sum of the 

Series and Shunt-Wound Dynamo-Elec- differences f potentials between the intervening 

trie Machine.— (See Machine, Dynamo- me tals in the contact series. 

Electric, Series and Shunt-Wound) Serieg Bistrilbntion of Electricity by 

Series Vircuit.-(See Circuit Series) ^ mXsaA Currents.- (See Electricity, Se- 

Series-Connected Battery.- (See i?*//^, ^ Distribution ofy by Constant Currenf 

Series-Connected) ~. ... 

Series-Connected Electro-Receptive De- 'series-Mnltiple.-A series of multiple 

vices. — (See Devices, Electro-Receptive, Se- .. /c . ^. ., a • ** 7* -j.r \ 

_ v 7 N r > connections. (See Circuit, Series-Multiple) 
ries-Connected.) 

Series-Connected Electro-Receptive De- Series-Multiple Circuit— (See Circuit, 

vices, Automatic Cut-out for (See Series-Multiple) 

Cut-out, Automatic, for Series-Connected Series - Multiple-Connected Electro-Re- 

Electro-Receptive Devices) ceptive Devices.— (See Devices, Electro-Re- 

Series-Connected Sources.-(See Sources, ce ^ tive > Series-Multiple-Connected) 

Series-Connected) Series-Multiple-Connected Sources. — 

Series-Connected Translating- Devices. ( See Sources, Series-Multiple-Connected) 

— (See Devices, Translating, Series-Con- Series-Multiple-Connected Translating 1 

nected) Devices. — (See Devices, Translating, Series- 

Series-Connected Toltaic Cells. — (See Multiple-Connected) 

Cells, Voltaic, Series-Connected) Series-Multiple Connection.— (See Con- 

Series Connection.— (See Connection, nection, Series-Multiple) 
Series) Series, Parallel A term some- 
Series, Contact A series of metals times applied to a multiple-series connection. 

arranged in such an order that each becomes (See Connection, Multiple-Series) 

positively electrified by contact with the one ^^ Therni O-Electric A list of 

a o ows 1 . metals so arranged according to their ther- 

The contact values of some metals, according , L . . . , , , A , . ,, 

. , _ M , ' & mo-electric powers, that each metal in the 

to Ayrton and Perry, are as follows: , 

series is electro-positive to any metal lower m 

CONTACT SERIES. the list 

Difference of Potential in Volts. Series-Transformer.— (See Transformer, 

Zinc I Series) 

Lead f " Series Turns of Dynamo-Electric Ma- 

T ^ j- 069 chine. — (See Turns, Series, of Dynamo- 

rpj n 1 Electric Machine) 

Iron j 3 J 3 Series Winding 1 . — (See Winding, Series.) 

* ron I Tyf fi Series- Wound Dynamo.— (See Dynamo y 

£ PP e e r r 4 Series.) 

Platinum ... ... f 2 3 8 Series-Wound Dynamo-Electric Machine. 

Platinum j — (See Machine, Dynamo-Electric, Series- 

Carbon j" lI 3 Wound) 



Ser.] 



473 



[She. 



Series-Wound Motor. — (See Motor, Se- 
ries- Wound?) 

Service Conductors.— (See Conductors, 
Service.) 



Service, Street 



•In a system of in- 



candescent lamp distribution that portion of 
the circuit which is included between the 
main and the service cut-out. 



Cable 



-The covering 1 of 



Serving, 

hemp or jute spun around the insulated core 
of a cable to act as a protection against the 
pressure of the iron wire which forms the 
armor of the cable. 

Shackling" a Wire. — Inserting an insula- 
tion between the two ends of a cut wire. 

Shaded or Screened. — Cut off or screened 
from the effects of an electrostatic or mag- 
netic field. (See Screening, Magnetic. Screen, 
Magnetic. Screen, Electric?) 

Shadow, Electric A term some- 
times used for molecular shadow. (See 
Shadow, Molecular?) 

Shadow, Molecular The compara- 
tively dark space on those parts of the walls 
of Crook'es' tubes, which have been protected 
from molecular bombardment by suitably 
placed screens. 




Fig- 501. Molecular Shadow. 

If a, in the Crookes tube, shown in Fig. 501, 
be connected with the negative pole of an elec- 
tric source, and the cross-shaped mass of alu- 
minium at b, be connected with the positive elec- 
trode, on the passage of a series of rapid 
discharges, phosphorescence is produced by the 
molecular bombardment from a, in all parts of 
the vessel opposite a, except those lying in the 



projection of its geometrical shadow. (See Phos- 
phorescence, Electric. ) 

Shadow Photometer.— (See Photometer, 
Shadow?) 

Shaft, Driven A shaft which re- 
ceives its power from the driving shaft. (See 
Mover, Prime?) 

Shaft, Driving" The main line of 

shafting which takes its power directly from 
the prime mover. 

Shallow- Water Submarine Cable.— (See 

Cable, Submarine, Shallow- Water?) 

Sheath, Protective A device at- 
tached to a transformer or converter, to pre- 
vent any connection from taking place between 
the high-potential primary circuit and the 
low-potential secondary circuit. 

The protective sheath devised by Prof. Ehhu 
Thomson consists essentially in an earth-con- 
nected copper strip or divided plate interposed 
between the windings for the secondary and pri- 
mary circuit. Should the primary circuit lose its 
high insulation it becomes grounded. 

Sheet, Current — The sheet into 

which a current spreads when the wires of 

any source are connected at any two points 
near the middle of a very large and thin con- 
ductor. 

A continuous electric current does not flow 
through the entire mass of a conductor in any 
single line of direction. If the terminals of any 
source are connected to neighboring parts of a 
greatly extended thin conductor, the current 
spreads out in a thin sheet known as a cur- 
rent sheet, and instead of flowing in a straight 
line between the points, spreads over the plate 
in curved lines of flow, which, so far as shape is 
concerned, are not unlike the lines of magnetic 
force. 

Sheet Lightning". — (See Lightning, 
Sheet?) 

Shellac. — A resinous substance possessing 
valuable insulating properties, which is ex- 
uded from the roots and branches of certain 
tropical plants. 

The specific inductive capacity of shellac as 
compared with air is 2.74. 



She.] 



474 



[Shu. 



Shell, Magnetic 



-A sheet or layer 



consisting of magnetic particles, all of whose 
north poles are situated in one of the flat 
surfaces of the layer, and the south poles in 
the opposite surface. (See Magnetism, La- 
mellar Distribution of) 

Shell Transformer. — (See Transformer, 
Shell) 

Shield, Magnetic, for Watches A 

hollow case of iron, in which a watch is per- 
manently kept, in order to shield it from the 
influence of external magnetic fields. (See 
Screen, Magnetic.) 

Shifting Magnetic Field.— (See Field, 
Magnetic, Shifting.) 

Shifting Zero. — (See Zero, Shifting.) 

Ships, Lightning Rods for (See 

Rod, Lightning, for Ships.) 

Ship's Sheathing, Electric Protection of 

-Attaching pieces of zinc to the copper 



sheathing of a ship for the purpose of prevent- 
ing the corrosion of the copper by the water. 
(See Metals, Electrical Protectioji of.) 



Shock, Break 



-A term sometimes 



employed in electro-therapeutics for the 
physiological shock produced on the opening 
or breaking of an electric circuit. 

Shock, Electric The physiological 

shock produced in an animal by an electric 
discharge. 

Shock, Opening The physiological 

shock produced on the opening or breaking 
of an electric circuit. 



Shock, Static 



-A term employed in 



electro-therapeutics for a mode of applying 
Franklinic currents or discharges, by placing 
the patient on an insulating stool and apply- 
ing one pole of a static machine provided 
with small condensers or Leyden jars, to an 
insulated platform on which the patient is 
placed, while the other pole is applied to the 
body of the patient by the operator. 

The electrode applied to the body of the pa- 
tient is provided with a ball electrode. Shocks 
are given to the patient on the approach of 
this electrode by the discharge of the Leyden 
jars. 



Short- Arc System of Electric Lighting. 

— (See Lighting, Electric, Short-Arc Sys- 
tem.) * 

Short-Circuit.— To establish a short cir- 
cuit. (See Circuit, Short) 

Short-Circuit Key.— (See Key, Short- 
Circuit.) 

Short-Circuiting. — Establishing a short 
circuit. (See Circuit, Short.) 

Short- Circuiting Plug. — (See Plug, 
Short-Circuiting.) 

Short-Coil Magnet— (See Magnet, Short- 
Coil.) 

Short-Core Electro-Magnet. — (See Mag- 
net, Electro, Short-Core.) 

Short-Shunt Compound-Wound Dyna- 
mo-Electric Machine. — (See Machine, Dy- 
namo-Electric, Compound- Wound, Short- 
Shunt) 

Shunt. — An additional path established 
for the passage of an electric current or dis- 
charge. 

Shunt. — To establish an additional path 
for the passage of an electric current or dis- 
charge. 

Shunt and Separately Excited Dynamo- 
Electric Machine.— (See Machine, Dynamo- 
Electric, Shunt and Separately Excited) 

Shunt Circuit. — (See Circuit, Shunt) 

Shunt Dynamo-Electric Machine. — (See 
Machine. Dynamo-Electric , Shunt- Wound) 

Shunt, Electric Bell (See Bell, 

Shunt, Electric) 

Shunt, Electro-Magnetic In a sys- 
tem of telegraphic communication an electro- 
magnet whose coils are placed in a shunt 
circuit around the terminals of the receiving 
relay. 

The electro -magnetic shunt operates by its 
self-induction. Its poles are permanently closed 
by a soft iron armature so as to reduce the resist- 
ance of the magnetic circuit. (See Induction?. 
Self.) 



Shu.] 



475 



[Shu. 



On making the circuit in the coils of a receiv- 
ing relay, a current is produced in the coils of the 
electro- magnetic shunt in the opposite direction 
to the relay current; and, on breaking the circuit 
in the relay, a current is produced in the coils of 
the electro-magnetic shunt in the same direction 
as the current in the relay. 

The connection of the coils of the electro-mag- 
netic shunt with those of the receiving relay, how- 
ever, is such that on making the circuit in the 
relay the current in the shunt coils flows through 
the relay in the same direction, and on breaking 
the circuit it flows in the opposite direction. 
Therefore this shunt produces the following effects : 

(i.) At the commencement of each signal in 
the receiving relay, it produees an induced cur- 
rent in the same direction which strengthens the 
current in the relay. 

(2.) At the ending of each signal in the receiv- 
ing relay, it produces a current in the opposite 
direction, which hastens the motion of the tongue 
of the polarized relay. (See Relay, Polarized.) 

Shunt, Galvanometer A shunt 

placed around a sensitive galvanometer for 
the purpose of protecting it from the effects 
of a strong current, or for altering its sensi- 
bility. (See Shunt^) 

The current which will flow through the shunt 
wire depends on the relative resistance of the gal- 
vanometer and of the shunt. In order that only 



To> t£o> or ToV 0> of the 
total current shall pass 
through the galvanome- 
ter, it is necessary that 
the resistances of the 
shunt shall be the \, ^, 
or ^i- ¥ , of the galvanom- 
eter resistance. 

Fig. 502 shows 
shunt, in which the re- 
sistances, as compared 
with that of the galva- 
nometer, are those above 
referred to. The galva- 
nometer terminals are 
connected at N, N. Plug 
keys are used to connect one or another of the 
shunts with the circuit. (See Shunt, Multiplying 
Power of.) 

Shunt, Magnetic An additional 

path of magnetic material provided in a mag- 




Fig. 502. Galvanometer 
Shunt. 



netic circuit for the passage of the lines of 
force. 
Shunt, Multiplying Power of A 

quantity, by which the current flowing through 
a galvanometer provided with a shunt, must 
be multiplied, in order to give the total cur- 
rent. 

The multiplying power of a shunt may be de- 
termined from the following formula, viz.: 

A=r (^-^) X C, in which ^-ti = the mul- 
tiplying power of a shunt whose resistance is s; 
g, is the galvanometer resistance; C, the current 
through the galvanometer, and A, the total cur- 
rent passing; s and g, are taken in ohms, and C 
and A, in amperes. 

Suppose, for example, that but ^ the entire 
current is to flow through the galvanometer; then 
the resistance of the shunt must evidently be \ g, 
for, 

s 1 _ 1 

s 4- g — l + 9 "~ io' 
or, 10 s = s -f- g. 10 s — s=g .-. 9 s=g; or, 

s = (i)g- 

Shunt or Reducteur for Ammeter. — (See 

Reducteur or Shunt for Ammeter?) 

Shunt Ratio. — The ratio existing between 
the shunt and the circuit which it shunts 
(See Shunt, Multiplying Power of.) 

Shunt, Relay, Stearns' — A shunt 

employed in the differential method of duplex 
telegraphy to short-circuit the relay and then 
permit the line current to be cut off directly 
after it has completed its work in closing the 
local circuit. 

The use of the relay shunt permits the slacken- 
ing of the armature spring of the relay, because 
the decreased duration of the line current does 
not produce so strong a magnetization of the 
iron. 

Shunt-Turns of Dynamo-Electric Ma- 
chine. — (See Turns, Shunt, of Dynamo- 
Electric Machine.) 

Shunt-W-ound Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric ; 
Shunt- Wound.) 

Shunt- Wound Motor. — (See Motor ; 
Shunt- Wound.) 



Shu.] 



476 



[Sig. 



Shunting. — Establishing a shunt circuit. 

Shuttle Armature. — (See Armature, 
Shuttled) 

Side A, of Quadruplex Table. — (See Table, 
Quadruplex, A, Side of.) 

Side B, of Quadruplex Table.— (See Table, 
Quadruplex, B, Side of.) 

Side Flash. — (See Flask, Side.) 

Sidero-Magnetic. — (See Magnetic, Side- 
ro.) 

Siemens' - Armature Electro-Magnetic 
Bell. — (See Bell, Electro-Magnetic, Siemens 
Armature For?n) 

Siemens' Differential Voltameter, — (See 
Voltameter Sie?nens' Differential.) 

Siemens' Electric Pyrometer. — (See Py- 
rometer, Siemens' Electric?) 

Siemens-Halske Yoltaic Cell. — (See Cell, 
Voltaic, Siemens-Halske?) 

Siemens' Water Pyrometer. — (See Py- 
rometer, Siemens' Water.) 

Signal Arm.— (See Arm, Signal.) 

Signal, Electric Tell-Tale An 

electrically operated signal, generally silent, 
whereby the appearance of a white or colored 
disc, on a black or otherwise uniformly 
colored surface, indicates the occurrence of 
a certain predetermined event. 

Signal Service for Electric Railways.— 
(See Railroads, Electric, Signal Service 
System for.) 

Signals, Electro-Pneumatic —Sig- 
nals operated by the movements of dia- 
phragms or pistons moved by compressed 
air, the escape of which is controlled electri- 
cally. 

Signaling, Balloon, for Military Pur- 
poses • Transmitting intelligence of the 

movements of an enemy's army obtained from 
observations made in balloons by means of tel- 
ephone circuits connected with the balloon. 

Signaling, Curb —In cable teleg- 
raphy a system for avoiding the effects of 
retardation by rapidly discharging the cable 
before another electric impulse is sent into 



it, by reversing the battery, before connecting 
it to earth, and then connecting to earth be- 
fore beginning the next signal. 

Signaling, Double-Curb In curb 

signaling, a method by which the cable, after 
being connected with the battery for sending 
a signal, is subjected to a reverse battery, but 
instead of being put to earth after this con- 
nection, as in single-curb signaling, the bat- 
tery is again reversed and connected to earth. 

The time during which the cable is connected 
to the reversed battery before being put to earth, 
that is, the time during which it receives the 
positive and negative currents, may be made of 
any suitable duration. 

Signaling, Double-Current Signal- 
ing by means of currents that alternately 
change their direction, 

Double-current signaling was devised by Var- 
ley in order to avoid the effects of the induction 
of underground conductors on Morse tele- 
graphic apparatus. The idea of reversing the 
direction of the current was to hasten the dis- 
charge of the wire, which was prolonged by in- 
duction. Double- current working, however, 
possesses other advantages, and is used in duplex 
and quadruplex transmission. 

Signaling, Single-Curb — In curb 

signaling, a method by which the cable, after 
connection with the battery for sending a 
signal, is subjected to a reverse battery cur- 
rent, and then put to earth before again being 
connected to the battery for sending the next 
signal. 

Signaling, Single-Current Signal- 
ing by making or breaking the circuit of a 
single current. 

Single-current signaling is of two kinds, viz. : 

(i.) Open-Circuit Signaling, in which the bat- 
teries are fixed at each station, and are in circuit 
only when signaling. 

(2.) Closed-Circuit Signaling, where the bat- 
teries are divided, one half generally being at each 
end of the line, and so connected that both sets 
flow in the same direction. 

Signaling, Single-Current, Closed-Circuit 

A system of single-circuit signaling in 

which the sending batteries are placed at 
each end of the line and are so connected as 



Sig.l 



477 



[Sin, 



to remain always in circuit. (See Signaling, 
Single- Curre?it.) 
Signaling, Single-Current, Open-Circuit 

A system of single-current signaling 

in which the sending batteries, fixed at each 
station, are in circuit during signaling only. 
(See Signaling, Single-Current) 

Signaling, Velocity of Transmission of 

The speed or rate at which successive 

signals can be sent on any line without the 
retardation producing serious interference. 
(See Retardation) 

Silent Discharge. — (See Discharge, Si- 
lent.) 
Silver Bath.— (See Bath, Silver.) 

Silver Chloride Toltaic Cell.— (See Cell, 
Voltaic, Silver Chloride) 

Silver Plating. — (See Plating, Silver) 

Silver Toltameter. — (See Voltameter, 
Silver^) 

Silvered Plumbago. — (See Plumbago, Sil- 
vered?) 

Silvering, Electro Covering a sur- 
face with a coating of silver by electro-plat- 
ing. (See Platijig, Electro?) 

Electro-plating with silver. 

Silurus Electricus. — The electric eel. 
(See Eel, Electric?) 

Simple Arc. — (See Arc, Simple?) 

Simple Circuit. — (See Circuit, Simple?) 

Simple Electric Candle-Burner.— (See 
Burner, Simple Candle Electric?) 

Simple-Harmonic Current. — (See Cur- 
rent, Simple-Harmonic?) 

Simple-Harmonic Curve. — (See Curve, 
Simple-Harmonic?) 

Simple-Harmonic Motion. — (See Motion, 
Simple-Harjnonic) 

Simple Magnet. — (See Mag?iet, Szmple) 

Simple-Periodic Current. — (See Cur- 
rents, Sijnple-Per iodic) 

Simple-Periodic Electromotive Force. 
—(See Force, Electromotive, Simple- 
Periodic) 



Simple-Periodic Motion.— (See Motion, 
Simple-Periodic?) 

Simple Radical. — (See Radical, Simple?) 

Simple-Sine Motion. — (See Motion, 
Si7nple-Sine.) 

Simple Toltaic Cell.— (See Cell, Voltaic, 
Simple?) 

Simplex Telegraphy. — (See Telegraphy, 
Simplex?) 

Sims-Edison Torpedo. — (See Torpedo, 
Sims-Edison?) 

Sine Galvanometer. — (See Galvanometer, 
Sine?) 

Single-Brush Rocker. — (See Rocker, 
Single-Brush ) 

Single-Cup Insulator. — (See Insulator, 
Single- Shed?) 
Single Curh. — (See Curb, Single?) 

Single-Current Signaling. — (See Signal- 
ing, Single-Current.) 

Single-Curve Trolley Hanger. — (See 
Hanger, Single-Curve Trolley?) 

Single-Fluid Hypothesis of Electricity. 

— (See Electricity, Si7igle-Fluid Hypothesis 
of.) 

Single-Fluid Toltaic Cell.— (See Cell, 
Voltaic, Single-Fluid?) 

Single-Loop Armature. — (See Armature, 
Single-Loop.) 

Single-Magnet Dynamo-Electric Ma- 
chine.— (See Machine, Dynamo-Electric, 
Single-Magnet.) 

Single-Pair Yoke. — (See Yoke, Single- 
Pair.) 

Single-Shackle Insulator. — (See Insula- 
tor, Single-Shackle?) 

Single-Shed Insulator. — (See Insulator, 
Single-Shed.) 

Single-Stroke Electric Bell.— (See Bell, 
Single- Stroke Electric) 

Single Touch. — (See Touch, Single) 

Single-Wire Cable. — (See Cable, Single- 
Wire) 



Sin.] 



478 



[Sme. 



Single-Wire Circuit. — (See Circuit, 
Single- Wire.) 

Sinistrorsal Solenoid or Helix. — (See So- 
lenoid, Sinistrorsal.) 

Sinuous Currents. — (See Current, Sinu- 
ous^) 

Siphon, Electric — A siphon in 

which the stoppage of flow, due to the 
gradual accumulation of air, is prevented by 
electrical means. 

In the electric siphon, an opening is provided 
at the highest part of the bend of the siphon tube, 
and a chamber is attached thereto, provided with 
a float. Contact points are so connected with the 
float that when it falls, contact is made, and when 
it rises, contact is broken. 

The closing of the circuit, on the fall of the 
float, operates an electric motor which drives an 
air pump which exhausts the air from the siphon. 
Or the float being raised in the siphon, the con- 
tact is broken and the operation of the pump is 
stopped. 

Siphon Recorder. — (See Recorder, Si- 
phon.) 

Sir William Thomson's Standard Cell. — 

(See Cell, Voltaic, Standard, Sir William 
Thomson's.) 

Skin Effect.— (See Effect, Skin.) 

Skin, Faradization of The thera- 
peutic treatment of the skin by a faradic cur- 
rent. 

For efficient faradization the skin should be 
thoroughly dried and a metallic brush or elec- 
trode employed. For very sensitive parts, as, 
for example, the face, the hand of the operator, 
first thoroughly dried, is to be preferred as an 
electrode. 

Skin, Human, Electric Resistance of 

— The electric resistance offered by the 
skin of the human body. 

The electric resistance of the skin is subject to 
marked differences in different parts of the body, 
where its thickness or continuity varies. It 
varies still more with variations in its condition of 
moisture. Even in the same individual the re- 
sistance varies materially under apparently 
similar conditions. 

Sleeve, Insulating A tube of treated 

paper or other insulating material, provided 



for covering a splice in an insulated con- 
ductor. 

Sleeve Joint. — (See Joint, Sleeve.) 

Sleeve, Lead A lead tube provided 

for making a joint in a lead-covered cable. 

Sled. — The sliding contacts drawn after a 
moving electric railway car through the slotted 
underground conduit containing the wires or 
conductors from which the driving current is 
taken. 

Slide Bridge.— (See Bridge, Electric, 
Slide Form of.) 

Slide, Resistance A rheostat, in 

which the separate resistances or coils are 
placed in or removed from a circuit by means 
of a sliding contact or key. 

Apparatus employed in telegraphy for 
charging a conductor to a given fraction of 
the maximum potential of the battery so as 
to adjust its charge in order to balance the 
varying charge of a cable. 

The resistance slide consists essentially of a set 
of resistance coils of high insulation and of equal 
resistance. Suppose, for example, ten such equal 
coils to be connected in series, then if connected 
to the charging battery the potential will vary by 
one-tenth at the junction between each pair. A 
condenser, therefore, will be charged to any 
number of tenths of the potential of tha charging 
battery by connecting it at suitable points. 

A second set of coils of equal resistance is ar- 
ranged so as to subdivide any of the lower coils, 
thus permitting an adjustment to within a hun- 
dredth of the potential of the battery. 

Slide Wire.— (See Wire, Slide.) 

Sliding Contact. — (See Contact, Sliding.) 

Slow-Speed Electric Motor. — (See Motor, 
Electric, Slow-Speed?) 

Sluggish Magnet— (See Magnet, Slug- 
gish^ 

Small Calorie. — (See Calorie, Small?) 

Smee Yoltaic Cell. — (See Cell, Voltaic, 
Smee.) 

Smelting, Electro The separation 

or reduction of metallic substances from their 
ores by means of electric currents. 



Sna.] 



479 



[Sol. 



Snap Switch. — (See Switch, Snap.) 
Soaking-In. — A term sometimes employed 
by telegraphers to represent the gradual 
penetration of an electric charge by a neigh- 
boring dielectric. 

An electric displacement occurs in the neigh- 
boring dielectric, and produces thereby what is 
generally called the residual charge. 

Soakiug'-Out. — A term sometimes em- 
ployed by telegraphers to represent a gradual 
discharge which occurs in the case of a 
charged conductor in a neighboring dielec- 
tric. 

When a condenser, or other similar conductor, 
is discharged, the discharge is not instantaneous. 
The charge which soaked in, gradually recovers, 
or soaks- out. 

Socket, Electric Lamp A support 




Fig. jo J. Lanip Socket. 

for the reception of an incandescent electric 
lamp. 

Incandescent lamp sockets are generally made 
so that the mere insertion of the base of the lamp 




Fig. J04. Lamp Socket. 

in the socket completes the connection of the lamp 
terminals with the terminals of the socket. The 



socket terminals are connected with the leads that 
supply current to the lamp; the removal of the 
lamp from the socket automatically breaks its cir- 
cuit. The socket is generally provided with a key 
for turning the lamp on or off without removing 
it from the socket. 

Figs. 503 and 504 show forms of lamp sockets 
for incandescent lamps and the details of the key 
for connecting or disconnecting the lamp with the 
leads. 

Socket, Wall A socket placed in a 

wall and provided with openings for the inser- 
tion of a wall plug with which the ends of a 
flexible twin-lead are connected. 

A wall-socket permits the temporary connec- 
tion of a portable electric lamp, a push button or 
other device with the conductor or lead. 

Soft-Drawn Copper Wire. — (See Wire, 
Copper, Soft-Drawn.) 

Soldering, Electric A process for 

obtaining metallic joints, in which heat gen- 
erated by the electric current is used to melt 
the solder in the place of ordinary heat. 

Solenoid. — A cylindrical coil of wire the 
convolutions of which are circular. 

An electro-magnetic helix. (See Solenoid, 
Electro-Magnetic, or Electro- Magnetic 
Helix) 

A solenoid is termed dextrorsal or sinistrorsal 
according to the direction in which its wire is 
wound. (See Solenoid, Dextrorsal. Solenoid, 
Sinistrorsal.) 

Solenoid Core. — The core, usually of soft 
iron, placed within a solenoid and magnetized 
by the magnetic field of the current passing 
through the solenoid. 

The soft iron core of a solenoid differs from 
that of an electro-magnet in the fact that the core 
of the solenoid is movable, while that of the elec- 
tro-magnet is fixed. (See Magnet, Electro.) 

In order to obtain a nearly uniform pull in its 
various positions in the solenoid, the soft iron cores 
are made of a shape which insures a greater mass 
of metal towards the middle of the core. (See 
Bars, Krizik" 1 s.) 

Solenoid, Dextrorsal A solenoid 

in which the winding is right-handed. (See 
Solenoid, Practical.) 

Solenoid, Electro-Magnetic, or Electro- 
Magnetic Helix The name given to 



Sol.] 



480 



[Sol. 



a cylindrical coil of wire, each of the convo- 
lutions of which is circular. 

A circuit bent in the form of a helix, supported 
at its two extremities, as shown in Fig. 505, and 
traversed by an electric current, will move into 
the magnetic meridian of the place, and, if free to 
move in a vertical plane, will come to rest in the 
line of the magnetic inclination or dip of the place. 

A solenoid traversed by an electric current ac- 
quires thereby all the properties of a magnet, and 
is attracted and repelled by other magnets. Its 
poles are situated at the ends of the cylinder on 
which the solenoid may be supposed to be wound. 

Solenoid, Ideal A solenoid con- 
sisting of a cylinder built up of a number of 
true circular currents, with all faces of like 
polarity turned in the same direction and 
entirely independent of one another. 

The practical solenoid differs from the ideal 
solenoid in that the successive circular circuits or 
currents are all connected with one another in 
series. 

The polarity of a solenoid depends on the direc- 
tion of the current as regards the direction in 
which the solenoid is wound. 

This solenoid is sometimes called an electro- 
magnetic solenoid or helix, in order to distinguish 




Fig, JOS' Practical Solenoid. 

it from a solenoidal magnet. (See Magnet, Sole- 
noidal.) 
A solenoid, if suspended so as to be free to 



move, will come to rest in the plane of the mag- 
netic meridian when traversed by an electric 
current. 

It will also be attracted or repelled by the ap- 
proach of a dissimilar or similar magnet pole 
respectively, as shown in Fig. 505. 

Solenoid, Left-Handed A sinistror- 

sal solenoid or one in which the winding is 
left-handed. (See Solenoid, Practical?) 

Solenoid, Magnetic A spiral coil 

of wire which acts like a magnet when an 
electric current passes through it. 

The magnetic solenoid must be distinguished 
from a solenoidal magnet. (See Magnet, Sole- 
noidal. Solenoid, Electro-Magnetic, or Electro- 
Magnetic Helix.) 

Solenoid, Practical The name ap- 
plied to the ordinary solenoid in order to dis- 
tinguish it from the ideal solenoid. (See 
Solenoid, Ideal) 

A Practical Solenoid consists, as shown in Figs. 




Fig. 506. Practical Solenoid. 
505 and 506, of a spiral coil of wire in which the 
successive circular circuits are connected to one 
another in series. 




Fi g>5o7. Rtght-HandedHeUx, Fig. 508. Left-Handed 
Helix. Fig. fog. Helix, with Consequent Poles. 

The polarity of the solenoid depends on the 
direction of the current, and therefore on the 
direction of winding. In any solenoid, however, 
the polarity may be reversed by reversing the 
direction of the current. (See Magnet, Electro.) 

A Right -Handed, or Dextrorsal Solenoid, is one 
wound in the direction shown in Fig. 507 at I. 



Sol.] 



481 



[Sou. 



A Left -Handed, or Sinistrorsal Solenoid, is one 
wound in the direction shown in Fig. 508 at 2. 

The solenoid shown in Fig. 509 at 3, is wound 
so as to produce consequent poles. (See Poles, 
Consequent. ) 

Solenoid, Eight-Handed A dex- 

trorsal solenoid, the winding in which is right- 
handed. (See Solenoid, Practical?) 

Solenoid, Sinistrorsal A solenoid 

in which the winding is left-handed. (See 
Solenoid, Practical?) 

Solenoidal. — Pertaining to a solenoid. 

Solid Angle. — (See Angle, Solid.) 

Solid Line. — (See Line, Solid.) 

Solution. — A liquid in which another sub- 
stance, generally a solid, is dissolved. 

The liquid may contain either a solid, another 
liquid, or a gas. 

Solution, Bain's Printing- — The 

solution used in Bain's chemical telegraph. 

Bain's solution is made by mixing together one 
part of a saturated solution of potassium ferro- 
cyanide, with two parts of water. 

Solution, Battery The exciting 

liquid for voltaic cells. (See Cell, Voltaic.) 

Solution, Chemical, Bain's A solu- 
tion employed in connection with Bain's re- 
cording telegraph. (See Recorder, Chemical, 
Bain's?) 

Solution, Quicking A solution of 

a salt of mercury, in which objects to be elec- 
tro-plated are dipped after cleansing, just 
before being placed in the plating bath. 

If the articles have been properly cleansed, im- 
mersion in the quicking solution will cover them 
with a uniform, silver-like coating, which will in- 
sure an adherent, uniform coating in the plating 
bath. 

Solution, Saturated A solution in 

which as much of the solid or other substance 
has been dissolved in the liquid as it will take 
at a given temperature. 

Solution, Super-Saturation of 

The condition assumed by a warmed satu- 
rated solution of a salt, when placed in a 
closed vessel out of contact with the air, and 
allowed to cool without being shaken. 

Under the above circumstances the solution 
may be cooled without depositing any crystals. 



Such a solution is said to be super-saturated. It 
will immediately deposit crystals if a crystal of the 
salt dissolved or a crystal of an isomorphous salt 
be dropped in the solution, or often if merely 
shaken. 

It is important in standard voltaic cells in 
which zinc sulphate is used, that the solution be 
saturated but not super- saturated. 



Sonometer, Hughes' 



-An apparatus 



for determining the amount of inductive dis- 
turbance in an induction balance, by compar- 
ing the sounds heard in a telephone, as 
a result of such induction, with the sounds 
heard in the same telephone under circum- 
stances in which the amount of disturbance 
is directly measurable. 

An apparatus devised by Professor Hughes to 
be used in connection with the induction balance, 
in order to measure the amount of disturbance of 
balance produced therein in any particular case, j 

Sonorescence. — A term proposed for the ' 
sounds produced when a piece of vulcanite or 1 
any other solid substance is exposed to a 
rapid succession of flashes of light. (See 
Photophone?) 

Sound. — The sensation produced on the 
brain, through the ear, by the vibrations of a 
sonorous body. 

The sound waves that are capable of pro- 
ducing the sensation of sound on the brain 
through the ear. 

The word sound is therefore used in science in 
two distinct senses, viz.: 

(1.) Subjectively, as the sensation produced by 
the vibrations of a sonorous body. 

(2.) Objectively, as the waves or vibrations that 
are capable of producing the sensation of sound. 

Sound is transmitted from the vibrating body 
to the ear of the hearer by means of alternate to- 
and-fro motions in the air, occurring in every 
direction around the vibrating body and forming 
spherical waves called waves of condensation and 
rarefaction. Unlike light and heat, these waves 
require a tangible medium such as air to trans- 
mit them. 

Sound, therefore, is not propagated in a 
vacuum. The vibrations of sound are longi- 
tudinal, that is, the to-and-fro motions occur in 
the same direction as that in which the sound is 
traveling. The vibrations of light are transverse, 



Sou.] 



482 



[Sou. 



that is, the to-and-fro motions are at right angles 
to the direction in which the light is traveling. 

Sound. — (Objectively.) The waves in the 
air or other medium which produce the sen- 
sation of sound. 

Sound.— (Subjectively.) The effect pro- 
duced on the ear by a vibrating body. 

Sound, Absorption of Acoustic ab- 
sorption. (See Absorption, Acoustic!) 
Sound, Characteristics of The 

peculiarities that enable different musical 
sounds to be distinguished from one another. 

The characteristics of musical sounds are: 

(i.) The Tone or Pitch, according to which a 
sound is either grave or shrill. 

(2.) The Intensity or Loudness, according to 
which a sound is either loud or feeble. 

(3.) The Quality or Ti??ibre, the peculiarity 
which enables us to distinguish between two 
sounds of the same pitch and intensity, but 
sounded on different instruments, as for example, 
on a flute and on a piano. 

Sound, Quality or Timbre of That 

peculiarity of a musical note which enables 
us to distinguish it from another musical note 
of the same tone or pitch, and of the same 
intensity or loudness, but sounded on another 
instrument. 

The middle C, for example, of a pianoforte, is 
readily distinguishable from the same note on a 
flute, or on a violin; that is to say, its quality is 
different. The differences in the quality of musi- 
cal sounds are caused by the admixture of addi- 
tional sounds called overtones which are always 
associated with any musical sound. 

Briefly, nearly all so-called simple musical 
sounds are in reality chords or assemblages of a 
number of different musical sounds. 

In the case of the many different notes that are 
present in an apparently simple note or tone, one 
of the notes is far louder than all the others and is 
called the fundamental tone or note, and is what 
is recognized by the ear as the note proper. The 
others are called the overtones. The overtones 
are too feeble to be heard very distinctly, but 
their presence gives to the fundamental note its 
own peculiar quality. In the case of a note 
sounded on the flute, these overtones are dif- 
ferent either in number or in their relative intensi- 
ties from the same note sounded on another instru- 



ment. Their fundamental tones, however, are 
the same. 

The peculiarities which enable us to distinguish 
the voice of one speaker or singer from another 
are due to the presence of these overtones. The 
overtones must be correctly reproduced by the 
diaphragm of the telephone, or phonograph, 
graphophone, or gramophone, if the articuiate 
speech is to be correctly reproduced witn all its 
characteristic peculiarities. 

Sounder, Morse Telegraphic An 

electro-magnet which produces audible 
sounds by the movements of a lever attached 
to the armature of the magnet. 

The Morse sounder has n w almost entirely 
supplanted the paper recorder or register. On 
short lines it is placed directly in the telegraphic 
circuit. On long lines it is operated by a local 
battery, thrown into or out of the action by the 
relay. (See Relay.) 




F.g j to. Morse Sounder. 

The Morse sounder, shown in Fig. 510, con- 
sists of an upright electro-magnet M, whose soft 
iron armature A, is rigidly attached to the striking 
lever B, working in adjustable screw pivots as 
shown. The free end of the lever is limited in its 
strokes by two set screws N, N. The lower of 
these screws is set so as to limit the approach of 
the armature A, to the poles of the electro-magnet; 
the upper screw is set so as to give the end B, 
sufficient play to produce a loud sound. A re- 
tractile spring, attached to the striking lever near 
its pivoted end, and provided with regulating 
screw S S, pulls the lever back when the current 
ceases to flow through M. 

The dots and dashes of the Morse alphabet are 
reproduced by the sounder, as audible signals, 
that are distinguished by the operator by means 
of the different sounds produced by the up and 
down stroke of the lever as well as by the differ 



Sou.] 



483 



[Sou, 



ence in the intervals of time between the succes- 
sive signals. 

Another form of telegraphic sounder, similar 
in its general construction to that already de- 
scribed, is shown in Fig. 511. 



Sources, Multiple-Arc-Connected 




Fig. 5 XX. Telegraphi 

Sounder, Repeating" 



Sounder. 

— A telegraphic 
sounder which repeats the telegraphic dis- 
patch into another circuit. 

Sounds, Magnetic Faint clicks 

heard on the magnetization of a readily mag- 
netizable substance. 

One of the earlier forms of Reis' telephone, 
operated by means of a rapid succession of these 
faint magnetic sounds. 

Source, Electric Any arrangement 

capable of maintaining a difference of poten- 
tial or an electromotive force. 

The following are the more important electric 
sources, arranged according to the character of 
the energy which is converted into electric 
energy. 

Electric Sources. 

1. Voltaic Cell or Primary "| 

Battery. 

2. Charged Storage Cell or 

Secondary Battery. 
-x. Thermo Cell or Thermo 



Battery. 
Selenium Cell 



Chemical Poten- 
tial Energy. 



Radiant Energy. 



Ma- ~\ 



or Sele- 
nium Battery. 

5. Magneto - Electric 

chine. 

6. Dynamo-Electric Ma- 

chine. 

7. Frictional Electric Ma- 

chine. 

8. Electrostatic Induction 

Machine. 

9. Magneto-Electric Tele- 

phone Transmitter. 

Heat and Mechan- 
ical Energy. 

31. Animal or Plant Vital Energy. 



Mechanical 
Energy. 



10. Pyromagnetic Generator. 



A term sometimes applied to sources connect- 
ed in multiple. (See Sources, Multiple-Co?i- 
nected.) 
Sources, Multiple-Connected The 

connection of a number of separate sources 
so as to form a single source by joining the 
positive poles of all the separate sources to a 
single positive lead or conductor, and all the 
negative poles to a single negative lead or 
conductor. 

The multiple connection of sources results in 
each of the sources discharging its current into 
the main conductor in a direction parallel to 
that of the other sources. 

The electromotive force in the same is that of 
any single source, but the resistance of the com- 
bined source decreases with each source added. 
Supposing the resistance of each source be the 
same, then if ten such sources are connected in 
multiple -arc, the resistance of the combined source 
is but one-tenth the resistance of a single source. 
(Sc-e Circuit, Multiple.) 

Sources are combined in multiple-arc whenever 
the current furnished by the separate sources is 
insufficient to properly operate the electro-recep- 
tive or translating device with which it is con- 
nected. 

Sources, Multiple-Series-Connected 

— The conection of a number of separate 
sources so as to form a single source by con- 
necting a number of the sources in groups 
in series, and joining these groups together 
in multiple-arc. 

The battery of sources obtained by connecting 
a number of separate sources in multiple-series 
will have an electromotive force equal to the 
sum of the separate electromotive forces of the 
sources connected in any of the separate series- 
connected groups. 

The current produced will be greater in propor- 
tion to the number of separate groups in parallel. 
The internal resistance will be increased in pro- 
portion to the number of coils in series, and de- 
creased in proportion to the number of groups in 
multiple-arc or parallel. 

Sources are connected in multiple-series when 
both the electromotive force and the current of 
any single source are insufficient to operate the 
electro-receptive or translating device. (See 
Circuit, Multiple- Series . ) 



Sou.] 



484 



[Spa, 



Sources, Parallel ■ Connected A 

term sometimes applied to multiple-connected 

sources. (See Sources, Multiple-Connected) 

Sources, Series-Connected The 

connection of a number of separate electric 
sources so as to form a single source, in 
which the separate sources are placed in a 
single line or circuit by so connecting their op- 
posite poles that the current produced in each 
passes successively through each of the 
sources. 

The series-connection of sources results in an 
electromotive force equal to the sum of the sepa- 
rate electromotive forces produced by each 
source — that is, a rise of potential occurs with each 
source added. This connection increases the re- 
sistance of the circuit by the amount of the resist- 
ance of each source introduced into the circuit. 
The value of the resulting current depends on the 
total electromotive force and resistance of the 
series- connected sources. 

Sources are connected in series when the 
electromotive force furnished by a single source 
is insufficient for the character of work required 
to be done. (See Circuit, Series.) 

Sources, Series-Multiple-Connected 

— The connection of a number of separate 
electric sources, so as to form a single source, 
in which the separate sources are connected 
in a number of separate multiple groups or 
circuits, and these groups or circuits separ- 
ately connected together in series. (See Cir- 
cuit, Series-Multiple) 

Southern Light. — A name sometimes given 
to the Aurora Australis. (See Aurora Aus- 
tralis.) 

Space, Clearance The space be- 
tween the revolving armature of a dynamo- 
electric machine, or electric motor, and the 
polar faces of the pole pieces. 

Space, Dark, Crookes' A dark 

space surrounding the negative electrode in a 
rarefied space through which electric dis- 
charges are passing. 

Crookes' dark space lies immediately between 
the negative electrode and its glow or luminous 
discharge. It differs, therefore, from Faraday's 
dark space, which lies between the luminous dis- 
charges of the negative and positive electrodes. 



The radius of Crookes' dark space increases 
with the degree of exhaustion. It varies also 
with the character of the residual gas, with the 
temperature of the negative electrode, and some- 
what with the intensity of the spark. When the 
vacuum becomes sufficiently high, the dark space 
fills the entire tube through which the discharges 
are passing. 

Crookes has found that in the case of substances 
that become phosphorescent under the electric 
discharge, phosphorescence best takes place when 
the body is placed on the boundary of the dark 
space. 

Space, Dark, Faraday's The gap 

in the continuity of the luminous discharges 
that occurs between the glow of the positive 
and negative electrodes. 

Faraday's dark space is seen in a partially ex- 
hausted tube through which the discharges of 
an induction coil are passing. It occurs in as 
low a vacuum as 6 millimetres of mercury. 
As the vacuum becomes higher, the length of the 
dark space increases. 

Space, Inter-Air A term some- 
times employed for the air space between the 
outer surface of the revolving armature of a 
dynamo-electric machine and the adjacent 
faces of the pole pieces. (See Space, Clear- 
ance.) 

Space, Interferric A term some- 
times used for air gap. (See Gap, Air.) 

Span Wire. — (See Wire. Span) 

Spark Coil. — (See Coil, Spark) 

Spark Gap. — (See Gap, Spark.) 

Spark, Length of The length of 

spark that passes between two charged con- 
ductors depends : 

(i.) On the difference of potential between 
them. 

(2.) On the character of the gaseous medium 
that separates the two conductors. 

(3.) On the density or pressure of the gaseous 
medium between the conductors. 

Up to a certain pressure, a decrease in the 
density causes an increase in the length of the 
distance the spark will pass- When this limit is 
reached, a further decrease of density decreases 
the length of spark. A high vacuum prevents 
the passage of a spark even under great differ- 
ences of potential. 



Spa.] 



485 



[Spa. 



(4.) On the kind of material that forms the 
electrodes between which the charges pass. 

(5.) On the shape of the charged conductor. 

(6. ) On the direction of the current. 

Sparks from the prime conductor are denser 
and more powerful than those from the negative 
conductor. 

It will be observed that the length of the spark 
practically depends mainly on two circumstances, 
viz., on the differences of potential of the oppo- 
site charges, and the conducting power of the 
medium that separates the two bodies. 

Spark, "["-Shaped - — - — A variety of 
three-branched spark obtained by the dis- 
charge of a Leyden jar through a peculiar 
form of induction coil. (See Spark, Three- 
Branched^) 

Spark, Three-Branched — A pecu- 
liar form of branched spark obtained by the 
discharge of a Leyden jar through a peculiar 
form of induction coil. 

The three-branched spark was obtained by 
Elihu Thomson by the use of the following appa- 
ratus: The discharges of a Leyden jar, charged by 
a T5pler-Holtz machine, were sent through an in- 
duction coil, the primaVy and secondary of which 



/ 


— ) 


( 


-~ 




I 


_---' 


> 


I ----- 




> 


t 




) 


1 ----- 




r^r 




Fig. J 1 2. Apparatus for Three-Branched Sparks. 
were of few turns. The circuit connections were 
as shown in Figs. 512 and 513, and the apparatus 
is described by Thomson as follows: 

"A double coil was made, Fig. 512, in which 
the inner turns were about twelve and the outer 
turns twenty. These were kept separate from each 
other and a branch wire taken from the line and 
slid from point to point on the outer wire enabled 
the effective length of the same to be adjusted. 
The inner coil was connected through a small 
spark gap, as at A, to the outer coating of a Ley- 
den jar, while the wire L, was brought near the 
pole of the jar, which was continually being 



charged from a Topler-Holtz machine. The 
discharge, in passing from the knob of the jar to 
the wire L, representing the line, passed by the 



Oi*Q 




J 13. Apparatus/or T and Y Shaped Sparks. 

inner coil. When a certain length of the outer 
coil was employed, only a very short, almost im- 
perceptible spark was obtainable at a. If the 
balance of the turns were disturbed by including 
more or less than the proper number of the outer 
turns, not only did a vigorous spark occur, but 
the gap at a, could be quite considerably extended, 
in accordance with the amount of departure taken 
from the proper number of turns required to pro- 
duce the balance. This ex- 
periment indicates that it is 
possible to make a selective 
path for the Leyden jar dis- 
charge, and to have a struc- 
ture so proportioned that 
the discharges reaching line 
will pass to earth without -^in- 
tending to go through the cir- 
cuit of the dynamo. The action is apparently 
due to a balance of electromotive forces such 
that the discharge which tends to pass from the 
line in going to earth induces in the coil con- 
nected to the dynamo a counter electromotive 
force which nearly wipes out the potential of the 
discharge before it reaches the dynamo. This 
balance of inductive effects is certainly very strik- 
ing, and once obtained, it is disturbed, as, in the 
experiments, by changing the relative lengths of 
the coils in inductive relation through so small 
an amount as an inch or two. 

" It may be mentioned here that some curious 




Si 4. Three- 
Branched Sparks. 



Spa.] 



486 



[Spe. 



effects of spark were obtained in these experi- 
ments. When a disturbance of the balance ex- 
ists and a spark is obtained at a, the character of 
the spark is different from that of the Ley den jar 
discharge. It appears to be less luminous, the 
noise less sharp, and its color would indicate a 
greater power of volatilizing metal and perhaps a 
greater duration. It is in part," no doubt, due to 
a current local to the coils in series with one an- 
other. 

"Another curious effect was the production of 
T-shaped and Y" sna P e( i sparks, or three- 
branched sparks (such as are shown in Figs. 513 
and 514.)" 

" These were obtained by separating the elec- 
trodes at A, an inch and a half or thereabouts, 
and bringing the third electrode from the outer 
coil to the position shown in Fig. 513. The dis- 
charges were now obtained as before from the 
charged jar. In this case the discharge appears 
to split and unite in air, producing the curious 
shaped sparks shown. It would seem that to ob- 
tain these effects — particularly the sparks which 
were three-branched from a common point in the 
centre between the discharge electrodes —the 
dielectric air must break down simultaneously be- 
tween the three electrodes. It would easily ex- 
plain the X- sna P es to assume the straight part 
above to form first, and the cross or transverse 
spark to strike from the side of this spark to the 
third electrode." 

Spark Tube.— (See Tube, Spark,) 

Spark, Wipe In an electric gas- 
lighting pendant burner, a spark obtained 
from a spark coil by the wiping contact of a 
spring, moved by the pulling of the pendant. 
(See Burner, Ratchet-Pendant, Electric?) 

Spark, Y-Shaped A variety of three- 
branched spark obtained by the discharge of 
a Leyden jar through a peculiar form of induc- 
tion coil. (See Spark, Three-Branched) 

Sparking" Discharge.— (See Discharge, 
Disrtiptive) 

Sparking Distance.— (See Distance, 
Sparking.) 

Sparking-, Line of Least The line 

on a commutator cylinder of a dynamo con- 
necting the points of contact of the collecting 
brushes where the sparking is a minimum. 

In some forms of dynamos the line of least 



sparking lies parallel to the lines of magnetic 
force of the field. 

In most forms, however, it is at right angles to 
such lines. The exact position of all these lines 
is changed by the angular lead of the brushes. 
(See Lead, Angle of.) 

Sparking of Dynamo-Electric Machine.— 

(See Machine, Dynamo-Electric, Sparking 
of) 

Spar Torpedo.— (See Torpedo, Spar.) 

Spasmodic Governor.— (See Governor, 
Spasmodic.) 

Speaking-Tube Annunciator.— (See An- 
nunciator, Oral or Speaking- Tube) 

Speaking-Tube Mouth Piece, Electric 

Alarm A mouth piece for a speaking 

tube, so arranged, that the movement of a 
pivoted plate covering the mouth piece au- 
tomatically rings a bell at the other end of 
the tube. 

Specific Conduction Resistance.— (See 
Resistance, Specific Conduction) 

Specific Conductivity. (See Conduc- 
tivity, Specific) m 

Specific Heat— (See Heat, Specific) 

Specific Heat of Electricity.— (See Elec- 
tricity, Specific Heat of) 

Specific Hysteresial Dissipation. — (See 
Dissipation, Specific Hysteresial) 

Specific Inductive Capacity. — (See Ca- 
pacity, Specific Inductive) 

Specific Magnetic Capacity. — (See Ca- 
pacity, Specific Magnetic) 

Specific Magnetic Conductivity. — (See 
Conductivity, Specific Magnetic) 

Specific Magnetic Inductivity. — (See In- 
ductivity, Specific Magnetic) 

Specific Resistance. — (See Resistance, 
Specific) 
Specific Resistance of Liquids.— (See 

Resistance, Specific, of Liquids) 

Speech, Articulate The successive 

tones of the human voice that are necessary 
to produce intelligible words. 

The phrase articulate speech refers to the join- 
ing or articulation of the successive sounds in- 
volved in speech. The receiving diaphragm of a 



Spe. 



487 



LSpo. 



telephone is caused to reproduce the articulate 

speech uttered near the transmitting diaphragm. 

■ 
Speed, Critical, of Compound-Wound 

Dynamo The speed at which both the 

series and shunt coils of the machine give the 

same difference of potential when the full load 

is on the machine, as the shunt coil would if 

used alone on open-circuit. 

Speed Indicator. — (See Indicator, Speedy 

Speeding. — Varying the number of revolu- 
tions per minute. 

The speeding of a dynamo is for the purpose 
of obtaining the current requisite to properly 
operate the electro -receptive device placed in its 
circuit. 

Spent Acid. — (See Acid, Spent?) 

Spent Liquor. — (See Liquor, Spent.) 

Spherical Armature. — (See Armature, 
Spherical) 

Sphygniograni. — A record made by a 
sphygmograph. (See Sphygmograph) 

Sphygmograph. — An instrument for re- 
cording the peculiarities of the normal or 
abnormal pulse. 

Sphygmograph, Electrical An in- 
strument for electrically recording the peculi- 
arities of the pulse. 

Sphyginophone. — An apparatus in which 
a microphone is employed for the medical 
examination of the pulse. (See Microphone) 

Spider, Armature A light frame- 
work or skeleton consisting of a central sleeve 
or hub keyed to the armature shaft, and pro- 
vided with a number of radial spokes or arms 
for fixing or holding the armature core to 
the dynamo-electric machine. 

Spider, Driving Radial arms or 

spokes connected to the armature of a dynamo- 
electric machine and keyed to the shaft so as 
to act as a driving wheel for the armature. 

Spin, Magnetic A term sometimes 

employed instead of magnetic field. 

The term magnetic spin is sometimes used in- 
stead of magnetic field because the magnetism is 
now generally believed to be due to the effects of 
a rotary motion or spin in the surrounding uni- 
versal ether. 



Spiral, Primary 



-The primary of an 



induction coil or transformer. (See Trans- 
former. Coil, Induction) 

Spiral, Roget's A suspended wire 

spiral conveying a strong electric current and 
devised to show the attractions produced by 
parallel currents flowing in the same direc- 
tion. 

The lower end of the wire spiral dips into a 
mercury cup. On the passage of the current, the 
attraction of the neighboring turns of the spiral 
for each other shortens the length of the spiral 
sufficiently to draw it out of the mercury and thus 
break the circuit. When this occurs the weight 
of the spiral causes it to fall and again re-estab- 
lish the circuit. A rapid automatic-make-and- 
break is thus established, accompanied by a brill- 
iant spark at the mercury surface due to the ex- 
tra spark on breaking*. 

Spiral, Secondary The secondary 

coil of an induction coil or transformer. (See 
Transformer. Coil, Induction) 

Splice Box.— (See Box, Splice) 
Split Battery.— (See Battery, Split) 
Split Lead Tee.— (See Tee, Split Lead.) 
Spluttering of Arc. — (See Arc, Splutter- 
ing of) 

Spots, Sun Dark spots, varying in 

number and position, which appear on the 
face of the sun and are believed by some to be 
caused by huge vortex motions in the masses 
of glowing gas that surround the sun's body. 
Sun spots occur in greater number at intervals 
of about every eleven years. 

Their occurrence is generally attended with 
unusual terrestrial magnetic variations. (See 
Storm, Magnetic) 

In the opinion of most astronomers the sun 
spots mark depressions in the atmosphere of the 
sun. Their exact causes are unknown, though 
they appear to be dependent on a local cooling 
or condensation of the sun's atmosphere. 

When observed through a telescope the sun 
spot appears as a dark region surrounded by a 
less dark region. Though darker by contrast 
with tht. rest of the sun's face, yet such spots are 
in reality much brighter than the most brilliant 
arc light. The outline of the sun spot is quite 
irregular. 



Spr.] 



488 



[Sta. 



Spreading-Out Magnetic Field.— (See 
Field, Magnetic, Spreading-Out ) 

Sprengel Mercury Pump. — (See Pump, 
Air, Spr eng el's Mercurial) 

Spring Ammeter. — (See Ammeter, 
Spring?) 

Spring Contact. — (See Contact, Spring) 

Spring, Hold-Off A spring which 

acts to keep one thing away from another in 
opposition to some force tending to keep it in 
contact with such a thing. 

Spring, Hold-On A spring which 

acts to keep one thing against another in op- 
position to some force tending to pull it 
away. 

A hold- on spring is sometimes employed in a 
dynamo -electric machine for the purpose of keep- 
ing the collecting brushes in proper pressure 
against the segments of the commutator. 

Spring-Jack. — A device for readily insert- 
ing a loop in a main electric circuit. The 
spring-jack is generally used in connection 
with a multiple switch board. (See Board, 
Multiple Switch) 

Spring-Jack Cut-Out. — (See Cut-Out, 
Spring-Jack) 

Spurious Hall Effect.— (See Effect, Hall, 
Spurious) 

Spurious Eesistance. — (See Resistance, 
Spurious) 

Stabile Galvanization. — (See Galvaniza- 
tion, Stabile) 

Staggering. — A term sometimes applied to 
the position of the brushes on a commutator 
cylinder, in which one brush is placed slightly 
in advance of the other brush so as to bridge 
over a break. 

When a break occurs in the circuit ot the arma- 
ture wires, the device of staggering the brushes is 
adopted for temporarily bridging over the break. 
When a break occurs, the rewinding of the arma- 
ture is the only radical cure. 

Standard Candle. — (See Candle, Stand- 
ard) 



Standard Carcel Gas Jet.— (See Jet, Gas r 
Carcel Standard) 

Standard, Dynamo The supports 

for the bearings of a dynamo-electric ma- 
chine. 

Standard Earth Quadrant— (See Quad- 
rant, Standard) 

Standard of Self-induction, Ayrton & 

Perry's (See Induction, Self, Ayrton 

&° Perry's Standard of) 

Standard Ohm. — (See Ohm, Standard) 

Standard, Pentane A standard 

source of light used in photometric measure- 
ments, in place of a Methven screen. 

The pentane standard is constructed in general 
in the same manner as the Methven standard. 
In place, however, of ordinary coal gas, a mixture 
of pentane and air is used. Pentane is a variety 
of coal oil left after several distillations of ordinary 
crude oil. It distills at a temperature not greater 
than 50 degrees centigrade. 

The mixture for burning consists of about 
twenty volumes of air to seven volumes of pen- 
tane. A burner of the pentane standard is some- 
what similar to the Methven standard, but differs 
in a number of minor details. 

Standard Resistance Coil. — (See Coil, 
Resistance, Standard) 

Standard Size of Electrodes, Erb's 

— (See Electrodes, Erb's Standard Size of) 

Standard Yoltaic Cell.— (See Cell, Voltaic, 
Standard) 
Standard Voltaic Cell, Clark's 

(See Cell, Voltaic, Standard, Clark's) 

Standard Yoltaic Cell, Clark's, Rayleigh's 
Form of (See Cell, Voltaic. Stand- 
ard, Rayleigh's Form of Clark's) 

Standard Yoltaic Cell, Fleming's 

(See Cell, Voltaic, Standard,' Fleming's) 

Standard Yoltaic Cell, Lodge's 

(See Cell, Voltaic, Standard, Lodge's) 

Standard Yoltaic Cell, Sir William 
Thomson's (See Cell, Voltaic, Stand- 
ard, Sir William Thomson's) 

Standard Wire Gauge. — (See Gauge, 
Wire, Standard) 



Sta.] 



489 



[Sta. 



Standardizing a Voltaic Cell. — (See Cell, 
Voltaic, Standardizing a) 

Standards, Motor A name applied 

to the supports for the bearings of an electric 
motor. 

State, Allotropic A modification 

of a substance, in which, without changing 
its chemical composition, it assumes a condi- 
tion in which many of its physical and chem- 
ical properties are different from those it or- 
dinarily possesses. 

Thus the element carbon occurs in three widely 
different allotropic states, viz.: 

(i.) As charcoal, or ordinary carbon; 

(2.) As graphite, or plumbago; and 

(3.) As the diamond. 

State, Anelectrotonic The condi- 
tion of decreased functional activity which 
occurs in a nerve in the neighborhood of the 
anode or positive terminal of a source to 
whose influence it is subjected. (See Anelec- 
trotonus.) 

State, Electrotonic — A peculiar 

state supposed by Faraday to exist in a wire or 
other conductor, whereby differences of po- 
tential are produced by means of its move- 
ment through a magnetic field. 

In his early researches Faraday regarded this 
state as a necessary condition in which a wire or 
conductor must exist, prior to its movement 
through a magnetic field, in order to have a dif- 
ference of potential produced; but at a later day 
he abandoned this idea, and explained the true 
causes of electrodynamic induction. (See In- 
duction, Electro-Dynamic. ) 

The term electrotonic state is to be carefully dis- 
tinguished from electrotonus, or the change pro- 
duced in the functional activity of a nerve by an 
electric current. (See Electrotonus.) 

State, Kathelectrotonic The con- 
dition of increased functional activity of a 
nerve in the neighborhood of the kathode or 
negative terminal of a source to whose in- 
fluence it is subjected. (See Kathelectro- 
tonus.) 

The kathelectrotonic state is one of the states 
or conditions of electrotonus or altered functional 
activity produced in a nerve by an electric cur- 
rent. (See Electrotonus.) 



State, Nascent —A term used in 

chemistry to express the state or condition of 
an elementary atom or radical just liberated 
from chemical combination, when it possesses 
chemical affinities or attractions more ener- 
getic than afterwards. 

According to Grothuss' hypothesis, during the 
decomposition of a chain of polarized molecules, 
such for example as in the case of hydrogen sul- 
phate, H 2 S0 4 , in a zinc-copper voltaic cell, the 
two atoms of hydrogen H & , liberated by the com- 
bination of the S0 4 , with an atom of zinc, Zn, pos- 
sess a stronger affinity for the S0 4 of the molecule 
next to it, than does its own H 2 , and thus liber- 
ates its two atoms of hydrogen, which in turn 
unite with the S0 4 , of the next molecule in the 
polarized chain, and this continues until the two 
atoms of hydrogen liberated from the last mole- 
cule in the chain are given off at the copper plate. 
(See Hypothesis, Grothuss* .) 

The peculiar properties characteristic of the 
nascent state of elements is doubtless due to 
the fact that the elements are then in a, free 
state, with their bonds open or tinsatisjied, and 
therefore possess greater affinities than when they 
are united in molecules. Thus H — , H— , or 
atomic hydrogen, should possess different affinities 
than H— H, or molecular hydrogen. 

State, Passive The condition of a 

metallic substance in which it may be placed 
in liquids that would ordinarily chemically 
combine with it, without being attacked or 
corroded. 

It is very doubtful whether metallic bodies can 
be properly regarded as possessing an actual 
passive state. Iron, for example, which is one of 
the metals that is said to be capable of assuming 
this so-called passive state, can be placed in this 
condition by immersing it for a few moments in 
concentrated nitric acid, and subsequently wash- 
ing it. It will then, unlike ordinary iron, neither 
be attacked by concentrated nitric acid, nor will 
it precipitate copper from its solutions. This 
condition is now generally believed to be due to 
the formation of a thin coating of magnetic oxide 
on its surface. 

Many of the instances of the so-called passive 
state are simply cases of the well known electrical 
preservation of metals that form the negative 
element of a voltaic combination, under which 
circumstances the positive element only of the 



Sta.J 



490 



[Ste 



voltaic couple is chemically attacked by the elec- 
trolyte. (See Cell, Voltaic. Metals, Electrical 
Protection of. ) 

State, Permanent, of Charge on Tele- 
graph Line The condition of the 

charge on a telegraph wire when the current 
reaching the distant end has the same 
strength as at the sending end. 

State, "Variable, of Charge of Telegraph 

Line — The condition of the charge on 

a telegraph wire while the strength of the 
current is increasing up to the full strength 
in all parts. 

The duration of the variable state is directly as 
the length of the line, the electrostatic capacity 
and the total resistance. It is increased by leak- 
age, by static capacity and by the effects of the 
extra current. (See Currents, Extra.) 

Static Breeze. — (See Breeze, Static?) 

Static Electricity. — (See Electricity, 
Static?) 

Static Energy. — (See Energy, Static?) 

Static Hysteresis. — (See Hysteresis, 
Static?) 

Static Insulation. — (See Insulation, 
Static?) 

Static Magnetic Induction.— (See Induc- 
tion, Magnetic, Static?) 

Static Shock. — (See Shock, Static?) 

Statics. — The science which treats of the 
relations that must exist between the points 
of application of forces and their direction 
and intensity, in order that equilibrium may 
result. 

Statics, Electro That branch of 

electric science which treats of the phenome- 
na and measurement of electric charges. 

Some of the more important principles of elec- 
trostatics are embraced in the following laws: 

(I.) Charges of like name, i. e., either positive 
or negative, repel each other. Charges of unlike 
name attract each other. 

(2.) The forces of attraction or repulsion be- 
tween two charged bodies are directly propor 
tionai to the product of the quantities of electricity 
possessed by the bodies and inversely proportional 
to the square of the distance between them. 



These laws can be demonstrated by the use of 
Coulomb's torsion balance. (See Balance, Cou- 
lomb' l s Torsion?) 

Statics, Magneto That branch of 

magnetism which treats of magnetic attrac- 
tions and repulsions, the distribution of lines 
of magnetic force and other facts regarding 
fixed magnets. 



Station, Central 



-A station, cen- 



trally located, from which electricity for light 
or power is distributed by a series of con- 
ductors radiating therefrom. 

Station, Distant A term applied by 

an operator to the distant end of the line in 
order to distinguish it from his own end. 

Station, Distributing A station 

from which electricity is distributed. 
A central station. 



■A term applied by 



Station, Home — 

an operator to his end of the line, in order to 
distinguish it from the other or distant sta- 
tion. 

Station, Transforming In a system 

of distribution by transformers or converters 
a station where a number of transformers are 
placed, in order to supply a group of houses 
in the neighborhood. (See Transformer. 
Electricity, Distribution of, by Alternating 
Currents?) 

Stationary Floor Key. — (See Key, Sta- 
tionary Floor?) 

Stationary Torpedo. — (See Torpedo, Sta- 
tionary.) 

Stay Rods, Telegraphic Metal rods 

attached to a telegraph pole, and securely 
fastened in the ground in order to counteract 
the effects of a pull or tension on the poles. 
(See Pole, Telegraphic.) 

Stay rods should be used in all exposed situa- 
tions, or where the poles are exposed to severe 
strains. 

Steady Current.— (See Current. Steady?) 

Stearns' Relay Shunt.— (See Shunt, Re- 
lay, Stearns .) 

Steel, Qualities of, Requisite for Mag- 
netization Qualities which must be 



SteJ 



491 



[Sto- 



possessed by steel in order to permit it to per- 
manently retain a considerable magnetization. 

For the purposes of permanent magnetization 
steel should possess the following qualities: 

It should be hard and fine grained. Hard cast 
steel answers the purpose very well. Scoresby 
showed that an intimate relation exists between 
the quality of the iron from which the steel is 
made, and the ability of the steel to take and re- 
tain considerable magnetism. 

The steel should be hardened as high as possi- 
ble and the temper afterwards drawn by heat to 
a violet-straw color. Practice is not uniform in 
this respect, the exact color varying with the 
quality of the steel. 

An admixture with the steel of about y^ of one 
per cent, of tungsten is said to increase its mag- 
netic powers. 

Cast steel is not generally employed for mag- 
nets, wrought steel being generally preferred. 

Step-by-Step, or Dial Telegraphy.— (See 

Telegraphy, Step-by-Step.) 

Step-Down Transformer. — (See Trans- 
former, Step-Down.) 

Step-Up Transformer. — (See Transform- 
er, Step- Up) 

Sterilization, Electric Sterilizing 

a solution by depriving it of whatever germs 
it may contain by means of electrical cur- 
rents. 

The following experiments were recently made 
on sterilization by means of electric currents: 
The fluid, with the culture, was placed in a glass 
test tube, wound about with a wire coil connected 
either with a dynamo or accumulator or other 
electric source. Some increase in temperature 
was made, but never over 98 Fahr. When a 
current 1. 25 volts, 2.5 amperes passed, a com- 
plete sterilization of Micrococus Prodigiosus oc- 
curred at the end of twenty-four hours. 

Blood and water containing pathogenic germs 
was sterilized in five to thirty minutes. The 
above described effects would appear to be mag- 
netic rather than electric. 

Sticking. — A word applied by telegraphers 
to the failure of the positive pole relay arma- 
ture to leave the magnet pole on the cessation 
of the current. 

In telegraphy, when from any cause a circuit 
is imperfectly broken by an operator's key, or at 



the points of contact of a relay or other instru- 
ment, such failure is called sticking. When an arc 
is formed at the points of a relay where the local 
circuit is made and broken, the relay " sticks. " 
The arc is caused by burning of the platinum, 
points. Sticking may be a result of a too weak 
retractile spring. 

Stone, Hercules A name given by 

the ancients to the lodestone. (See Lode- 
stone) 

Stool, Insulating A stool provided 

with insulating supports of vulcanite or other 
insulator, employed to afford a ready insulat- 
ing stand or support. 

Stop, Limiting' A stop set so as to 

limit the motion of an electrically vibrating or 
oscillating bar to any predetermined extent. 

Such limiting stops are common on telegraphic 
and various other electrical apparatus. 

Stopping-Off. — A process employed in 
electro-plating, in which a metallic article, al- 
ready electro-plated over its entire surface, is 
electro-plated with another metal over certain 
parts only. 

The process of stopping-off consists of covering 
the parts which are to receive the metallic coat- 
ing, with various stopping-off varnishes. By this 
means articles can be electro-plated on parts of 
their surfaces with gold and on the remainder 
with silver. The whole surface is first silvered, 
and the portions intended to be afterwards gilded 
are then stopped off and the object placed in the 
gilding bath. 

Stopping-Off Tarnish. — (See Varnish, 
Stopping-Off.) 
Storage Battery. — (See Battery, Storage) 
Storage Capacity of Secondary Cell. — 

(See Cell, Secondary or Storage, Capacity 
of) 

Storage Cell. — (See Cell, Storage) 

Storage of Electricity. — (See Electricity, 
Storage of) 

Storm, Auroral A term sometimes 

employed to express an unusual prevalence 
of auroras. 

Storm, Electric An unusual con- 
dition of the atmosphere as regards the quan- 
tity of its free electricity. 



Sto.J 



492 



[Str. 



A thunder storm is a variety of electric storm. 
(See Storm, Thunder.) 

Storm, Magnetic Irregularities oc- 
curring in the distribution of the earth's 
magnetism, affecting the magnetic declina- 
tion, dip, and intensity. 

Magnetic storms have been observed to accom- 
pany auroral displays, and to be coincident with 
the occurrence of sun spots, or unusual outbursts 
of solar activity. 

The coincidence of magnetic storms and out- 
bursts of solar activity is unquestioned. Wolf, 
of Zurich, has shown by a comparison of nu- 
merous observations of sun spots, the unques- 
tioned correspondence, in the times of their 
greatest activity, which occur every 1 1 . 1 years, 
with the time of occurrence of an unusual number 
of sun spots. He has placed these results in the 
form of curves. Those shown in Fig. 515 are 
taken from observations at Paris and Prague. 
The full lines represent the periods of sun spots. 
The dotted lines the periods of magnetic storms. 




Fig. 515. Wolfs Sun Spot Numbers. 



Storm, Thunder 



-A storm during 



which electrical discharges accompanied by 
thunder take place between two clouds or be- 
tween a cloud and the earth. (See Elec- 
tricity, Atmospheric. Storms, Thunder, 
Geographical Distribution of) 

Storms, Thunder, Geographical Dis- 
tribution of The following general 

facts as to the geographical distribution of 
thunder storms, show the intimate relation 
between the frequency of thunder storms and 
the time and place of the condensation of 
vapor. 

( 1 . ) Thunder storms seldom, if ever, occur in 
the polar regions. 

This is probably because the rainfall in the 



polar regions results from the condensation of the 
vapor that was formed in the equatorial or tem- 
perate regions, so that a considerable time 
elapses between the evaporation and condensa- 
tion. 

(2.) Thunder storms seldom, if ever, occur in 
rainless districts, owing probably to the absence 
of the condensation of vapor. 

(3.) Thunder storms are most frequent and 
violent in the equatorial regions, where the rain- 
fall results from the condensation of the vapor by 
the action of ascending currents, conveying the 
vapor almost immediately after its formation into 
the upper and colder regions of the atmosphere. 

(4.) Thunder storms occur in regions beyond 
the tropics, at those seasons of the year when the 
rainfall results from the condensation of the vapor 
shortly after the time of its formation, viz., in the 
temperate zones in the hotter parts of the year. 

Straight-Line Trolley Hanger. — (See 
Ha?iger, Straight-Line Trolley) 

Straightaway Bundled Cable. — (See 
Cable, Bunched, Straightaway) 

Strain, Dielectric The strained 

condition in which the glass, or other dielec- 
tric of a condenser, is placed by the charging 
of the condenser. 

The deformation of a body under the in- 
fluence of a stress. (See Stress.) 

The stress in this case, i. e., the force produc- 
ing the deformation or strain, is the attraction of 
the opposite charges. This stress, in the case of 
a Leyden jar, is often sufficiently great to cause 
a rupture of the glass. 

Strain, Electro-Magnetic The de- 
formation produced by an electro-magnetic 
stress. (See Stress, Electro-Magnetic) 

Strain, Electrostatic, Optical A 

strain or deformation produced in a plate of 
glass, or other transparent solid, by subject- 
ing it to the stress of an electrostatic field. 
(See Stress, Electrostatic) 

To obtain the electrostatic stress, holes are 
drilled in the plate of glass, and wires from a 
Holtz machine or induction coil placed therein, 
the wires being separated by a thin layer of glass. 

The glass, on being traversed by a beam of 
plane polarized light, rotates the plane of polar- 
ization of the light in the same direction as the 
glass would if subjected to a strain in the direc- 



Str.] 



493 



[Str. 



Hon of the lines of electric force. (See Rotation, 
Magneto- Optic. ) 

Strain, Magnetic The deformation 

produced in the air-gap between two dissimi- 
lar magnetic poles, or in any substance placed 
therein, by the stress of the lines of magnetic 
force bridging such gap. 

Strain, Optical A deformation or 

alteration of volume produced in a plate of 
glass, or other transparent medium, by the 
action of any stress. (See Strain, Electro- 
Magnetic. Strain, Electrostatic, Optical) 

Strain, Optical Electro-Magnetic 

A strain produced in a plate of glass or other 
transparent medium by placing it in a mag- 
netic field. (See Stress, Electro-Magnetic . 
Rotation, Magneto-Optic) 

Optical strain, whether electrostatic or mag- 
netic, or even mechanical, often causes a medium 
to acquire the power of double refraction or ro- 
tary polarization. (See Refraction, Double, 
Electric. Rotation, Magneto-Optic.) 

Stranded Core of Cable. — (See Core, 

Stranded, of Cable) 
Stranded Line. — (See Line, Stranded.) 
Strap Copper.— (See Copper, Strap.) 
Straps and Climbers. — Devices employed 

by linemen for climbing wooden telegraph 

poles. 
Stratham's Electric Fuse. — (See Fuse, 

Electric, Stratham's) 

Stratification Tube. — (See Tube, Stratifi- 
cation) 

Stratified Discharge. — (See Discharge, 
Stratified) 

Stray Field. — (See Field, Magnetic, 
Stray) 

Stray Power. — (See Power, Stray) 

Stream-Lines of an Escaping Fluid. — 
Lines which show the actual path of the 
particles of an escaping fluid. 

When the escape has reached a steady condi- 
tion, the stream-lines correspond to the flow lines. 

Streamers.— Pillars or parallel flashing 
columns of light frequently seen during the 
prevalence of an aurora. (See Aurora Bo- 
realis.) 



Streamers, Auroral A term some- 
times applied to the flashing columns or pillars 
of light that are thrown out in the shape of 
streams, from portions of the sky during the 
prevalence of an aurora. (See Aurora Bo- 
realis) 

Streaming Discharge. — (See Discharge, 
Streaming) 



Streamlets, Current 



-A theoretical 



conception of a series of parallel current 
streams or current filaments,- flowing through 
a solid conductor. 

In the case of uniform distribution of an elec- 
tric current where the current density is the same 
for all areas of cross-section, these current stream- 
lets are all of the same strength. 

In the case of rapidly alternating currents, 
however, the current streamlets are of greater 
strength near the surface. When the rate of al- 
ternation is sufficiently great, they are almost 
entirely absent at the central parts. 

The conception of current streamlets is made 
in order to account for the increase in the resist- 
ance of a solid conductor through which rapidly 
alternating currents of electricity are passing. 
(See Currents, Si?nple-Periodic.) 

Streams, Convection Streams of 

electrified air or other gaseous or vaporous 
particles given off from the pointed ends of 
charged, insulated conductors. (See Con- 
vection, Electric) 

Street Mains. — (See Main, Street.) 

Street Service. — (See Service, Street) 

Strength, Field The intensity or 

total flux of magnetism of a dynamo. 

This term is also sometimes roughly used f r 
the current strength in the field magnet circuit of 
a dynamo-electric machine. 

Strength of Current.— (See Current 
Strength) 

Strength of Magnetic Field. — (See Field, 
Magnetic, Strength of) 

Strength of Magnetism. — (See Magnetism, 
Strength of.) 

Stress. — The pressure, pull, or other force 
producing a deformation or strain. 



Str. 



494 



[Sub. 



Stress, Dielectric The force pro- 
ducing the deformation or strain in a dielec- 
tric. 

A dielectric strain, in the case of a Leyden jar 
or condenser, is sometimes sufficiently great to 
pierce the dielectric. 

Stress, Electro-Magnetic The force 

or pressure in a magnetic field, which produces 
a strain or deformation in a piece of glass or 
other similar substance placed therein. (See 
Strain, Optical Electro-Magnetic?) 

Stress, Electrostatic The force or 

pressure in an electrostatic field, which pro- 
duces strain or deformation in a piece of glass 
or other substance placed therein. (See 
Strain, Electrostatic, Optical?) 

Stress, Energy of A term some- 
times used in place of potential energy. (See 
Energy, Potential?) 

Stress, Magnetic The force acting 

to produce a strain in the air-gap between 
two dissimilar magnet poles by the action of 
the lines of magnetic force, bridging such air 
gap. 

Striae, Electric Parallel streaked 

bands, consisting of alternate light and dark 
spaces, produced in tubes containing low 
vacua, by the passage of rapidly alternating 
currents through them. (See Tube, Strati- 
fication?) 

Strip, Safety — A strip or bar used as 

a safety fuse. (See Fuse, Safety?) 

Stripping. — Dissolving the metal coating 
from a silver-plated or other metal-plated ar- 
ticle. 

The object of the "stripping " process is tore- 
cover silver from imperfectly plated ware, or 
from old ware which is to be replated. 

Stripping of silver is accomplished either in the 
cold or by aid of heat, by the use of the following 
solutions, viz.: 
Concentrated sulphuric acid, 

(Baume, 66 degrees) ioo parts. 

Concentrated nitric acid, 

(Baume, 40 degrees) 10 " 

The objects are suspended in this liquid, which, 
provided it be not diluted with water, possesses 
the property of dissolving the silver without 
touching the metal underneath. 



Stripping Baths.— (See Bath, Strip- 
ping.) 

Stripping Liquid. — (See Liquid, Strip- 
ping.) 

Stroke, Lightning — A disruptive 

discharge between two oppositely charged 
clouds, or between a cloud and the earth. 
(See Discharge, Disruptive.) 

Stroke, Lightning, Back or Keturn 

— An electric shock, caused by an induced 
charge, produced by the discharge of a light- 
ning flash. 

The shock is not caused by the lightning flash 
itself, but by a charge which is induced in neigh- 
boring conductors by the discharge. These in- 
duced effects are, in fact, effects of electro-dy- 
namic induction. (See Induction, Electro-Dy- 
namic.) A similar effect may be noticed by 
standing near the conductor of a powerful electric 
machine, when shocks are felt at every discharge^ 

The effects of the return shock are sometimes 
quite severe. These effects are often experienced 
by sensitive people on the occurrence of a light- 
ning discharge at a considerable distance. 

In some instances the return stroke has been 
sufficiently intense to cause death. In general, 
however, the effects are much less severe than 
those of the direct lightning discharge. 

Struts for Telegraphic Poles. — Inclined 
wooden or iron poles, applied to telegraph 
poles in order to support the thrust or press- 
ure acting on them. (See Pole, Tele- 
graphic?) 

Sturgeon's or Barlow's Wheel. — A wheel 
capable of rotation on a horizontal axis, which, 
when placed between the poles of a magnet, 
rotates when a current is passed through it 
between the axis and the circumference. 

Sub-Aqueous Cable. — (See Cable, Sub- 
Aqueous?) 

Sub-Branch. — (See Branch, Sub.) 

Sub-Main. — (See Main, Sub) 

Submarine Boat. — (See Boat, Sub- 
marine, Electric?) 

Submarine Cable. — (See Cable, Sub- 
marine?) 

Submarine Mine. — (See Mine, Sub- 
marine?) 



Sub.] 



495 



[Sur. 



Submarine Telegraphy.— (See Teleg- 
raphy, Submarine.) 

Substance, Ferro-Magnetic — A 

term proposed in place of paramagnetic, for 
substances that are magnetic after the man- 
ner of iron. (See Paramagnetic?) 

Subterranean Mine. (See Mine, Sub- 
terranean.) 

Subway, Electric An accessible 

underground way or passage provided for the 
reception of electric wires or cables. 

Underground electric conductors, like all elec- 
tric conductors, are liable to faults, crosses, etc. 
Unless they are readily accessible, very serious 
loss and damage may occur before the fault is 
located and corrected. 

Sulphating. — A name applied to one of the 
sources of loss in the operation of a storage 
battery, by means of the formation of a coating 
of inert sulphate of lead on the battery plates. 

The addition of a solution of sulphate of soda 
to the sulphuric acid liquid is claimed to have the 
effect of decreasing the extent of the sulphating. 

Summer Lightning. — (See Lightning, 
Summer?) 

Sun Spots. — (See Spots, Sun.) 

Sunstroke, Electric, or Electric Prostra- 
tion or Insolation Physiological 

effects, similar to those produced by exposure 
to the sun, experienced by those exposed for 
a long while to the intense light and heat of 
the voltaic arc. 

Electric sunstroke is sometimes called electric 
insolation, or electric prostration. 

The effects of electric sunstroke were first 
noticed by Desprez in his classic experiments on 
the fusion or volatilization of carbon. 

On undue exposure to an intense electric light 
the eyes are irritated and the skin burned as 
by the sun. In some cases it is claimed that the 
effects of sunstroke, or excessive production of 
heat, as in true insolation, are produced. In the 
applications of electricity to electric furnaces, 
these same effects have been noticed in an inten- 
sified degree. 

From some recent investigations it would ap- 
pear that these effects are to be ascribed to the 
light rather than to the heat. 



The symptoms are as follows: Pain in the 
throat, face and temples, followed by a coppery 
red color of the skin, irritation and watering of 
the eyes, when the symptoms disappear. The 
skin peels off in about five days. 

Superficial Eddy Currents. — (See Cur- 
rents, Eddy, Superficial.) 

Super-Saturation of Solution. — (See 
Solution, Super-Saturation of.) 

Supplement of Angle. — (See Angle, Sup- 
plement of.) 

Supply, Unit of, Electrical A unit, 

provisionally adopted in England by the 
Board of Trade, equal to 1,000 amperes flow- 
ing for one hour under an electromotive force 
of one volt. 

This would, of course, equal 1,000 watt-hours, 
and would be the same as 100 amperes flowing 
for ten hours under one volt. 

One unit of electrical supply is equal to 1.34 
actual horse-power expended for one hour, and 
will feed 13.4 Swan lamps of 21 candle-power for 
one hour. It is equal in illuminating power in 
Swan lamps to the light produced by 100 cubic 
feet of gas consumed in twenty 14-candle burners 
in one hour. 

The unit of electrical supply is called a "Board 
of Trade unit," a B. O. T. unit, or simply a bot. 
It is equal to one kilo-watt hour. 

Support, Tripod Roof A support 

for a housetop telegraphic line. 

The tripod roof support, as its name indicates, 
consists of a three-legged support for any suitable 
insulator. 

A common form is shown in Fig. 516. 

Support, Underground Cable A 

support provided for holding a cable where 
it passes around the side of a man-hole, un- 
derground conduit, or other similar location. 

Surface, Demarcation — The surface 

at w T hich a demarcation current is generated. 

The surface which marks the point of in- 
jury in a muscle or nerve. 

Demarcation currents in electro-therapeutics, 
are currents produced in injured nerves or 
muscles. They are probably due to the chemical 
changes that take place between the injured and 
the uninjured tissues. The demarcation surface is 



Sur.] 



496 



[Sur. 



the surface separating parts in a normal condi- 
tion from those in an abnormal condition. 

An injury to a muscle or nerve causes or pro- 
duces at such surface a dying substance which is 




Fig. Si 6. Tripod Roof Support. 

negative to the uninjured, normal or positive sub- 
stance. Such a surface results in a demarcation 
current. 

Surface Density. — (See Density, Surface.) 

Surface, Equipotential, of a Conductor 
Through Which a Current is Flowing- 

— A surface described within the mass of a 
conductor, conveying an electric current, at 
points perpendicular to the direction of the 
flow, all possessing the same potential. 

Surface, Equipotential, or Level Surface 
of Escaping Fluid A surface de- 
scribed within the mass of a fluid in motion 
at all places perpendicular to the stream lines 
passing such surface. 

Surface Integral of Magnetic Induction. 
— (See Induction, Magnetic, Surface-Inte- 
gral of.) 

Surfaces, Equipotential, Electrostatic 

Surfaces, all the points of which are 

at the same electric potential. (See Poten- 
tial, Electric?) 



Electric surfaces perpendicular to the lines 
of electric force over which a quantity of 
electricity, considered as being concentrated 
at a point, may be moved without doing 
work. (See Field, Electrostatic.) 

Equipotential surfaces correspond with a water 
level, over which a body may be moved horizon- 
tally without doing any work against the force of 
gravity. 

In the case of the charged insulated sphere, 
shown in Fig. 517, the equipotential surfaces, 
represented by the circles, are concentric. 




Fig. 5 1 y. Equipotential Surfaces. 

Surfaces, Equipotential, Magnetic 

— Surfaces surrounding the poles of a mag- 
net, or system of magnets, where the mag- 
netic potential is the same. (See Potential, 
Magnetic?) 

Magnetic equipotential surfaces extend in a 
direction perpendicular to the lines of magnetic 
force. (See Field, Magnetic.) 

No work is required in order to move a unit 
pole over equipotential magnetic surfaces, be- 
cause in so doing it cuts no lines of magnetic 
force. Work, however, is done when the motion 
is from one equal potential surface to another. 

Equipotential surfaces, whether electric or mag- 
netic, cannot intersect orie another, since their 
potential is the same at all points. 

Surfaces, Isothermal Surfaces con- 
necting points in a body which have the same 
temperature. 

Surging Discharge. — (See Discharge, 
Surging) 

Surgings, Electric Electric oscilla- 
tions set up in a charged conductor that is 
undergoing rapid discharge. 

These surgings produce waves in the surround- 
ing ether that travel outwards with the velocity of 



Sus.] 



497 



[Sus. 



light. {See Electricity, Hertz's Theory of Elec- 
tro-Magnetic Radiations or Waves.) 

Susceptibility, Magnetic The ratio 

existing between the induced magnetization 
and the magnetic force producing such mag- 
netism, or the intensity of magnetism divided 
by the magnetic force. 

Susceptibility relates to the poles produced in a 
body by a magnetizing force, whereas permea- 
bility refers its power to conduct lines of force. 
When the inducing field has unit strength of 
magnetization, the magnetic susceptibility will 
measure directly the strength of the magnetiza- 
tion. 

When a bar of iron is placed in a magnetic 
field, it is threaded by the lines of magnetic force, 
and thus becomes magnetized by induction. This 
induction will necessarily depend both on the 
number of lines of force in the magnetizing field 
and on the magnetic permeability of the magnet- 
ized body ; or, in other words, the induction is 
equal to the product of the intensity of the mag- 
netizing field and the magnetic permeability of 
the body in which the induction occurs. 

The magnetic susceptibility is sometimes called 
the Co-efficient of Magnetization; calling K, the 
susceptibility, H, the magnetizing force, and I, the 
intensity of the resulting magnetization; then 

K=i. 
H 

The magnetic permeability is sometimes called 

the Co-efficient of Magnetic Induction, calling ju, 

the permeability, B, the magnetic induction and 

H, the magnetic force producing the induction ; 



then 



M = 



B 



Suspending Wire of Aerial Cable. — (See 
Wire, Suspending, of Aerial Cable) 



— The suspen- 



Suspension, Bifilar - 

sion of a needle by two 
parallel wires or fibres, 
as distinguished from 
a suspension by a sin- 
gle wire or fibre. 

M 

A bifilar suspension is - 

shown in Fig. 518. The 

two threads, a b and a' c 

b', are connected to the Fig. 5 18. Bifilar Suspen- 

needle M N, so as to per- slon ' 

mit it to hang in a true horizontal position. Any 



tU^ 



twisting, around the imaginary axis c c', causes 
the lines of suspension, ab and a' b', to tend to 
cross one another and so shorten the axis c c'. 

Harris, who was the first to employ the bifilar 
suspension, showed that the reactive force im- 
parted to the suspension threads by turning the 
needle, was: 

(1.) Directly proportional to the distance be- 
tween the threads. 

(2.) Inversely as their lengths. 

(3.) Directly proportional to the weight of the 
suspended body. 

(4.) Proportional to the angle of twist or torsion 
of the threads on each other. 

Any deflection of the needle shortens the verti- 
cal distance between the points of support and 
the needle, and so tends to lift the needle. The 
motions are therefore balanced against the force 
of gravity instead of against the torsion of the 
fibre. 

Suspension, Combined Fibre and Spring- 

— The suspension of a needle by the 

combined use of a spiral spring and a single 
fibre. 

In this form of suspension the spring is intro- 
duced between the fibre and the needle. It is 
valuable for marine galvanometers and other ap- 
paratus exposed to tilting or rolling motions, be- 
cause it permits the instrument to be tilted 
through several degrees without causing any con- 
siderable variation in the deflections produced by 
the current or the charge. 

Suspension, Fibre Suspension of a 

needle by means of a fibre of unspun silk or 
other material. 

A fibre suspension generally means a single 
fibre or thread. It may, however, be applied to 
a bifilar suspension. (See Suspension, Bifilar.) 

A fibre suspension is to be preferred to a. pivot 
suspension, since it eliminates all friction . It has, 
however, the disadvantage of necessitating level- 
ing screws. 

Suspension, Knife-Edge —The sus- 
pension of a needle on knife edges that are 
supported on steel or agate planes. 

A suspension of this kind is used in the dip- 
ping needle, since it permits of freedom of mo- 
tion in a single vertical plane only. 

Suspension, Pivot Suspension of a 

needle by means of a jeweled cup and a me- 
tallic pivot. 



Swa.J 



498 



[Swi. 



The jeweled cup is placed above the centre of 
gravity of the needle, and is supported on a steel 
point. As a rule, compass needles have this 
variety of support. 

Swage. — A particular form of anvil on 
which highly heated metallic plates are shaped 
by hammering them into forms the same as 
that of the anvil on which they are placed. 

Swage. — To fashion heated metallic plates 
by hammering them into the form of an anvil 
on which they are supported. 

Swaging. — Fashioning highly heated me- 
tallic plates into any desired form by ham- 
mering while on suitable dies. 

Swaging, Electric The forming or 

shaping of metallic plates by hammering 
them against suitable anvils or dies while 
softened by electrical heating. 

The electro-swaging apparatus consists of a 
welding transformer provided with a movable 
clamp. The pressure required for the swaging 
is attained by the use of steam admitted into a 
cylinder by a lever which operates a four-way 
valve. 

The rod, bar, or plate of metal to be shaped or 
swaged, is first heated by the passage of a pow- 
erful heating current, obtained preferably from a 
welding transformer, one of the clamps of which 
is movable. When the metal is suitably softened 
by the passage of the current, it is then subjected 
to swaging. 

Swelling Current. — (See Currents, Swell- 
ing^ 

Swelling Faradic Current. — (See Cur- 
rents, Swelling Faradic?) 

Swinging Annunciator. — (See Annuncia- 
tor, Pendulum or Swinging?) 

Swinging Cross. — (See Cross, Swinging 
or Intermittent?) 

Switch, Automatic, for Incandescent 

Electric Lamps A device by which 

incandescent electric lamps can be lighted or 
extinguished at a distance by means of push 
buttons. 

The automatic switch for incandescent lamps 
corresponds in electric lighting to the automatic 
gaslighting device in systems of electric gaslight- 
ing. It consists essentially of two electro- 
magnets, one for turning the switch which lights 



the lamp by cutting them into the circuit of the 
lighting mains or conductors, and the other for 
extinguishing them, by cutting them out. These 
electro-magnets are operated by two push buttons, 
a black one to extinguish the lamp and a white 
button to light it. 

The details of the automatic switch are shown in 
Fig. 520. ThemainsM 1 andM 2 , areconnected to 
one set of contacts, and the branches containing 




Fig* 5*9- Automatic Switch. 
the lamps to be lighted, to the contacts between 
them. The push buttons, P 1 and P 2 , are con- 
nected by their wires to the main M 1 and the 
branch B 1 . 

These buttons are made respectively positive 
and negative, and are marked -f- and — . The 
third wire of the push button is connected as 
shown to the lamp L, and the switch magnet, 
SM. 

When the contact is closed atP 1 , the arma- 
ture of S M, closes the contact through C. 
When the button is released, connection is estab- 




Fig. J 20. Automatic Switch. 

lished between the magnet and the lamp L, in 
series. This is for the purpose of cutting down 
the circuit to the -^ of an ampere, and thus per- 
mitting a thin wire to serve between the button 
and the switch magnet. 

When the button, P 2 , is closed the lamps are 
turned out. 

Switch Board. — (See Board, Switch?) 

Switch Board, Multiple —(See 

Board, Multiple Switch?) 



SwL] 



499 



[Swi. 



-(See 



-(See 



Switch Board, Telegraphic — 

Board, Switch, Telegraphic?) 

Switch Board, Trunking — 

Board, Switch, Tr unking?) 

Switch, Break-Down A special 

switch, employed in small three-wire systems, 
for connecting the positive and negative bus- 
wires in such a manner as to practically 
convert it into a two-wire system and permit 
the system to be supplied with current from 
a single dynamo. (See Wires, Bus.) 

Switch, Changing A switch de- 
signed to throw a circuit from one electric 
source to another. 

A changing switch, for example, is of use in 
disconnecting a circuit from one dynamo and 
connecting it to another; or, in other words, to 
suddenly transfer the load from one dynamo to 
another. 

Switch, Changing-Over — A term 

sometimes applied to a changing switch. 
(See Switch, Changing.) 

Switch, Distributing A multiple 

switch board. (See Board, Multiple Switch) 

Switch, Distributing, for Electric 

Lights A switch employed in a 

system of arc lighting by series-distribu- 
tion, by means of which any particular 
dynamo-electric machine or a number of 




Fig.j2r. Double- Break Knife Switch. 

separate dynamo-electric machines can 
be connected with the same circuit without 
interfering with the lights. (See Board, Mul- 
tiple Switch?) 

Switch, Double-Break — A term 

sometimes used for double-pole switch. (See 
Switch. Double-Pole? 



Switch, Double-Break Knife — A 

knife switch provided with double-break con- 
tacts. 

A double-break knife switch is shown in Fig. 
521. 

Switch, Double-Pole —A switch 

that makes or breaks contact with both poles 
of the circuit in which it is placed. 

A switch consisting of a combination of 
two separate switches, one connected to the 
positive lead and the other to the negative 
lead. 

Double-pole switches are used in most systems 
of incandescent lighting in order to insure the 
thorough separation of the circuit from the main 
conductor or leads when cut out and to diminish 
the spark. 

Switch, Feeder The switch em- 
ployed for connecting or disconnecting each 
conductor of a feeder from the bus-bars in a 
central station. 

Switch, Four-Point A switch by 

which a circuit can be completed through 
four central points. 

Switch, Knife A switch which is 

opened or closed by the motion of a knife 




Fig. 522. Lamp- Socket Switch. 

contact which moves between parallel contact 
plates. 

A knife-edge switch. (See Switch, Knife- 
Edge.) 

Switch, Knife-Break — A knife 

switch. (See Switch, Knife.) 

Switch, Knife-Edge A term some- 
times used in place of knife switch. (See 
Switch, Knife.) 



Swi.] 



500 



[Swi. 



Switch, Lamp-Socket — A switch 

placed in the socket of an incandescent lamp 
and provided for throwing the lamp in and 
out of the circuit. 

A form of lamp socket switch is shown in Fig. 
522. Its operation will be understood from an 
inspection of the drawing. 

Switch Pin. — (See Pin, Switch?) 

Switch, Plug A switch in which a 

metal plug is withdrawn to throw into a cir- 
cuit a coil or other device, the ends of which 
are connected to metallic blocks that are suf- 
ficiently near together to be joined and short- 
circuited by the insertion of the plug. 

Switch, Pole-Changing A switch 

employed for changing the direction of the 
current in any circuit. 

A form of pole-changing switch is shown in Fig. 
523. 




Fig. 523. Pole- Changing Switch. 

If the two outer contacts are connected to the 
same pole as the source, as, for example, the 
positive, and the two intermediate contacts are 
connected to the other pole, or to the negative, 
then in the position shown in the cut, the current 
will flow through any receptive device connected 
with the switch, in one direction, but if the 
switch is moved to the left, it will flow in the op- 
posite direction. 

Switch, Removable Key A plug 

switch. (See Switch, Plug.) 

Switch, Reversing A switch for 

reversing the direction of the battery current 
through a galvanometer. 

A simple reversing switch consists of four in- 
sulated brass segments mounted on a plate of 
ebonite and furnished with openings between 
them for plug connections. 

The battery terminals are connected to two di- 
agonally opposite segments, as B, and D, Fig. 
524, and the leading wires of the galvanometer, 



or other instrument, to the other segments, as C 
and A. If, now, the plugs are placed between B 
and C, and A and D, the battery current flows 
in one direction. If, however, the plugs are 




Fig. 524. Reversing Switch. 

placed between A and B, and C and D, the bat- 
tery current will flow in the opposite direction. 

The battery current is cut off if one plug is re- 
moved. In practice, however, it is preferable to 
remove both plugs, so as to avoid any current 
from want of sufficient insulation. 



Switch, Snap 



-A switch in which 



the transfer of the contact points from one 
position to another is accomplished by means 
of a quick motion obtained by the operation 
of a spring. 

The object of the snap switch is to prevent the 
switch resting in any half way position, and thus 
preventing the establishing of an arc. 

Switch, Telephone, Automatic A 

device for automatically transferring the con- 
nection of the main line from the call bell to 
the telephone circuit. 

In most telephone circuits, as now arranged, 
the automatic switch, besides transferring the main 
line from the call bell to the telephone circuit, 




Fig. 52J. Automatic Telephone Switch. 

closes the local battery circuit of the transmitter 
on the removal of the telephone from its support- 
ing hook. 



Swi.] 



501 



[Sym. 



The means whereby this is accomplished are 
shown in Fig. 525. On the removal of the tele- 
phone from the hook L, the lever is pulled up- 
wards by the spring Z, thus closing the contacts 1, 
2 and 3, by which the local battery S, is closed 
through the circuit of the transmitter, the tele- 
phone disconnected from the circuit of the call bell 
M, B, and connected with the circuit of the trans- 
mitter. On replacing the telephone on the hook 
L, its weight depresses the lever, breaking con- 
nection with 1, 2 and 3, and establishing connec- 
tion with the call circuit. 

Switch, Three-Point A switch by 

means of which a circuit can be completed 
through three different contact points. 

Switch, Time An automatic switch 

in which a predetermined time is required 
either to insert a resistance in or remove it 
from a circuit. 

Switch, Two-Point A switch by 



means of which a circuit can be completed 
through two different contact points. 

Switch, Two- Way A switch pro- 
vided with two contacts connected with two 
separate and distinct circuits. 

Switch, Yale-Lock, for Burglar Alarm 

(See Alarm, Yale-Lock Switch 

Burglar?) 

Switchecl-In. — Placed in a circuit by means 
of a switch. (See Closed-Circuited?) 

Switched-Ont. — Cut out of a circuit by 
means of a switch. (See Ope?i-Circuited.) 

Symbols and Diagrams, Standard Elec- 
tric Standard symbols and diagrams 

used in electro-technics. 

The standard electric diagrams and symbols 
shown on pages 501, and 502, were arranged by 
Prof. F. B. Crocker, and are reproduced from 
the Electrical Engineer. 



SYMBOLS COMMONLY USED IN ELECTRICAL WORK. 



MECHANICAL. 



ELECTRICAL. 



L or 1. Length 
JHorm. Mass 
Tart. Time 
v. Velocity 
Fort. Force 
g. Acceleration 

due to gravity. 
Yforyr. Work. 
P. Power. 
ft. lb. Footpound. 



E. 07-E.M.F. Electromotive 

force 
P.D. Potential difference 
C. Current 
R. Resistance 
p. Specific resistance 
Q. Quantity 
K. Electrostatic capacity. 



D. Diameter 

r. Radius 

H.P. Horse power 

I.H.P. Indicated " 

B.H.P. Brake 

r.p.m. Revolutions 

per min. 
C.G.S. Centimetre 

gramme second L Inductance {Coeffic. of) 
{System) M 

» w n a ■ A-.BI. Amperemeter. 

A.W.G. American 

Wire Gauge ▼•*■ Voltmeter 
B.W.G.Birming/iam FM - Field Magnet 

Wire Gauge -f- Positive pole or terminal 
— Negative " " " 



Y. Volt 
amp. Ampere 



ta. Ohm m 

D,. Megohm. H 

B.A.U. Brit. Ass'n Unit 



mfd. Microfarad 
h. or hy. Henry 
z. Electrochejnical 

equivalent 
J. Joule 
K.W. Kilowatt 

Complete period 

{Alt. CUr-.) 

"D_ Dynamo 
-l|lr Battery 



MAGNETIC. 

North pole 

South pole 
, Strength of pole 

Magnetizing f 01 ce 
{C.G.S.) 

Magnetic induction 

{C.G.S. lines) 
Intensity of mag 
netization 

Magnetic per- 
meability 

Magnetic sus- 
ceptibility 

Horizontal 

intensity of Earth 's 

magnetism 



Compound Wound Dynamo Siemens I Armai 




If 



r J . 



Jlmmeter orVbUmcier 





Telephone Cimdt 



-to 



Alternating Current 
Transformer Diagram 
I Primary E M ' F 
n Primary Current 
\H Secondary £ ^t~P I 



tnamaescent Lighting 
System, 




Sym.J 



503 



tSym. 



jvtorse Telegraph System 
1 




^rctamp 



Fig, 526. Crocker's Chart of Standard Electric Symbols and Diagrams. 



Sym.] 



503 



[Sys. 



Symmetrical Induction of Armature. — 

(Set Induction, Symmetrical, of Ar -matter e.) 
Symmetrical Magnetic Field. — (See 

Field, Magnetic, Symmetrical.) 

Sympathetic Electrical Yibratious. — 

(See Vibrations, Sympathetic Electrical.) 

Sympathetic Yibratious.— (See Vibra- 
tions, Sympathetic.) 

Synchronism. — The simultaneous occur- 
rence of any two events. 

A rotating cylinder, or the movement of an 
index or trailing arm, is brought into synchronism 
with another rotating cylinder or another index 
or trailing arm, not only when the two are mov- 
ing with exactly the same speed, but when in ad- 
dition they are simultaneously moving over simi- 
lar portions of their respective paths. 

In the Breguet Step-by-Step or Dial Telegraph 
(See Telegraphy, Step-by-Step), the movements of 
the needle on the indicator are synchronized with 
the movements of the needle on the manipulator. 
In systems oiPac-Simile Telegraphy the move- 
ments of the transmitting apparatus are syn- 
chronized with those of the receiving apparatus. 

In Delany's Synchronous Multiplex Telegraph 
System, the trailing arm that moves over a cir- 
cular table of contacts at the transmitting end, 
is accurately synchronized with a similar trailing 
arm moving over a similar table at the receiving 
end. 

Delany, who was the first to obtain rigorous 
synchronism at the two ends of a telegraphic 
line hundreds of miles in length, accomplishes 
this by the use of La Cour's phonic wheel, 
through the agency of correcting electric im- 
pulses, automatically sent in either direction over 
the main line, when one trailing arm gets a short 
distance in advance or back of the other. 

With alternating current dynamos, where one 
dynamo is feeding incandescent lamps connected 
to the leads in multiple, and it is desired to 
couple another alternating current dynamo in 
parallel with the first, it is necessary to obtain a 
complete synchronism of the two dynamos before 
coupling them, since otherwise the lamps will 
show variations in their light, and the machine 
may suffer. 

Synchronizable. — Capable of being syn- 
chronized. (See Synchronism.) 

Synchronize. — To cause to occur or act 
simultaneously. (See Synchronism.) 



Synchronized. — Caused to occur or act 

simultaneously. (See Synchronism.) 

Synchronizing- Dynamo-Electric Ma- 
chine. — (See Machine, Dynamo-Electric, 
Synch ronizing.) 

Synchronous Multiplex Telegraphy. — 

(See Telegraphy, Synchronous Multiplex, 
Delany s System?) 

System, Astatic An astatic com- 
bination of magnets. 

An astatic needle consists of an astatic system 
of two magnetic needles. The needles are 
rigidly fixed together with their opposite poles 
facing each other. The two needles form an as- 
tatic pair or couple. (See Needle, Astatic.) 

System, Block, for Railways (See 

Railroads, Block System for?) 
System, Centimetre - Gramme - Second 

(See Units, Ce?itimetre - Gra?nme - 



Second?) 

System, Continuous Underground, of 
Motive Power for Electric Railroads 

— (See Railroads, Electric, Continuous Un- 
derground Sy stein of Motive Power for?) 

System, Dependent, of Motive Power for 

Electric Railroads (See Railroads, 

Electric, Dependent System of Motive 
Power for?) 

System, Independent, of Motive Power 
for Railroads (See Railroads, Elec- 
tric, Indepejident System of Motive Power 
for.) 

System, Multiphase A term fre- 
quently applied to a system of rotating elec- 
tric currents. (See Current, Rotating.) 

System of Distribution of Electricity by 
Commutating Transformers. — (See Elec- 
tricity, Distribution of, by Commutating 
Transforiners.) 

System of Distribution of Electricity by 
Condensers. — (See Electricity, Distribution 
of, by Altertiating Currents by Means of 
Condensers. Electricity, Distribution of, by 
Contitiuous Current by Means of Co?idens- 
ers.) 

System of Distribution of Electricity by 
Means of Alternating Currents.— (See Elec- 



SysJ 



504 



[Tai. 



tricity, Distribution of, by Alternating Cur- 
rents.) 

System of Distribution of Electricity by 
Motor Generators. — (See Electricity, Dis- 
tribution of, by Motor Generators?) 

System, Three-Wire A system of 

electric distribution for lamps or other trans- 
lating devices connected in multiple, in which 
three wires are used instead of the two usually 
employed. 

In the three-wire system two dynamos are gen- 
erally employed, which are connected with one 
another in series. 

The three conductors are connected as shown 
in Fig. 527, the central conductor to the junction 
of the two dynamos and the two others to their 
free terminals, and the difference of potential be- 
tween the central and the two outer conductors 
is maintained the same. The lamps, or other 
electro-receptive devices, are placed in multiple- 
arc between either branch, and so distributed 
that the current in each branch is the same. 
When such balance is established no current 
flows through the central or neutral conductor. 
But when that balance is disturbed, the surplus 
current in one branch is taken up by the central 
conductor. 

The three-wire system effects considerable 



economy in the weight of wire required. Since in 
the multiple-series-connection of electro -receptive 
devices whatever difference of potential is im- 
pressed on the mains is fed to each device, no 
higher difference of potential can be employed on 
the mains than that which the devices are capa- 
ble of taking. In the case of an incandescent 
lamp, if such difference be exceeded, too strong 
a current is passed through the lamps with a 
consequent decrease in their life. 

In the three- wire system of distribution a higher 
difference of potential can be maintained on the 
mains than is required for any lamp placed in 



■G- 




O 



o 



<y 



Fig. S 27. Three-Wire System 

connection therewith, and in this manner a con- 
siderable saving is effected in the cot of the leads. 



T. — A symbol used for time. 

T-shaped Spark.— (See Spark, T-Shaped.) 

Table, Quadruplex, A-Side of — 

That side of a quadruplex system which is 
worked by means of reverse currents. (See 
Telegraphy, Quadruplex?) 

Table, Quadruplex, B-Side of 

That side of a quadruplex system which is 
worked by means of strengthened currents. 
(See Telegraphy, Quadruplex?) 

Tables of Conducting Powers. — (See 
Powers, Conducting, for Electricity. Re- 
sistance, Electric?) 

Tachograph. — An apparatus for recording 
the number of revolutions per minute of a 
shaft or machine. 



Tachometer. — An apparatus for indicating 
at any moment on a revolving dial the exact 
number of revolutions per minute of a shaft 
or machine. 

A tachometer is sometimes called a speed in- 
dicator. 

Tachyphore. — A term proposed by Wurtz 
for a system of electric transportation, in 
which a carriage, formed of magnetic ma- 
terial, is propelled by the sucking action of 
solenoids placed along the track and ener- 
gized in succession during the passage of the 
car. 

This is generally called the portelectric sys- 
tem. (See Portelectric.) 

Tail Light— (See Light, Tail) 



Tai.] 



505 



[Tas. 



Tailings. — False markings received in sys- 
tems of automatic telegraphy, due to retard- 
ation. (See Retardation) 

Tailing's. — A term applied to the current 
that runs out of a line at the receiving end. 

The current that continues to run out at 
the receiving end of the circuit after the send- 
ing current is broken. 

The tailings in a telegraphic line are due to the 
effects of self-induction and static capacity follow- 
ing the breaking of the circuit which produce a 
current in the same direction as that sent into the 
line. Consequently, on the breaking of the cir- 
cuit, the current continues to flow out of the line at 
the distant or receiving end. This prolongation 
of the original current is known technically as 
the tailing or the tailing current. 

Talk, Cross In telephony an indis- 
tinctness in the speech transmitted over any 
circuit, due to this circuit receiving, either by 
accidental contacts or by induction, the speech 
transmitted over neighboring circuits. 

Tangent.— One of the trigonometrical 
functions. (See Function, Trigonometrical '.) 

Tangent and Sine Galvanometer, Com- 
bined (See Galvanometer, Combined 

Tang e nt and Sine?) 

Tangent Galvanometer.— (See Galva- 
nometer, Tangent.) 

Tangent Scale.— (See Scale, Tangent.) 

Tangentially Laminated Armature Core. 

— (See Core, Armature, Ta?igentially Lam- 
inated) 

Tank, Cable A water-tight tank in 

which a section of a cable is placed for pur- 
poses of testing. 

The cable is tested either when merely covered 
by water, or when subjected to a pressure ap- 
proximately equal to or in excess of that to which 
it will be subjected when laid in the water. 

Reid has constructed cable tanks for testing 
under pressures as great as 4,500 pounds per 
square inch. The pressure is obtained by means 
of force pumps. 

When a cable section is subjected to these 
pressures any flaws or defects would be at once 
detected by the entrance of the water. 



Tanning, Electric An application 

of electric currents to tanning leather. 

The dressed hides are steeped in a solution of 
tannin through which an electric current is 
passed. 

It is claimed, that by this process, the hides 
are thoroughly tanned in from one to four days, 
in place of from four to twelve months, as re- 
quired by the ordinary process. 

The tanning solution is placed in a vat fur- 
nished with suitable electrodes and filled with the 
tanning liquid, and the articles to be tanned are 
placed between the electrodes and a motion of 
revolution given to the vat. By these means 
the time required for the completion of the pro- 
cess is considerably shorter than that required by 
the ordinary process. 

Tap. — A conductor attached to a larger 
conductor in a shunted circuit. 

Tap, Ampere A tap provided for 

carrying off a current of one ampere. 

Tap Wires.— (See Wires, Tap) 

Tape, Insulating — A ribbon of 

flexible material impregnated with kerite, 
okonite, rubber or other suitable insulating 
material, employed for insulating wires or 
electric conductors at joints, or other exposed 
places. 

Sometimes the tape is formed entirely of some 
or another the above named insulating materials. 

Taped Wire.— (See Wire, Taped) 

Tapper, Double-Key (See Key, 

Double Tapper) 

Target, Electric A target in which 

the point struck by the ball is automatically 
registered by means of electric devices. 

A variety of targets have been devised. Gen- 
erally, however, the target is divided into a num- 
ber of separate sections provided with circuits of 
wires, on the making or breaking of any of which, 
by the impact of the ball, the section struck is au- 
tomatically indicated on an electric annunciator. 
(See Annunciator, Electro-Magnetic.) 

Taste, Galvanic A sensation of taste 

produced when a voltaic current is passed 
through the tongue or in the neighborhood of 
the gustatory nerves, or nerves of taste. 



Tea.] 



506 



[TeL 



Teaser. — An electric current teaser. (See 
Teaser, Electric Current) 

Teaser, Electric Current A coil 

of. fine wire placed on the field magnets of a 
dynamo-electric machine, underneath the se- 
ries coil wound thereon, and connected as a 
shunt across the main circuit. 

The name teaser was applied by Brush to the 
coil of fine wire used as above described to main- 
tain constant electromotive force under variations 
of load. 

Technics, Electro The science 

which treats of the physical applications of 
electricity and the general principles applying 
thereto. 

Tee, Lead A tee-shaped lead tube 

provided for the purpose of taking a branch 
joint from a main cable to a service line. 

Tee, Split-Lead A tee-shaped lead 

tube that is split for readily covering a joint 
at a loop in a cable. 

Tel-Autograni. — The recorded message 
obtained by means of a tel-autograph. (See 
Tel-Autograph) 

Tel- Autograph. — A telegraphic system for 
the fac-simile reproduction of handwriting. 

Teleautograph. — An orthography some- 
times employed for tel-autograph. (See Tel- 
Autograph) 

Tele-Barometer, Electric An elec- 
tric recording barometer for indicating and 
recording barometric or other pressures at a 
distance. 

Telegrapher's Cramp. — (See Cramp, 
Telegrapher's) 

Telegraphic. — Pertaining to telegraphy. 

Telegraphic Alarm. — (See Alarm, Tele- 
graphic) 

Telegraphic Alphabet. — (See Alphabet, 
Telegraphic) 

Telegraphic Alphabet, Continental Code 

(See Alphabet, Telegraphic : I?iter- 

national Code) 

Telegraphic Alphabet, Morse's 

(See Alphabet, Telegraphic : Morse's) 



Arm. — (See Arm, Tele- 



Telegraphic 

graphic) 

Telegraphic 
Telegraphic) 

Telegraphic Cable.— (See Cable, Tele- 
graphic) 

Telegraphic 
graphic) 

Telegraphic 
cuit, Earth, Telegraphic) 
Telegraphic Embosser. 
Telegraphic) 

Telegraphic Fixtures. 
Telegraphic) 

Telegraphic Fixtures, House-Top 



Bracket. — (See Bracket, 

3 able.— (See Cable, Tele- 

Code. — (See Code, Tele- 

Earth-Circuit. — (See Cir- 

-(See Embosser, 

-(See Fixtures,, 



(See Fixtures, Telegraphic House-Top) 

Telegraphic Ground Circuit. — (See Cir- 
cuit, Ground, Telegraphic) 

Telegraphic Joints.— (See Joint, Tele- 
graphic or Telephonic) 

Telegraphic Key. — (See Key, Telegraph- 
ic) 

Telegraphic Line Circuit. — (See Circuit* 
Line, Telegraphic) 

Telegraphic Needle. — (See Needle, Tele- 
graphic) 

Telegraphic Paper Winder. — (See Wind- 
ers, Telegraphic Paper) 

Telegraphic Pocket Relay. — (See Relay, 
Pocket Telegraphic) 

Telegraphic Register. — (See Register, 
Telegraph ic) 

Telegraphic Switch Board. — (See Board, 
Switch, Telegraphic) 

Telegraphic Translate!*. — (See Trans- 
later, Telegraphic) 

Telegraphically. — In a telegraphic 
manner. 

Telegraphing. — Sending a communication 
by means of telegraphy. 

Telegraphy, Acoustic A non-re- 
cording system of telegraphic communica- 
tion, in which the dots and dashes of the 
Morse system, or the deflections of the needle 
in the needle system, are replaced by sounds 



Tel. 



507 



[Tel. 



that follow one another at intervals, that 
represent the dots and dashes, or the de- 
flections of the needle, and thereby the letters 
of the alphabet. 

Morse invented a sounder, for this purpose, 
which is used very generally. (See Sounder, 
Morse Telegraphic.) 

Steinheil and Bright each invented acoustic 
systems of telegraphy in which electro-magnetic 
bells are used. 

For' details of the apparatus and system see 
Telegraphy, Morse System of. 

Telegraphy, American System of 

A term sometimes applied to the Morse sys- 
tem of telegraphy. (See Telegraphy, Morse 
System of) 

Telegraphy and Telephony, Simultane- 
ous, Over a Single Wire Any system 

for simultaneous transmission of telegraphic 
and telephonic messages over a single wire. 

These systems are based, in general, on the 
fact that a gradual make-and-break in a tele- 
phone circuit fails to appreciably affect a tele- 
phone diaphragm. By the use of graduators the 
makes and breaks required for the transmission 
of the telegraphic dispatch are effected so grad- 
ually that they fail to appreciably influence the 
telephone diaphragm, and thus permit simultane- 
ous telegraphic and telephonic transmission over 
a single wire. (See Graduators.) 

Telegraphy, Autographic A name 

sometimes applied to fac-simile telegraphy. 
(See Telegraphy, Fac-Simile) 

Telegraphy, Automatic A system 

by means of which a telegraphic message is 
automatically transmitted by the motion of a 
previously perforated fillet of paper contain- 
ing perforations of the shape and order re- 
quired to form the message to be transmitted. 

The paper passes between two terminals of the 
main line, the circuit of which is completed when 
the terminals come into contact at the perforated 
parts, and is broken when separated by the 
unperforated parts of the paper. 

In the automatic telegraph some form of regis- 
tering apparatus is employed. 

In the Wheatstone system, the perforations 
mechanically control the movements of the levers 
which make contacts between the line and the 
battery. 



The advantage of automatic telegraphy arises 
from the fact that the rate of transmission or re- 
ception of signals does not depend on the expert- 
ness of the operators, and the messages may be 
perforated on the slips preparatory to transmis- 
sion. 

Type- printing telegraphs are often used for 
registering apparatus, in which case the im- 
pulses required for the transmission of the dif- 
ferent letters are automatically sent into the line 
by the depression of corresponding keys on a 
suitably arranged key-board. 

Telegraphy, Chemical A system 

by means of which the closings of the main- 
line-circuit, corresponding to the dots and 
dashes of the Morse alphabet, are recorded 
on a fillet of paper by the electrolytic action 
of the current on a chemical substance with 
which the paper fillet is impregnated. (See 
Recorder, Chemical, Bains) 

Telegraphy, Contraplex — Duplex 

telegraphy in which transmissions are simul- 
taneously made from opposite ends of the 
line. 

When the transmissions are simultaneously 
made from the same end of the line, the system is 
called diplex telegraphy. (See Telegraphy, Di- 
plex. ) 

Telegraphy, Dial A system of 

telegraphy in which the messages are received 
by the motions of a needle over a dial plate. 
(See Telegraphy, Step-by- Step) 

Telegraphy, Diplex A method of 

simultaneously sending two messages in the 
same direction over a single wire. 

Diplex telegraphy is to be distinguished from 
duplex telegraphy, where two messages are simul- 
taneously transmitted over a single wire in oppo- 
site directions. 



Telegraphy, Double-Needle 



-A sys- 



tem of needle telegraphy in which two sepa- 
rate and independently operated needles are 
employed. 

This system differs from the single-needle sys- 
tem only in the fact that two needles, entirely in- 
dependent of each other, are mounted side by side, 
on the same dial, so as to permit their simultane- 
ous operation by the right and left hand of the 



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operator. Each needle has therefore a separate 
wire. 

The increase in speed of signaling thus obtained 
is not, however, sufficiently great to balance the 
increased expense of construction. Single-needle 
instruments, therefore, are preferred to those 
with two needles. 

Telegraphy, Duplex, Bridge Method of 

-A system whereby two telegraphic 



messages can be simultaneously transmitted 
over a single wire in opposite directions. 

Various duplex telegraphs have been devised. 

The Bridge Duplex is shown in Fig. 528. The 
receiving relay is placed in the cross wire of a 
Wheatstone bridge. (See Bridge, Electric.) 




Fig. 528. Duplex Telegraphy, Bridge, Method. 

When the ends of this cross wire are at the 
same potential, whicn will occur when the resist- 
ances in the four arms are proportionately equal, 
no current passes. 

The battery is connected through the trans- 
mitter K, which is arranged so that the battery 
contact is made before the connection of the line 
to earth is broken, to H, where the circuits 
branch to form the arms of the bridge. Adjust- 
able resistances A, B, are placed in the two arms 
of the bridge. 

The line wire L, connected as shown, forms 
the third arm, and a rheostat or other adjustable 
resistance R, connected to a condenser C, as 
shown, forms the fourth arm. (See Rheostat.) 
The relay M, is placed in the cross wire of the 
bridge thus formed. Small resistances V, and 
W, are placed in the circuit of the battery to pre- 
vent injurious short circuiting. 

A similar disposition of apparatus is provided 
at the other end of the line. If, now, the four re- 
sistances at one end are suitably adjusted, the 
relay will not respond to the outgoing current ; 
but, since an earth circuit is employed, it will 



respond to the incoming current. The relay at 
either end, therefore, will only respond to signals 
from the other end. The operator may thus 
signal the distant station while, at the same time, 
his relay, not being affected by his sending, is in 
readiness to receive signals from the other end. 

Telegraphy, Duplex, Differential Method 

of A system of duplex telegraphy in 

which the coils of the receiving and transmit- 
ting instruments are differentially wound. 

A differential system of duplex telegraphy is 
shown in Fig. 529. The coils of the receiving 
and transmitting galvanometers at A and B, are 
differentially wound. One of the coils of A, is 
connected to that of B, through the line, as 
shown; and the other, in each to the rheostats 
at R, and R'. As these coils are differentially 
wound, when equal currents flow in opposite 
directions through either of the instruments at A 
B, no deflection of the galvanometer occurs. 

The battery at A, has its copper terminal, and 
that at B, its zinc terminal, connected to earth. 
When the keys at A and B, are depressed simul- 
taneously, the currents sent into the line flow in 
the same direction and strengthen each other. 

Suppose now that only the key at A, be de- 
pressed. The current divides equally between 
rheostat and line, the resistance e a b b a' e', r', 
being made equal to the resistance e c d R. 

This current passes through both coils of the 
instrument at A, and produces no deflection of 
the needle; but since it only passes through one 
coil at B, it deflects the galvanometer needle, and 
produces a signal. 

b b' 




Earth + 

Fig.j2Q. Duplex Telegraphy, Differenti.il Method. 

If the keys at A, and B, are simultaneously 
closed, the effect on the line is to add the current 
of the two batteries, but each rheostat circuit is 
traversed by its own battery current only. 

The line-connected coils of the ga'vanometer 
have, therefore, the stronger currents flowing 
through them, and the needles of both are moved, 
just as if, with a single battery discharging into 
the line, its resistance had been decreased. Each 



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sender's instrument is unaffected by the currents 
he sends into the line, and is, therefore, ready to 
be operated by the currents sent into the line by 
the sender at the other end of the line. 

The two currents in duplex telegraphy, there- 
fore, do not pass each other on the line; on the 
contrary, they are sent into the line in the same 
direction. 

Since, when either key is moving there is a 
small interval of tine when the circuit is broken 
for incoming currents, the keys are generally 
made so as to close the second contact before 
breaking the first. 

In order to avoid disturbing the balance on the 
introduction of the resistance of the batteries at A 
or B, on closing the circuits, an equal resistance 
is added at r and r', between the back stop and 
the earth. 

Since the proper operation of duplex telegraphy 
requires a balance in the resistance of the circuits 
of the differentially wound coils, a rheostat at R, 
and R', is necessary. 

Besides balancing the line for resistance, it is 
necessary to balance it for capacity*. A condenser 
is, therefore, necessary when the circuit exceeds 
in length about ioo miles, or has much cable or 
underground wire. 

Telegraphy, Fac-Simile A system 

whereby a fac-simile or copy of a chart, 
diagram, picture or signature is telegraphically 
transmitted from one station to another. 

Fac-simile telegraphy is sometimes called auto- 
graphic telegraphy, or pantelegraphy. 

Bakewell's fac-simile telegraph, which was one 
of the first devised, consists of two similar metal 
cylinders c, c', arranged at the two ends of a 
telegraph line L, at M and M', as shown in Fig. 
530. These cylinders are synchronously rotated 




Fig. jjo. Bakewell's Fac-Simile Telegraphy. 

and provided with metallic arms or tracers r, r', 
placed on a horizontal screw in the line circuit 
and moved laterally over the surface of the 
cylinder on its rotation. 

At the transmitting station the chart, writing, 



or other design is traced with varnish, or other 
non-conducting liquid, on the surface of the 
metallic cylinder, as at M, and a sheet of chemi- 
cally prepared paper, similar to that employed in 
the Bain chemical system is placed on the surface 
of the receiving cylinder at M'. (See Recorder \ 
Chemical, Bams. ) 

The two cylinders being synchronously rotated, 
the metallic tracer breaks the circuit in which it 
is placed when it moves over the non-conducting 
lines on the cylinder, and thus causes correspond- 
ing breaks in the otherwise continuous blue spiral 
line traced on the paper-covered surface of M'. 

The telegraph keys at R, R', are used for the 
purposes of ordinary telegraphic communication 
before or after the rec;>id is transmitted. 

Caselli's Pan- Telegraph is an improvement on 
Bakewell's Cop)i.,g Telegraph. Better methods 
are employed for maintaining the synchronism 
between the transmitting and receiving instru- 
ments, for which purpose a pendulum, vibrating 
between two electro-magnets, is employed. 

Telegraphy, Fire Alarm A system 

of telegraphy by means of which alarms can 
be sent to a central station, or to the fire 
engine houses in the district, from call boxes 
placed on the line. 

The alarms are generally sounded by an ap- 
paratus similar to a district call, so that the pull- 
ing back of a lever rotates a whell, by means of 
which successive makes and break? are produced, 
the number and sequence of which enable the 
receiving stations to locate the particular box 
from which the signal is sent. 

In the case of some buildings, the alarms are 
automatic, and either call for help from the 
central office, or for the watchman in the build- 
ing, or else turn on a series of water faucets or 
jets, in order to extinguish the fire. 1 1 these 
cases thermostats are used. (See Thermostat.) 

Telegraphy, Gray's Harmonic Multiple 

-A system for the simultaneous trans- 



mission of a number of separate and distinct 
musical notes over a single wire, which 
separate tones are utilized for the simultane- 
ous transmission of an equal number of tele- 
graphic messages. 

The separate tones are thrown into the lines 
by means of tuning forks automatically vibrated 
by electro-magnets. Th.se forks interrupt the 



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circuit of batteries connected with the main line 
at the sending end of the line. 

The composite tone thus formed, is separated 
into its component tones by receiving electro- 
magnets called harmonic receivers, the armature 
of each of which consists of a steel ribbon or 
plate tuned to one of the separate notes sent into 
the line. As the complex or undulatory current 
passes through the coils of each harmonic re- 
ceiver, that note only affects the particular arma- 
ture that vibrates in unison with its ribbon or 
reed. The operator, therefore, at this receiver 
is in communication only with the operator at 
the key of the circuit that is sending this par- 
ticular note into the line. The same is true of the 
other receivers. 

The Morse alphabet is used in this system, the 
dots and dashes being received as musical tones. 
In practice it was found that there was no diffi- 
culty in each operator recognizing the particular 
sound of his cwn instrument in receiving, although 
many instruments were in the same room. 

By a subsequent invention the signals received 
are converted into the regular Morse characters 
by means of an ingenious device. 

Telegraphy, Induction A system 

for telegraphing by induction between moving 
trains and fixed stations on a railroad, by 
means of impulses transmitted by induction 
between the car and a wire parallel with the 
track. 

Two systems of inductive telegraphy are in 
actual use, viz., 

(i.) The Static Induction system of W. W. 
Smith and Edison, and 

(2.) The Ctirrent ox Dynamic Induction system 
of Willoughby Smith and Lucius J. Phelps. 

In the System of Static Induction, one of the 
condensing surfaces which receives or produces 
the charge, consists of a wire placed on the road 
so as to come as near the top of the cars of the 
moving train as possible. The other condensing 
surface is composed of the metal roofs of the mov- 
ing cars. 

Each condensing surface is connected to suit ■ 
able instruments and batteries, and to the earth ; 
the line wire at the fixed station being connected 
to earth through a ground plate, and the metal 
roof of the cars to earth through the wheels and 
track. 

Under these circumstances variations in the 
charge of either of the condensing surfaces pro- 



duce inductive impulses that are received by the 
other surface as telegraphic signals. 

The Morse alphabet is employed, but in place 
of the ordinary receiver or sounder, a telephone 
is used. 

In the System of Current Induction, the line 
wire is placed near the track, so as to be parallel 
with a coil of insulated wire placed on the side of 
the car, and which receives the inductive impulses. 
The coil of wire on the train is connected with 
instruments and batteries, and forms a metallic 
circuit. The line wire is also connected with 
suitable batteries and receiving and transmitting 
instruments. 

An induction coil is generally employed, since 
the greater and more rapidly varying difference 
of potential of its secondary wire renders it better 
suited for producing effects of induction. A tele- 
phone is employed as a receiver, as in the system 
of static induction. The metallic car roof and 
the lower truss rods have been successfully used as 
the secondary conductor of the induction coil. 

The automatic make-and break used for operat- 
ing the induction ceil, causes the Morse characters 
employed in this system to be received in the 
receiving telephone as shrill buzzing sounds. 

The receiving telephones used on the trains 
have a resistance of about 1,000 ohms. 

Telegraphy, Induction, Current System 

of A system of induction telegraphy 

depending on current induction between a 
fixed circuit along the road, and a parallel 
circuit on the moving train. 

The circuit on the train generally consists of a 
coil of wire. (See Telegraphy, Induction.) 

Telegraphy, Induction, Dynamic System 

of A term sometimes used in place of 

a system of telegraphic current induction. 
(See Telegraphy, Induction.) 

Telegraphy, Induction, Static System of 

A system of inductive telegraphy de- 
pending on the static induction between the 
sending and receiving instrument. 

A fixed wire placed along the road so as to come 
near another wire or metallic surface on the mov- 
ing train, imparts to the latter a static charge, 
which is utilized for the transmission of dispatches. 
The metal roof of the car is generally used for the 
condensing surface receiving the charge. (See 
Telegraphy, Induction.) 



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Telegraphy, Machine < A term some- 
times applied instead of automatic telegraphy. 
.(See Telegraphy, Automatic) 

A system of telegraphy is properly called ma- 
chine telegraphy when both the transmission and 
the receiving of the telegraphic messages are ac- 
complished by machine, instead of by the hand, as 
usual. 

Telegraphy, Morse System of A 

system of telegraphy in which makes and 
breaks occurring at intervals corresponding 
to the dots and dashes of the Morse alphabet 
are received by an electro-magnetic sounder 
or receiver. 

A metallic lever A, Fig. 531, is supported on a 
pivot at G, between two set screws D, D, so as to 
have a slight movement in a vertical plane. This 
motion is limited in one direction by a stop at C, 
called the anvil or front contact, and in the other 
direction by a set screw F, which constitutes its 
back stop. 

The front stop C, is provided with a platinum 
contact or stud, which may be brought into 
contact with, or separated from, a similar stud 
placed directly opposite it. These contacts are 
connected to the ends of the circuit so that on 




Fig' S3 1 - Telegraphic Key. 

the movements of the key, by the hand of the 
operator placed on the insulated head B, the line 
is closed and broken in accordance with the dots 
and dashes of the Morse alphabet. A spring, the 
pressure of which is regulated by the screw F', is 
provided for the upward movement of the key. 
A switch H, is provided for closing the line when 
the key is not in use. 

The system generally used in the United States 
is known as the " Closed- Circuit System," the bat- 
tery being connected to line whether the line is in 
use or not. This battery is generally placed at 
both ends of the line. 

In Europe, the " Open-Circuit System " is gen- 



erally used. Alternating currents and polarized 
relays are employed. One pole is connected to 
the line at the front of the key, and the other 
pole to the back of the key. When the line is 
not in use, it is connected to earth at both ends 
by switches conveniently placed for the operators. 
With this system, intermediate stations must each 
have a main battery, while in the closed-circuit 
system, the terminal batteries answer for all inter- 
mediate offices, which in some cases amount to as 
many as fifty. 

In the Morse system, each station is provided 
with a key, relay, sounder or register, and local 
battery. The closed-circuit, connecting one 
station with another, being broken by the open- 
ing of the switch H, or the working of the key, 
so as to open and close its contacts, the armature 
of the relay opens or closes the circuit of the 
local battery and operates the sounder or register- 
ing apparatus connected therewith. (See Sounder, 
Morse Telegraphic. Apparatus, Registering, 
Telegraphic.) 

Telegraphy, Multiplex A system 

of telegraphy for the simultaneous transmis- 
sion of more than four separate messages 
over a single wire. (See Telegraphy, Syn- 
chronous-Multiplex, Delanys System.) 

Telegraphy, Needle System of A 

system of telegraphy in which signals are 
transmitted by means of the movements of 
needles under the influence of the electric 
current. (See Telegraphy, Single-Needle) 

Telegraphy, Phonoplex A system 

of telegraphic transmission in which pulsatory 
currents, superposed on the ordinary Morse 
currents, actuate a modified telephonic re- 
ceiver, and thus permit the simultaneous 
transmission of several separate messages 
over a single wire without interference. 

Telegraphy, Printing A system of 

telegraphy in which the messages received 
are printed on a paper fillet. 

In Callahan's Printing Telegraph, two type 
wheels are employed, one of which carries letter 
type and the other numerals on its circumference. 
These printing wheels are placed alongside of 
each other, as shown in Fig. 532, but on separ- 
ate and independent axes. 

The type wheels are moved by a step-by-step 
device. The impulses necessary to bring the 



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desired letters in position for printing are auto- 
matically sent by a circuit maker and breaker. 
These impulses are sent into the line by the de- 
pression of keys on a suitably arranged key- 
board. 

When the proper letter or »tJ3x.eral is reached 
at the receiving end, the printing wheel is 
stopped, and a paper fillet is pressed against its 
surface. The printing wheel is kept covered 
with ink by means of an inked roller. 

The transmitting instrument is similar in its 
operation to the Breguet manipulator. Separate 
transmitters are used for each of the wires. (See 
Telegraphy , Step-by -Step.) 




Fig. S3 2 - Callahan' 's Printing Telegraph. 



■A system 



Telegraphy, Quadrupled — 

for the simultaneous transmission of four mes- 
sages over a single wire, two in one direction 
and the remaining two in the opposite direc- 
tion. 

Quadruplex telegraphy consists in fact of du- 
plex telegraphy duplexed. 

There are various systems of quadruplex teleg- 
raphy. The most important are the bridge 
method and the differential method. (See Teleg- 
raphy, Quadruplex, Bridge Method of. Telegra- 
phy, Quadruplex, Differential Method of.) 

Telegraphy, Quadruplex, Bridge Method 

of A system of quadruplex telegraphy 

by means of a double bridge duplex system. 
(See Telegraphy, Quadruplex?) 

In the bridge method of quadruplex telegraphy, 
as in the differential method, changes in the polar- 
ity and strength of the current are utilized to 
establish a double duplex system of transmission. 
Fig. 533 from Prescott's "Electricity and Electric 
Telegraphy, "from which the following desci iption 



is taken, shows tie method first employed by the 
Western Union Telegraph Company in 1874. 

A double current transmitter, or pole changer, 
is shown at T', with its operating key K' and 
local battery e'. This instrument interchanges 
the poles of the main battery E', when K, is de- 
pressed, and thus reverses the polarity of current 
on the line. 

The increment transmitter T 3 , is connected to 
the battery wire 12 of T', in such a way that 
when K', is depressed, the main battery E', is 
placed in series with battery E, of say twice ther 
strength of E', thus permitting a current of three- 
fold the original strength to be sent into the line. 




. 533. Quadruplex Telegraphy, Bridge Method. 



Two receiving instruments R' and R 2 , are 
placed at the distant end of the line. R', is a 
polarized relay whose armature is deflected in 
one direction by positive currents, and in the 
opposite direction by negative currents, independ- 
ently of their strength. That is to say, R', re- 
sponds to changes in the direction of the currents 
that pass through its coils, but not to changes in 
their strength. (See Relay, Polarized.) 

Relay R 2 , is non-polarized and the movements 
of its soft iron armature depend on a change in 
the strength of the current only. That is to say, 
R s , responds to changes in the strength of the 
current passing through its coils, but not to 
changes in their direction. 

These two relays R and R s , are placed in the 
bridge wire of a Wheatstone bridge. The entire 
apparatus of transmitting keys and relays is 
duplicated at each end of the line. Under these 
conditions, signals transmitted from either end of 
the line affect the instruments at the other end of 
the line, but not their own instruments, in the 
same manner as in the case of the bridge du- 
plex. (See Telegraphy , Duplex, Bridge Method 
of-) 

Telegraphy, Quadruplex, Differential 



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Method of A system of quadruplex 

telegraphy by means of a double differential 
duplex system. 

Quadruplex telegraphy depends for its opera- 
tion on the use of two differentially wound relays 
at each station. One of these relays A, as shown 
in Fig. 534, which shows the general arrangement 
of the system, gives signals on a change in the 
direction of the current, but none on a change in 
the current strength. The other B, gives signals 
on changes in current strength, but none on 
changes in direction. They are, therefore, in- 
dependent of each other, and operate sounders 
that are under the independent control of two 
distinct receiving operators. 

A table, divided into four sections, is provided 
with places for two sending and two receiving 
clerks. The name " A side " is given to the side 
worked by the reversed currents, and the "B 
side" to that worked by the strengthened cur- 
rents. 




REVERSING KE 

/ V E 

BATTERY 1, BATTERY 2. 

-Fig. 534. Quadruplex Telegraphy , Differential Method. 

Referring to Fig. 534 the reversing key on the 
*' A side " is merely indicated so as to avoid con- 
fusion by too great detail ; as is also the case with 
the increment key or the strengthening key atB. 
From the connections it will be seen that when 
the increment key is at rest, the reversing key 
sends currents from battery I. When the incre- 
ment key is depressed, the reversing key is shifted 
from battery I, and connected by its copper con- 
nection C, with the battery 2, of double the 
strength of I. Since, however, I, is thus connect- 
ed in series with C, the current strength is in- 
creased threefold. 

From the reversing key the current passes 
to the junction of the two coils with which the 
relay B, is differentially wound. It divides here 
between these coils, which are connected to simi- 



lar coils on relay A, as shown. The current 
from one coil on A, is sent to line, while that from 
the other coil goes to earth through the compen- 
sating rheostat. This arrangement forms a du- 
plex system, the outgoing currents of which have 
no effect on the home relays. 

Resistances R 2 and R 3 , are connected to the 
batteries I and 2, and the stops in the increment 
key in the manner shown, to the resistance of R 2 
and R 3 . The former is used in order to main- 
tain the resistance of the circuit, whether the bat- 
tery is in or out of circuit. The latter is called 
the spark coil, and is intended to decrease the 
sparking on closing circuit. 

When both are at rest, battery I, has its zinc 
connected to line through A, and its copper to 
earth through R 2 , CI, the lever of key B and 
key A, which last two are permanently connect- 
ed. A reversed or spacing current goes to line, 
without affecting the home relays, since it passes 
in opposite directions and with equal strength 
through differentially wound coils. 

When, however, the key A, is worked alone, 
it reverses the current and the signal is recorded 
by the distant relay A. 

If key B s is worked alone, it breaks connection 
with copper at the junction of the two battel ies, 
and makes contact with terminal copper of battery 
2, so as to send a zinc current of threefold strength. 
The distant relay B, records a signal because the 
current is now strong enough to move it. Relay 
A, however, is not affected, since the current has 
not been reversed. 

When both keys are simultaneously in action, 
then whenever B, is pressed, although the strength 
of A, may be increased, since its direction is not 
changed, the polarized tongue of its relay is un- 
affected by the movement of B, but any increase 
of current causes the armature of the distant re- 
lay of B, to move. 

This armature is held in position by springs of 
such a strength as to prevent its motion by a 
weak current, and being unpolarized, responds to 
either positive or negative cux-rents. It, there- 
fore, responds to B, and records a signal. When 
A, is pressed, it reverses the current, and conse- 
quently moves the distant relay A, but has no 
effect on B, since it causes no alternation in the 
strength of the current. 

The author has taken the above almost liter- 
ally fromCulley's " Handbook of Practical Teleg- 
raphy, " to which the reader is referred for a fuller 
description and details of apparatus. 



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Telegraphy, Simplex 



-A system of 



telegraphy in which a single message only 
can be sent over the line. 

Telegraphy, Single-Needle A sys- 
tem of telegraphy by means of which the 




Fig: SSS' Single- Needle Telegraphic Apparatus. 

signals transmitted are received by observing 
the movements of a vertical needle over a 
dial. 




of the observer represent the dashes, and move- 
ments to the left, the dots of the Morse alpha- 
bet. 

The single-needle apparatus of Wheatstone and 
Cooke's system is shown in Figs. 535, and 536. 
Fig. 535, shows the external appearance, and Fig. 




Fig. S3 6. Wheatstone and Cooke's Single- Needle Appa- 
ratus, Internal Arrangement. 

Movements of the top of the needle to the right 



Fig. 537. Wheatstone and Cooke's Single-Needle Ap-- 
paratus, External View. 

536, the internal arrangements as seen from the 
back. An astatic needle is placed inside two coils 
of insulated wire C C. Only 
one of these needles N, is vis- 
ible on the face of the receiving 
instrument. The current from 
the line enters at L, passes 
through the coil C C, and 
leaves at N. 

The movements of the needle 
to the right or the left are ob- 
tained by changing the direc- 
tion of the current in the coils 
C C. This is effected by work- 
ing the handle when sending, 
and thus moving the commuta- 
tor at S, S, and bringing the 
contact springs resting thereon 
into different contacts. 

In the more modern form of single-needle in- 
strument, shown in Fig. 537, a single magnetic 
needle N S, Fig. 538, only is placed in the 
coil. 

This needle is rigidly attached to a light needle 
a, b, used only as a pointer, and is alone visible 
in the front of the instrument. The relative dis- 
position of these needles is shown in Fig. 538. 

The reversals of the current, required to deflect 
the needle to the right or left, are obtained by 




Fig. 538. Needle 
and Pointer. 



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515 



[Tel, 




means of a double key or tapper, shown in Fig. 

539- 

The levers L and E, are connected respectively 
to line and earth, and, when not in use, rest against 
C, connected with the positive 
side of the battery; but when de- 
pressed connect with Z, attached 
to the negative side of the bat- 
tery. 

The depression of L, therefore, 
sends a negative current into the 
line and deflects the needle, say, 
to the left, while the depression 
of E, sends a positive current into 
the line and deflects the needle Fig. 53 g. Double 
to the right. The terms positive Key or Tapper. 
and negative currents are used in telegraphy to 
indicate currents whose direction is positive or 
negative. 

Telegraphy, Speaking- A system 

for the telegraphic transmission of articulate 
speech. (See Telephone.) 

Telegraphy, Step-by-Step A sys- 
tem of telegraphy in which the signals are 
registered by the movements of a needle over 
a dial on which the letters of the alphabet, 
etc., are marked. 

Dial telegraphs are especially employed for 
communication by those who are unable to readily 
read the Morse characters. 

The annexed instrument, devised by Breguet, 
was formerly used on some of the railway sys- 
tems of France. 

A needle advances over a dial by a step-by-step 




Fig. j 40. Step-by-Step Wheel. 

movement in one direction only. The alternate 
to-and-fro motions of the armature of an electro- 
magnet are employed to impart a step -by-step 
mot on to a peculiarly shaped toothed wheel 



T, T, Fig. 540, through the action of a horizontal 
arm c, attached thereto- and moving between the 
two prongs of a fork d, vibrating on a horizontal 
axis to which is attached a vertical pallet i. 

The receiving instrument is called the indicator, 
and consists of a needle attached to the axis of 
this wheel. The needle moves over the face of 




Fig. 541. Bregttet' s Indicator. 

the dial, shown in Fig. 541, on which are marked 
the letters of the alphabet and the numerals. 

The sending instrument is called the manipu- 
lator. It consists of a device for readily sending 
over the line the number of successive impulses 
required to move the needle step-by-step from 
any letter on the indicator t© which it may be 
pointing, to the next it is desired to send. 

The dial, shown in Fig. 542, is marked on its 
face with the same characters as the indicator. 
The edge of the wheel is provided with twenty- six 
notches in which a pin attached to a movable arm 
engages. The arm is jointed so that it can be 
placed in any of the notches on the face of the 
wheel. 




Fig. 542. Breguet's Manipulator. 

Below the dial face, and attached to the same 
axis as the movable arm, is a wheel provided 
with undulations consisting of thirteen elevations 
and thirteen depressions. 



Tel.] 



516 



[Tel. 



A lever T, pivoted at a, rests in these undu- 
lations at its upper end, and plays between two 
contact points at P and Q. 

If, now, the dials of the indicator and the man- 
ipulator both being at O, a movement is given to 
the arm by the handle M, to any point on the 
manipulator, there are thus produced the required 
number of makes and breaks to move the needle 
of the indicator to the corresponding letter or 
character. 

Telegraphy, Submarine A system 

of telegraphy in which the line wire consists 
of a submarine cable. 

In long submarine cables, in order to avoid 
retardation from the self-induction of the cur- 
rent, and the static charge arising from the cable 
acting as a condenser, very small currents are 
used. To detect these a very sensitive receiving 
instrument, such as the mirror galvanometer, or 
the siphon recorder, is employed. (See Galva- 
nometer, Mirror. Recorder, Siphon.) 

According to Culley, the retardation in the 
case of one of the submarine cables between 
Newfoundland and Ireland, amounts to two- 
tenths of a second before a signal sent from one end 
produces any appreciable effect at the other end, 
while three-tenths of a second are required for the 
current through the cable to gain its full strength. 

Telegraphy, Synchronous-M n 1 1 i p 1 e x, 

Delany's System A system devised 

by Delany for the simultaneous telegraphic 
transmission of a number of messages either 
all in the same direction, or part in one direc- 
tion and the remainder in the opposite direc- 
tion. 

The Delany system embraces the following 
parts : 

(I.) A circular table of alternately insulated 
and grounded contacts at either end of a tele- 
graphic line. 

(2.) A synchronized rotating arm or trailing 
contact, at each end ot the line, driven by a 
phonic wheel, and maintained in synchronous 
rotation by means of electric impulses automatic- 
ally sent out over the main line in either direc- 
tion, on the failure of the wheel at either end to 
rotate synchronously with that at the other end. 

(3.) Transmitting and receiving instruments 
connecting similar contacts at each end of the 
main line, and forming practically separate and 
independent lines for the simultaneous transmis- 



sion of dispatches over the main line in either 
direction. 

The main line is simultaneously connected at 
both of its ends to corresponding operating in- 
struments, and transferred from one set of instru- 
ments to another sc rapidly that the operators, 
either sending or receiving, cannot realize that 
the line has been disconnected from their instru- 
ments and given to others, because each of them 
will always have the line ready for use, even at 
the highest rate of manipulation, and will, there- 
fore, to all practical intents and purposes, have 
at his disposal a private wire between himself 
and the operator with whom he is in communica- 
tion. 

Therefore, although more than one operator 
may be spoken of as simultaneously using the 
line at any given time, yet in reality no two ope- 
rators are absolutely using it at the same time; 
but they follow one another at such short in- 
tervals, and the line is taken from one operator 
and transferred to another so rapidly, that none 
of them can at any time tell but that he has the 
line alone, and that therefore it is practically 
open for the use of every operator just as if he 
alone had control of it. 

There will, therefore, be established, by the 
use of a single line, as many private and separate 
lines as there are transferences of the line from 
the time it is taken from the first operator, and 
again given back to him. 

This system has been extended to as many as 
seventy-two distinct and separate printing cir- 
cuits, maintained and operated on a single con- 
necting line wire. 

The speed at which the circuits may be operated 
is in the inverse order of the number of circuits 
organized. The best results, practically, are 
obtained from six divisions of the contacts in the 
circle, which gives each operator about 36 con- 
tacts with the line per second, a speed which ad- 
mits of the highest rate of transmission on each of 
the six circuits. 

Fig. 543 shows the apparatus at each end of 
the line, at the stations X and Y. The apparatus 
at each end is substantially identical. A steel 
fork a, at each station, is automatically and con- 
tinuously vibrated by the action of the local bat- 
tery L, B, and the electro-magnet A, called the 
vibrator magnet. 

Platinum contacts x, x 1 , placed on the inner 
faces of the tines of the fork, make and break 
contact with delicate contact springs y, y 1 . 



Tel.] 



517 



[Tel. 



The fork being mechanically started into a 
vibratory motion, will automatically make and 
break its local circuit, and thus send impulses 
into the fork magnet A, that will continuously 
maintain the vibrations of the fork, in a well 
known manner. 

The making and breaking of the contacts x 
and y, consequent on the fork's vibration, open 
and close another local battery placed in a circuit 
called the motor circuit, in which is also placed an 
electro-magntt D, the functi >n of which is to 
maintain the continuous rotation of the trans- 
mission apparatus C. 



disc C, is rotated by the electro-magnet D, the 
trailing contact f, sweeps around the circular 




Fig. 343. Delany's Synchronous Mutiplex Telegraph. 

The continuous vibration of the fork makes and 
h>reaks the contacts at x and y, and thereby 
makes and breaks the motor circuit. The alter- 
nate magnetizations and demagnetizations of the 
cores of the motor-magnet D, cause the rotation 
of the transmission apparatus C. 

The motor magnet and transmission wheel or 
disc C, provided with projections c, c, is the in- 
vention of Paul La Cour, and is styled by him a 
"phonic wheel." 

The transmission apparatus is illustrated in de- 
tail in Figs. 544 and 545, and is an exact coun- 
terpart of the receiving apparatus at the other 
end of the line. A_ base plate E, provided with 




Fig. 344. The Phonic Wheel. 
binding posts, carries a vertical rotary shaft F. 
A circular table F 1 , is provided with a series of 
insulated contacts arranged symmetrically around 
the axis of rotation of the shaft. A radial arm F 2 , 
connected with the shaft F, carries at its outer 
extremity a trailing contact finger f. As the 




Fig- 34S- Th e Phonic Wheel. 
table F 1 , and is brought successively into contact 
with the insulated contact pieces placed on, the 
upper face of the table F 1 . 

The main line Q, Q, has one of its ends con- 
nected with the trailing finger f. As the shaft 
F, rotates, the line is therefore brought into suc- 
cessive electrical connection with the series of in- 
sulated contacts in the upper face of the table 
F 1 . 

Any suitable number of insulated contacts may 
be placed on the circular table F 1 ; sixty are 
shown in Fig. 546. In practice these contacts 
are connected in accordance with the number of 
circuits which it is desired to simultaneously 
maintain on the same wire. In the special case 
shown in the figure above referred to, it is ar- 
ranged so that four separate circuits shall be 
established on the same line wire. 

The sixty contacts are placed in six indepen- 
dent series, numbered from I to 10, consecu- 
tively. In the arrangement here shown two of 
the contact pieces in each series of ten are con- 
nected in the same circuit, and, as there are six 
series, each of the circuits so connected will have 
twelve contacts for each rotation of the disc, and 
twelve electrical impulses, as will be afterwards 
described. 

The detailed mechanism, by means of which 
the separate and independent circuits so obtained 
are utilized for the transmission and reception of 
messages, is shown in Fig. 546. R, R l , R 3 and 
R 3 , are polarized relays; S, S 1 , S 3 and S :J are 
ordinary Morse sounders, although in the practice 
of this invention some improvement has been in- 
troduced in connection with the receiving instru- 
ments. The connections with the main and the 
local batteries M B and L B, are clearly shown 
in the figure. 

It will be noticed that the relay R, is connected 



Tel.] 



518 



[Tel, 



with the wire r, and with the contacts I and 5 ; 
R 1 is connected by r 1 , with the contacts 2 and 6, 
R 2 , by the wire r a , with the contacts 3 and 7, 
and R 3 , by the wire r 3 , with the contacts 4 and 
8. Similar instruments and circuits are placed 
at each end of the line. 

Without further describing the operation of the 
instruments shown in the figure, it need only now 
be borne in mind that the corresponding relays at 
the distant stations are connected with the corre- 
spondingly numbered contacts. When, therefore, 
the trailing contact finger at each station simul- 
taneously touches the contacts bearing the same 
number, the corresponding instruments connected 




HWIM- -MiUK'lilil-' 



Fig. 546, Working and Receiving Currents. 

with these contacts at each station will be placed 
in communication over the main line, the trailing 
contact finger f, completing the connection of 
the main line with the contact arm in the man- 
ner already described. 

Telegraphy, Time A system for 

the telegraphic transmission of time. 

A system of time telegraphy includes a master 
clock, the movements of whose pendulum automati- 
cally transmit a number of electric impulses to a 
number of secondary clocks and thus moves them; 
or self-winding clocks are employed, which are 
corrected daily by an impulse sent over the line 
from a master clock. (See Clock, Electric.) 

Telegraphy, Writing' A species of 

fac-simile telegraphy, by means of which 
the motions of a pen attached to a transmit- 
ting instrument so vary the resistance on 
two lines connected with a receiving instru- 
ment as to cause the current received thereby 
to reproduce the motions, on a pen or stylus, 
which transfers them to a sheet of paper. 



A system of writing telegraphy consists 
essentially of transmitting and receiving in- 
struments connected by a double line wire. 

The transmitting instrument is shown in Fig, 
547- 




mnui.imV 

R 

Fig. 547. Transmitter of Writing Telegraphy. 

A stylus or pen resting on a top plate, is con- 
nected by the rod C, with a series of steel contact 
springs S, S, secured to the base and placed at 
right angles to one another. A series of resist- 
ances R, R, are connected with the lower ends 
of these contact springs. Two contact bars, 
B, B, are provided on the side facing the springs 
with platinum contacts opposite the contacts on 
the springs. The stylus rod C, is securely fixed 
to the base, but a spring at the lower end per- 
mits of its free movement. A pressure block at 
P, is fastened to the stylus rod, as shown, and in 
its normal position the pressures are adjusted so 
that contact is secured with the first spring. 

A movement of the stylus, as in writing, 
presses the contact bar against the spring, vary- 
ing the position and number of contacts, and 
thereby cutting in or out the resistance necessary 
to effect the proper movement of the receiving 
pen. 

The receiving instrument is shown in Fig. 548. 
It consists of two electro-magnets placed at right 
angles to each other. A double armature sup- 



Tel.] 



519 



[Tel. 



ports the receiving stylus or pen in the manner 
shown. The variations in the current sent over 
the line by the varying resistances introduced 
into the circuit, or cut out or in by the action of 
the transmitting stylus, causes variations in the 
position of the double armature, under the vary-, 
ing magnetic attraction of the receiving electro- 
magnet, and thus causes the receiving pen to 
correctly reproduce the motions of the trans- 
mitting pen. 




&£' 54^. Receiver of Writing Telegraph. 

This system has been operated over a line 
nearly 500 miles in length, when it successfully 
reproduced written characters. 

The author is indebted for the drawings and 
the general facts to the Electrical Engineer of 
New York. 

Tele-Hydro-Barometer, Electric 

An apparatus for electrically transmitting to, 
and recording at a distant station the height 
of water or other liquid. 
Tele-Manometer, Electric — A 

gauge for electrically indicating and record- 
ing pressure at a distance. 

The tele-manometer includes a pressure gauge 
furnished with electric contacts operated by the 
movements of the needle of the steam gauge, for 
instance, and indicating and recording apparatus. 
An alarm bell is provided to call attention to any 



rise of the pressure above or its fall below the 
given or predetermined limits for which the 
hands have been set. 

Telemeter. — An apparatus for electrically 
indicating and recording at a distance the 
pressure on a gauge, the reading of a ther- 
mometer, or the indications of similar in- 
struments. (See Tele-Hydro-Barometer, 
Electric. Tele-Manometer, Electric. Tele- 
Thermometer, Electric?) 

Telephone. —To communicate by means 
of a telephone. 

Telephone. — An apparatus for the electric 
transmission of articulate speech. 

The articulating telephone, though first 
brought into public use by Bell, was invented by 
Reis, in Germany, in 1861. In America, after 
very protracted litigation, Bell has been decided 
legally to be the first inventor, but scientific men 
very generally recognize the principles of the in- 
vention to be fully anticipated by the earlier in- 
struments of Reis. Bell, however, is justly en- 
titled to the credit of inventing the first really 
successful telephone. 

In Bell's magneto -electric telephone, the 
transmitting and receiving instruments are iden- 
tical. A coil C, of insulated wire connected with 
the line, is placed on a core of magnetized steel, 
mounted opposite the centre of a circular dia- 
phragm of thin sheet iron, rigidly supported at 
its edges. 

In transmitting, the message is spoken into the 
mouth-piece at one end, as at D, in Fig. 549, and 
the to-and-fro motions thus 
imparted to the metallic 
diaphragm attached to the 
mouth-piece P, produce in- 
duction currents in the coil 
C, on the magnet M. (See In- 
duction, Electro-Dynamic. ) 
These impulses, passing over 
the main line E L, Fig. 550, 
produce similar movements 
in the diaphragm P', of the 
receiving instrument, at D', 
and thus cause it to repro- 
duce the message, in articu- s ~ 549* 
late sounds, to one listening at the receiving in- 
strument. A ground circuit is shown in the 
figure, as usually employed in practice, except 
for long distance and in large cities. 




Tel.] 



520 



[Tel. 



A magneto-telephone constitutes in reality a 
magneto-electric machine, driven or propelled by 
the voice of the speaker, in which the currents 
so produced instead of being commuted are em- 
ployed uncommuted to reproduce the uttered 
speech. 

In actual practice the instrument above de- 
scribed is replaced by the eiedro-?nagnetic tele- 




Telephone Circuit. 

phone, in which the to-and-fro motions of the 
transmitting diaphragm are caused to vary the 
resistance of a button of carbon, or a variable con- 
tact transmitter similar to 
that employed by Reis in 
some of his instruments. 
The variable resistance 
is placed in the circuit of 
a battery, so that on 
speaking into the trans- 
mitter, electric impulses 
are sent over the line and 
are received by a tele- 
phone with a magnet core 
provided with a coil in the 
main-line circuit. 

The telephone is ar- 
ranged for actual com- 
mercial use in the United 
States in the manner^, jji. Telephone Ap- 
shown in Fig. 551. paratus. 

Telephone, Bi A term sometimes 

applied to a double telephone receiver so ar- 
ranged as to permit of easy application to 
both ears of the listener at the receiving in- 
strument. 

Telephone Cords.— (See Cords, Tele- 
phoned) 

Telephone, Electro-Capillary A 

telephone in which the movements of the 
transmitting diaphragm produce currents by 
means of variations in the electromotive 
forces of the contact surfaces of liquids in 
capillary tubes. (See Phenomena, Electro- 
Capillary^) 

In Breguet's telephone both the transmitting 
and the receiving instruments are similar in con- 




struction and operate by means of electro-capil- 
lary phenomena. A vertical capillary tube com- 
municates at its upper end with an air space 
below a diaphragm, and at its lower end with a 
mercury surface on which rests a layer of acidu- 
lated water. 

A line wire connects the mercury reservoirs of 
the transmitting and receiving instruments, the 
remainder of the circuit being formed by another 
wire connecting the mercury near the upper parts 
of the two vertical tubes. 

The alterations in the contact surfaces at the 
transmitting end produced by the movements of 
the diaphragm, cause electric impulses that pro- 
duce similar movements of the diaphragm at the 
receiving end. 

Telephone, Electro-Chemical A 

name sometimes given to the Edison electro- 
motographic telephone. (See Telephone, 
Electro-M olograph ic.) 

Telephone, Electro-Motographic 

A telephone in which the receiver consists of 
a diaphragm of mica or other elastic material 
operated on the principle of the electro- 
mot ograph. 

A straight lever, which forms part of the line 
circuit, is rigidly attached at one end to the centre 
of the receiving diaphragm, and rests near its 
other end on the surface of a chalk cylinder 
moistened with a solution of caustic potash or 
potassium iodide, maintained in rotation by suit- 
able mechanical means. 

Electric impulses being sent into the line by the 
voice of a speaker talking at a transmitter of ordi- 
nary construction reduce the friction between the 
lever and the cylinder, and produce slipping 
movements of the lever that reproduce articulate 
speech in the receiving diaphragm. 

Telephone, Reaction An electro- 
magnetic telephone in which the currents in- 
duced in a coil of wire attached to the dia- 
phragm are passed through the coils of the 
electro-magnet, and thus react on and 
strengthen it. 

Telephone Switch, Automatic (See 

Switch, Telephone, Automatic.) 

Telephonic— Pertaining to the telephone. 

Telephonic Alarm.— (See Alarm, Tele- 
phonic?) 



Tel.] 



521 



[Tel. 



Telephonic Cable. — (See Cable, Tele- 
phonic?) 

Telephonic Exchange.— (See Exchange, 
Telephonic, System of.) 

Telephonic Exchange, System of 

(See Exchange, Telephonic, System of.) 

Telephonic Joints. — (See Joint, Tele- 
graphic or Telephonic?) 

Telephonically.— In the manner of the 
telephone. (See Telephone?) 

Telephoning-. — Communicating by means 
of the telephone. 

Telephote. — An apparatus for the tele- 
graphic transmission of pictures by means of 
the action of light on selenium. (See Tele- 
photography?) 

The telephote is sometimes called the pherope. 

Telephotography. — A system for fac- 
simile transmission by means of dots and 
lines transmitted by means of a continuous 
current whose intensity is varied by a trans- 
mitting instrument containing a selenium re- 
sistance. (See Telegraphy, Fac-Simile. 
Resistance or Cell, Selenium?) 

The transmitter consists of a dark box mounted 
on an axis, so as to be capable of a sidewise 
motion. The picture to be transmitted is 
thrown continuously on the face of the box by 
any lantern projection apparatus, and a small 
opening containing a selenium resistance receives 




wise continuous current in the circuit of which the 
selenium resistance is placed. 

The picture is received at the other end on a 
sheet of chemically prepared paper moved syn- 
chronously with the transmitting box. 

Telescope, Reading A telescope 

employed in electric measurements for read- 
ing the deflections of the galvanometer. 

The image of numbers on an illumined scale is 
seen in the mirror through the telescope, shown 
in Fig. 552. 

Teleseme.— A self-registering hotel an- 
nunciator, by means of which a dial operated 
in a room indicates on the annunciator the 
article or service required. 

Tele-Thermometer, Electric — An 

electric recording thermometer for indicating 
and recording temperature at a distance. 

The tele thermometer consists essentially of a 
transmitter and a receiver. The transmitter 
consists of a delicate thermometer provided with 
suitable contacts. The receiver, which is in 
circuit with the transmitter, has, in some forms, 
a recording dial on which a continuous record, 
for a day or week, is made. In cases where it is 
desired that a given maximum temperature shall 
not be exceeded, an alarm bell, connected with 
contacts on the dial face, is rung. 

Telluric Magnetic Force. — (See Force, 
Magnetic, Telluric?) 

Telpher Line. — (See Line, Telpher?) 
Telpherage.— A system for the convey- 
ance of carriages suspended from electric 




Fig. SS 2 ' Reading Telescope. 

the alternations of light and shade, and transmits 
the same as variations in the strength of the other- 



Fig. 553. Circuit for Telpherage System 

conductors, and driven by means of electric 
motors, that take directly from the conductors 
the current required to energize them. 



Tem.] 



522 



[The. 



Two lines are provided, an up and a down line, 
that cross each other at regular intervals. Each 
line is in segments, and the alternate segments 
are insulated from each other, but are connected 
electrically by cross-pieces on the supporting 
posts. In this way the line shown in Fig. 553 is 
obtained. 

The two lines are maintained at a difference of 
potential by a dynamo-electric machine at D, 
Fig. 554. As the train at L T, or L' T', is of 
such a length as to come into contact with two 
different segments at the same time, it receives a 
current sufficient to run the motor connected with 
it, the current being received through a conduc- 
tor joining a pair of wheels that are insulated 
from the truck. 

The general arrangement of the line is shown 
in the annexed Fig. 554 




Fig. SS4' Circuit for Telpherage System. 

Temperature Alarm. — (See Alarm, Tem- 
perature^) 

Temperature, Effects of, on Electric Re- 
sistance (See Resistance, Effect of 

Heat on Electric?) 

Tempering", Electric — A process 

for temperaing metals in which heat of elec- 
tric origin is employed instead of ordinary 
furnace heat. 

Temporary Intensity of Magnetization. — 

(See Magnetization, Temporary Intensity 
of.) 

Tension, Electric A term often 

loosely applied to signify indifferently surface 
density, electromotive force, dielectric stress, 
or difference of potential. 

This term is now very generally abandoned. 

Terminal, CaMe — A water-tight 

covering provided at the end of a cable to 
prevent injury to the cable insulation by the 
moisture of the air. 



Terminal, Negative 



-The negative 



pole of a battery or other electric source, or 
the end of the conductor or wire connected 
with the positive plate. 



Terminal, Positive The positive 

pole of a battery or other electric source, or 
the end of the conductor or wire connected 
to the negative plate. 

Terminals. — A name sometimes applied 
to the poles of a battery or other electric 
source, or to the ends of the conductors or 
wires connected thereto. 

The two terminals are distinguished as the 
positive and the negative. Their names are un- 
like those of the battery plates to which they 
are connected, the positive terminal being con- 
nected with the negative plate and the negative 
terminal with the positive plate. 

Terrestrial Magnetism. — (See Magnet- 
ism, Terrestrial?) 

Testing, Methods of —Various 

methods for determining the values of the 
current strength in any circuit, the difference 
of potential, the resistance, the coulombs, 
the farads, the joules, the watts, etc. (See 
Measure?nents, Electric?) 

The investigation of an apparatus or cir- 
cuit for the purpose of determining whether 
it is in standard or working condition. 

Testing of Joints. — (See Joint, Test- 
ing of.) 

Testing Pole.— (See Pole, Testing?) 

Testing Transformer. — (See Trans- 
former, Testing?) 

Tetanus. — Continuous, spasmodic contrac- 
tion of the muscles. 

Tetanus, Acoustic Tetanus pro- 
duced in a muscle by means of alternate 
currents induced in a coil of wire by a mag- 
netized steel spring vibrating near the coil 
with sufficient rapidity to give a musical note. 

The rapidity of the inductive shock can be de- 
termined from the pitch of the musical note; hence 
the use of the term acoustic. 

Theatrophone. — A system of telephonic 
communication between theatres or operas 
and subscribers, by means of slot machines. 

Any person at a cafe, club, restaurant or other 
public place, by the theatrophone, is automati- 
cally placed in communication with the theatre 
by means of a receiving telephone so as to hear 



The.] 



523 



[The. 



the performance by dropping a given piece of 
money in the slot of the machine. 

Theodolite, Magnetic — An appa- 
ratus for measuring the declination or varia- 
tion of the magnetic needle at any place. 

A divided circle, like that on a theodolite, is 
supported horizontally. The needle is formed of 
a tubular magnet, having an achromatic lens at 
one end and a scale at the focus of the lens at the 
other end. 

Theory, Alternation, of Muscular Nerve 

Current — A theory proposed by L. 

Hermann, in which the currents of nerves or 
muscular fibres are regarded as a result of 
their alteration from an original condition. 

Hermann states: 

(i.) That protoplasm undergoing partial death 
at any part, either while dying or by metamor- 
phosis, becomes negative to the uninjured part. 

(2.) Protoplasm, when excited at any part, be- 
comes negative to the unexcited part. 

(3.) Protoplasm, when partially heated at any 
part, becomes positive, and, on cooling, negative 
to the unchanged part. 

(4. ) Protoplasm is strongly polarizable on its 
surface, the polarization constantly diminishing 
with excitement and while dying. 

According to this theory, passive, uninjured 
and absolutely fresh tissues are devoid of elec- 
tric currents. This matter must still be regarded 
as unsettled. (See Theory, Molecular, of Mus- 
cles or Nerve Current. ) 

Theory, Contact, of Toltaic Cell 

(See Cell, Voltaic, Contact Theory of.) 

Theory, Difference A theory as to 

the cause of the electric currents excited be- 
tween injured and uninjured protoplasm. 

Theory, Molecular, of Muscles or Nerve 

Current A theory proposed by Du 

Bois Reymond, in which every nerve or mus- 
cular fibre is regarded as composed of a 
series of electromotive molecules arranged 
in series and surrounded by a neutral con- 
ducting fluid. 

" The molecules are supposed to have a posi- 
tive equatorial zone directed towards the surface 
and two negative polar surfaces directed toward 
the transverse section. Every fresh transverse 
section exposes new negative surfaces, and every 



artificial longitudinal section new positive area." 
— [Landois and Sterling.) 

Theory of Electric Displacement. — (See 
Displacement, Electric, Theory of.) 

Therapeutical Electrization. — (See Elec- 
trization, Therapeutical?) 

Therapeutic Bath, Electro —(See 

Bath, Electro- Therapeutic) 

Therapeutics, Electro, or Electro- 
Therapy The application of electricity 

to the curing of disease. (See Biology, Elec- 
tro) 

Therapeutist, Electric One skilled 

in electro-therapy. 

An electro-medical practitioner. 

Therapy, Electro — A term some- 
times used instead of electro-therapeutics. 
(See Therapeutics, Electro, or Electro- 
Therapy) 

Therapy, Magneto Alleged electro- 
therapeutic effects produced by the move- 
ments of magnets over the body of the 
patient. 

It is asserted by eminent authorities that such 
effects have an actual existence. They should, 
however, until more carefully investigated, be 
accepted with extreme caution. 

Therm.— A heat unit proposed by the 
British Association. 

A therm is the amount of heat required to 
raise the temperature of one gramme of pure 
water at the temperature of its maximum density 
one degree centigrade. (See Calorie.) 

Thermaesthesiometer.— An instrument 
employed in electro-therapeutics for testing 
the temperature sense in nervous diseases. 

The thermaesthesiometer consists of two ther- 
mometers movable on a standard, with flat ves- 
sels of mercury in order to readily apply them to 
the skin. The mercury vessel of one of the two 
thermometers is surrounded by an insulated 
platinum wire and may be warmed at pleasure by 
passing a galvanic current through the wire. 

The two vessels, brought to different tempera- 
tures, are set on the same part of the skin, one 
after the other, so as to test the sensibility of the 
skin for the differences in temperature. 

Thermal Absorption. — (See Absorption, 
Thermal.) 



The.] 



524 



[The. 



Thermal Cautery. — (See Cautery, Ther- 
mal) 

Thermal Incandescence. — (See Incan- 
descence, Thermal) 

Thermic Balance. — (See Balance, Ther- 
mic, or Bolometer) 

Therino-Battery.— (See Battery, Thermo) 

Thermo Call. — A call operated by means 
of thermo currents. 

Thermo-Cell.— (See Cell, Thermo-Elec- 
tric) 

Thermo-Electric Battery. — (See Battery y 
Th erm o-Electric) 

Thermo-Electric Cell.— (See Cell, 
Thermo-Electric) 

Thermo-Electric Couple. — (See Couple, 
Th erm o-Electric) 

Thermo-Electric Diagram. — (See Dia- 
gram, Thermo-Electric ) 

Thermo-Electric Effect.— (See Effect, 
Th ermo-Electric) 

Thermo-Electric Inversion. — (See In- 
version, Thermo-Electric) 

Thermo-Electric Pile, Differential — - 
— (See Pile, Thermo, Differential) 

Thermo-Electric Pile or Battery. (See 

Pile, Thermo-Electric) 

Thermo-Electric Power. — (See Power, 
Thermo-Electric) 

Thermo-Electric Series. — (See Series, 
Thermo-Electric) 

Thermo-Electricity.— (See Electricity, 
Thermo) 

Thermo-Electrometer. — A name some- 
times, but not happily, applied to an electric 
thermometer. (See Thermometer, Electric) 

Thermo-Electromotive Force. — (See 
Force, Electromotive, Thermo) 

Thermolysis. — A term applied to the 
chemical decomposition of a substance by 
heat. 

Thermolysis, or dissociation, is an effect pro- 
duced by an action of heat somewhat similar to 
the effect of electrolysis, or chemical decomposi- 
tion produced by the passage of an electric cur- 
rent. When a chemical substance is heated, the 



vibration of its molecules is attended by an inter- 
atomic vibration of its constituent atoms so that a 
decomposition ensues. If the temperature is not 
excessive, these liberated atoms recombine with 
others which they meet. At higher temperatures, 
however, such recombination is impossible, and a 
permanent decomposition ensues, called ther- 
molysis or dissociation. 

Thermometer, Electric A device 

for determining the effects of an electric dis- 
charge by the movements of a liquid column 
on the expansion of a confined mass of air 
through which the discharge is passed. 

Thermometer, Electric Resistance 

— A thermometer the action of which is 
based on the change in the electric resistance 
of metallic substances with changes in tem- 
perature. 

The electric resistance thermometer is used, 
among other purposes, for determining the temper ~ 
ature of the sea at different depths. Its operation 
is based on the electric resistance of two perfectly 
similar coils of insulated wire, enclosed in separate 
water- tight copper cases. One coil is placed where 
the temperature is to be determined, and the other 
in a vessel of water, the temperature of which is 
altered until the two coils show the same resist- 
ance, when, of course, the temperature of the 
distant coil is the same as that of the water sur- 
rounding the other coil. 

Thermometer Scale, Centigrade 

(See Scale, Thermometer, Centigrade) 

Thermometer Scale, Fahrenheit 

(See Scale, Ther?nometer, Fahre?iheit) 

Thermophone. — Any instrument by means 
of which sounds are produced by the absorp- 
tion of radiant energy. (See Photophone) 

A telephone has been constructed in which the 
motions of the receiving diaphragm are effected 
by the expansions and contractions of a thin me- 
tallic wire connected to the diaphragm and placed 
in the circuit of the main line. 

Thermostat. — An instrument for automati- 
cally maintaining a given temperature by the 
closing of an electric circuit through the ex- 
pansion of a solid or liquid. 

Thermostats are often used in systems of auto- 
matic fire telegraphy and in systems of automatic 
temperature regulation in connection with indi- 



The.] 



525 



[Tic. 



-A thermo- 



cating instruments for sounding an alarm or giv- 
ing notice when the temperature changes. 

They are operated either on open or closed cir- 
cuits. 

Thermostat Alarm. — (See Alarm, Ther- 
mostat) 

Thermostat, Closed-Circuit — A 

thermostat maintained normally on a closed 
circuit. 

In closed-circuit thermostats, the adjustment 
for any degree of temperature within a given 
range is effected by means of a screw. 

Thermostat, Electro-Pneumatic 

An instrument for automatically indicating 
the existence of a given temperature by the 
closing of an electric circuit on the expansion 
of a gas. 

Thermostat, Mercurial 
stat operating by the ex- 
pansion of a mercury 
column. 

A mercurial thermostat 
is shown in Fig. 555. One 
terminal is connected di- 
rectly with the mercury; 
the other is placed in the 
arm to the left. On a cer- 
tain predetermined tem- 
perature being reached, the 
rise of the mercury column 
completes the circuit and 
rings an alarm bell. By 
connecting the thermostat 
with an annunciator, the 
particular locality where an 
excessive temperature has 
been reached is indicated. 
Such a system is in use in a well known system of 
fire alarm. 

Thermostat, Open-Circuit A ther- 
mostat maintained normally on an open cir- 
cuit. 

In open-circuit thermostats the adjustment for 
temperature within a given range is effected by 
varying the distance of the fixed and movable 
contact points. 

Thermostatic. — Of or pertaining to a ther- 
mostat. (See Thermostat.) 

Thompson's Gauss. — (See Gauss, S. P. 
Thompson's.) 




Fig. SSS- Mercurial 
TTiermostat. 



Thomson's Gauss. — (See Gauss, Sir Wil- 
liam Tho?nsons) 

Three-Branched Sparks. — (See Spark, 
Three-Branched.) 

Three-Filament Incandescent Electric 
Lamp for Multiphase Circuits. — (See Lamp, 
Electric, Inca?idescent, Three-Filament, 
for Multiphase Circuits) 

Three-Way Trolley Frog. — (See Frog, 
Trolley, Three-Way) 

Three- Wire System.— (See System, Three- 
Wire) 

Throttling*. — Choking, or stopping off. 

Through Circuit. — (See Circuit, 
Through) 

Through Line. — (See Line, Through) 

Throwback Indicator, Electrical 

(See Indicator, Electric Throwback) 

Throwback Indicator, Mechanical 

— (See Indicator, Mechanical Throwback.) 

Throw of Xeedle. — (See Needle, Throw 
of.) 

Thumb-Cock Electric Burner. — (See 
Burner, Thumb-Cock Electric) 

Thunder. — A loud noise accompanying a 
lightning discharge. 

Thunder is due to the sudden rush of the sur- 
rounding air to fill the partially vacuous space 
accompanying the disruptive discharge of a cloud. 
This space is caused mainly by the condensation of 
the vapor formed on the passage of the discharge 
through drops of rain or moisture in the air, as 
well as by the expansion of the air itself. 

Thunder Rod.— (See Rod, Thunder) 

Thunder Storms, Geographical Distribu. 
tion of (See Storms, Thunder, Geo- 
graphical Distribution of) 

Tick, Magnetic A faint metallic 

click heard on the magnetization and demag- 
netization of a magnetizable substance. 

Ticker Sendee, Stock The simul- 
taneous transmission of stock quotations or 
other desired information to a number of 
subscribers. 

The stock ticker-service includes a central 
transmitting station connected with a given num- 



Tic] 



526 



[Tis. 



ber of subscribers, each of whom is furnished 
with a stock ticker. The transmitter at the cen- 
tral station consists of a keyboard and a cylinder 
furnished with spiral pins. The spiral pins are 
connected through a series of pole-changers to 
separate line wires radiating in all directions from 
the central office. 

The connections are such that, a rapid rota- 
tion being given by means of an electric mo- 
tor to the cylinder, the impulses sent out by the 
keyboard are transmitted to each of the separate 
circuits. Since each of these circuits has a num- 
ber of ticker printers connected with it, reports of 
fluctuations in prices are simultaneously printed 
in hundreds of different offices. 



Time-Constant of Electro-Magnet— (See 

Constant \ Time, of Electro-Magnet) 



Ticker, Stock 



■A form of step-by- 



step telegraphic instrument employed for au- 
tomatically sending and recording stock quo- 
tations to any desired number of subscribers. 
(See Telegraphy, Step-by- Step >.) 
A form of printing telegraph. 

Callahan's Printing Telegraph is used as a 
stock ticker. (See Telegraphy ', Printing.) 

Phelps' Stock Printer is employed extensively 
as a stock ticker. This form of printing telegraph 
requires but a single wire, and has a working 
speed of almost thirty words a minute. 

A double type-wheel, maintained in motion by 
clockwork, is stopped at the desired characters 
by the motion of a polarized relay, working be- 
tween the poles of two electro-magnets, furnished 
with a soft iron or non-polarized armature. The 
release of the armature of the printing mag- 
net releases a train, and thus insures the impres- 
sion of the character it is desired to print. 

The type-wheel is driven by a step-by-step 
movement obtained by means of rapidly alter- 
nating pulsations. Although these pass through 
the coils of the printing magnet, they follow one 
another too rapidly to charge its coils, so that the 
armature is unaffected until a pause is made, 
when, its armature being attracted, it releases 
the printing mechanism. The message is received 
on a fillet of paper, fed by a suitable mechanism. 

Time-Ball, Electric (See Ball, 

Electric Tinted) 

Time-Constant of Circuit. — (See Circuit, 
Time-Constant of.) 

Time-Constant of Condenser. — (See Con- 
denser, Time-Constant of.) 



Time Cut-Out, Automatic 



-An au- 



omatic cut-out arranged on a storage bat- 
tery so as to cut it in or out of the circuit of 
the charging source at predetermined times. 

Time-Fall of Electromotive Force of 
Secondary or Storage Cell During Dis- 
charge. — (See Force, Electromotive, of Sec- 
ondary or Storage Cell, Time-Fall of) 

Tinie-Lag of Magnetization.— (See Mag- 
netization, Time-Lag of.) 

Time, Reaction The time required 

for the effects of an electric current to pass 
from a nerve to a muscle. 

Time-Rise of Electromotive Force of 
Secondary or Storage Cells During Dis- 
charge. — (See Force, Electromotive, of Sec- 
ondary or Storage Cell, Time-Rise of.) 

Time-Switch. — (See Switch, Time.) 

Time, Telegraphic, Register for Rail- 
roads (See Register, Time, for Rail- 
roads) 

Time Telegraphy. — (See Telegraphy, 
Time.) 

Tinned Wire.— (See Wire, Tinned) 

Tinning, Electro Covering a sur- 
face with a coating of tin by electro-plating. 
(See Plating, Electro) 

Stannic chloride, or the perchloride of tin, dis- 
solved in water in the proportion of 30 parts of the 
salt to 1,250 of water, makes a good tinning 
bath. 



Tinnitus, Telephone 



-A professional 



neurosis, or abnormal nervous condition of the 
auditory apparatus, believed to be caused by 
the continual use of the telephone. 

Tips, Polar The free ends of the 

field magnet pole pieces of a dynamo-electric 
machine. 

Tissue, Nerve or Muscular Excitability 

of Electric stimulation of nervous or 

muscular tissue. 



Ton.] 



527 



[Tor. 



The general effects of electric stimulation of 
nervous or muscular tissue may be summarized 
as follows: 

(i.) Electric stimulation of a motor nerve, pro- 
duces a contraction of the muscles to which such 
nerve is distributed. 

(2.) Electric stimulation of a sensory nerve, 
produces pain in the parts to which the nerve is 
distributed. 

(3.) Electric stimulation of mixed motor and 
sensory nerves produces both of the effects men- 
tioned under (1) and (2.) 

Tongs, Cable Hanger Tongs pro- 
vided with long handles for the purpose of 
attaching the hangers of an aerial cable to 
the suspending wire or rope. 

Tongs, Discharging A term some- 
times used for a discharging rod. (See Rod, 
Discharging) 

Tongue, Relay, Bias of A term 

employed to signify such an adjustment of a 
polarized relay, that on the cessation of the 
working current, the relay tongue shall 
always rest against the insulated contact, and 
not against the other contact, or vice versa. 

Sometimes, as in the split-battery duplex, the 
bias is toward the uninsulated contact. (See 
Relay, Polarized.) 

Tool, Lead Scoring A tool for 

readily scoring the surface of the lead of a 
lead-covered cable, when the same is to be 
removed preparatory to making joints. 

Toothed-Ring Armature. — (See Arma- 
ture, Toothed-Ring.) 

Top, Induction A top consisting 

of an iron disc supported on a vertical axis, 
which, when spun before the poles of a steel 
magnet, assumes an inclined position, through 
the influence of the currents induced in the 
disc. 

The top maintains the inclined position so long 
only as the strength of the induced currents is 
sufficiently great ; that is, while speed of rotation 
is sufficiently great. 

Toppler-Holtz Machine. — (See Machine, 
Toppler-Holtz) 
Torch, Electric Gaslighting A 

gaslighting appliance consisting of the com- 



bination of a portable voltaic battery and a 
spark or induction coil. 

The torch is mounted on the end of a rod pro- 
vided with means for turning on the gas. A key 
is then touched and the gas lighted by the spark 
produced by an induction coil or a small electro- 
static induction machine. 

Torpedo, Automobile A torpedo 

which contains in itself the power for its own 
motion. 

The moving power may be that derived from 
compressed air or gas, or from a storage bat- 
tery contained within the torpedo. An auto 
mobile torpedo provided with a storage battery 
and electric motor would then be distinguished 
from an electrically propelled torpedo, connected 
by means of cables with a driving dynamo 
located outside the torpedo on a ship, or on the 
shore. 

Torpedo Boat. — (See Boat, Torpedo) 

Torpedo Cable.— (See Cable, Torpedo) 

Torpedo, Drifting A torpedo sus- 
pended from a float, and connected by means 
of rope with similar torpedoes, allowed to 
drift with the current, so as to catch against 
a vessel. 

Torpedo, Electric A name some- 
times given to the electric ray. (See Ray, 
Electric.) 

Torpedo, Electric An electrically 

operated torpedo. 

This latter usage of the term is the commoner. 

Torpedo, Halpine-Savage A special 

form of torpedo, in which electricity is both 
the propelling and directing power, and in 
which the electric source furnishing the pro- 
pelling current is contained within the 
torpedo. 

In the Halpine-Savage torpedo, the propelling 
power is obtained from a storage battery placed 
within the torpedo. 

Torpedo, Lay A moving torpedo, 

in which the moving power is carbonic acid 
gas, or compressed air, or other similar power 
not electric, and the guiding power is electric. 

The Lay torpedo has the form of a cylindrical 
boat furnished with conical ends. The explosive is 
placed in the fore part of the torpedo. Flags are 



Tor.] 



528 



[Ton. 



attached to the torpedo, showing the operator the 
exact course taken by it. 

The torpedo is started, stopped and steered by 
means of electric currents sent to the torpedo 
through an insulated cable connected with the 
torpedo. 

Torpedo Nets.— (See Nets, Torpedo?) 

Torpedo, Outrigger A pole or 

spar torpedo. 

The torpedo is placed in a metallic case and 
supported on the end of a spar or outrigger. The 
spar is depressed until the torpedo is sunk below 
the water line. The torpedo is fired when its end 
comes in contact with the side of the enemy's 
vessel. 

Torpedo, Sims-Edison A special 

form of torpedo in which electricity is both 
the propelling and the directing power, but the 
electric source is situated outside of the 
torpedo. 

The torpedo is propelled by means of an electric 
motor placed in the torpedo, and driven by means 
of an electric current transmitted through a cable 
connected with the sending station. 

Torpedo, Spar A torpedo, attached 

to the end of a spar, and designed to be 
exploded by percussion against the side of an 
enemy's vessel, when thrust against the side 
below the water-line. 

The spar torpedo is but little used, having 
been replaced by more efficient forms. 

— A term some- 



Torpedo, Stationary 



times employed instead of a submarine 
mine. (See Mine, Submari?ie?) 

A stationary torpedo is so named in order to 
distinguish it from a torpedo which is moved 
through the water by any means. (See Torpedo, 
Towing. ) 

Torpedo, Towing A torpedo ar- 
ranged to be towed on the surface after a ves- 
sel and explode when it strikes the side of 
an enemy's vessel. 

The torpedo is shaped so that it maintains dur- 
ing its motion a certain distance from the sides of 
the towing boat or vessel. 

Torque. — That moment of the force ap- 
plied to a dynamo or other machine which 
turns it or causes its rotation. 



The mechanical rotary or turning force 
which acts on the armature of a dynamo- 
electric machine or motor and causes it to 
rotate. 

In the case of the armature of a dynamo- 
electric machine the torque is equal to the radius 
of the armature, multiplied by the pull at the 
circumference, or the radius of its pulley multiplied 
by the pull at the circumference of the pulley. 

A torque is exerted on the shaft of a motor from 
the electro-magnetic action, or pull at the 
periphery of the armature. 

The torque is usually measured in pounds of 
pull at the end of a radius or arm I foot in 
length. 

Torricellian Vacuum. — (See Vacuum, 
Torricellian?) 

Torsion Balance, Coulomb's (See 

Balance, Coulomb's Torsion?) 

Torsion Galvanometer.— (See Galvanom- 
eter, Torsion?) 

Total Disconnection. — (See Disconnec- 
tion, Total?) 

Total Earth.— (See Earth, Total.) 

Total Magnetic Induction. — (See Induc- 
tion, Total Magnetic.) 

Touch, Double A method of mag- 
netization in which two closely approximated 
magnet poles are simultaneously drawn from 
one end of the bar to be magnetized to the 
other and back again, and this repeated a 
number of times. 

Touch, Separate A method of 

magnetization in which two magnetizing poles 
are simultaneously applied to the bar to be 
magnetized and drawn over it in opposite di- 
rections. [See Magnetization by Touch?) 

Touch, Siugle A method of mag- 
netization in which a single magnetizing bar 
is drawn from one end to the other of the bar 
to be magnetized, and returned through the 
air for the next stroke. (See Magnetization, 
Methods of.) 

Tourmaline. — A mineral consisting of 
natural silicates and borates of alumina, lime, 
iron, etc., possessing pyro-electric properties. 
(See Electricity, Tyro.) 



Tow.] 



529 



[Tra. 



Tower, Conning 



-A shot-proof 



tower from which the commander of a turret 
ship directs the movements of a vessel during 
action. 

Tower, Electric A high tower pro- 
vided for the support of a number of electric 
arc lamps, employed in systems of general 
illumination. 

Tower System of Electric Lighting. — 
The lighting of extended areas by means of 
arc lights placed on the tops of tall towers. 

The tower system of electric illumination is only 
applicable to wide open spaces, since otherwise 
objectionable shadows are apt to be formed. 

Towing Torpedo. — (See Torpedo, Tow- 
ing.) 

Traction, Magnetic The force with 

which a magnet holds on to or retains its 
armature, when once attached thereto. 

Magnetic traction is to be distinguished from 
magnetic attraction, or the ability of a magnet 
pole to draw an armature or other magnets to- 
wards it from a distance. 

Train Wire. — (See Wire, Train.) 

Tramway, Electric A railway over 

which cars are driven by means of elec- 
tricity. 

An electric railroad. 

The term tramway is sometimes applied to 
roads in cities, as distinguished from inter-urban 
roads. 

Transformer. — An inverted Ruhmkorff 
induction coil employed in systems of dis- 
tribution by means of alternating currents. 

A transformer is sometimes called a converter. 
The word transformer is, however, the one most 
employed. 

A transformer consists essentially of an induc- 
tion coil, Fig. 556, in which the primary wire is 
long and thin, and consequently has many turns, 
as compared with the secondary wire, S, S, which 
is short, thick, and has few turns. 

To prevent heating and loss of energy in con- 
version, the core of the transformer is thoroughly 
laminated; to lower the resistance of its mag- 
netic circuit, the transformer is usually iron-clad. 

In a system of electrical distribution by means 
of transformers, alternating currents, of small 
current strength and comparatively considerable 



difference of potential, are sent over a line from a 
distant station, and passing into the primary wire 
of a number of converters, generally connected 
to the line in multiple arc, produce, by induction, 




Fig. 556. Transformer. 

currents of comparatively great strength and 
small difference of potential in the secondary 
wires. 

Various electro -receptive devices are connected 
in multiple arc to circuits connected with the sec- 
ondary wires. 

This method of distribution greatly reduces the 
cost of the main conducting wires or leads in all 
cases where the distance is considerable, since 
considerable energy may be conveniently sent 
over a comparatively thin wire, with but a trifling 
loss, if the difference of potential is sufficiently 
great. 

The general arrangement of the converters on 
the main line, and the connection of the second- 
ary circuits with the electro-receptive devices in 




Fig. JS7- Transformer Circuits. 

such a system, are shown in Fig. 557. The trans- 
formers are supported on the line poles, as more 



Tra.] 



530 



[Tra. 



clearly shown in Fig. 558, in which the terminals 
of the primary and secondary of the converter 
are readily seen. 

When the converter is properly constructed, 
the loss of conversion at full load is but small; 
that is to say, the number of watts in the secon- 
dary is very nearly equal to the number in the 
primary. A current of 10 amperes, at 2,000 
volts, when passed into a converter the number 
of whose turns in the primary is twenty times the 
number in its secondary, will produce in its sec- 
ondary a current whose strength is about twenty 
times as great, that is, nearly 200 amperes, but 
whose voltage is only about one-twentieth, or, 
100; the watts in the two cases are nearly the 
same, or theoretically 20,000 watts. 

The ratio between the windings of the primary 
and the secondary circuits is called the co-effi- 
cient of transformation. 

In general, the shorter the wire on the second- 
ary, and the smaller its number of turns, the 
greater is the reduction in the difference of po- 
tential, and the greater the current produced. 
The reduction is nearly proportionate to the ratio 
of the number of windings of the two coils. 



Transformer, Constant-Current 




Fig. 558. Transformer Attached to Poles. 

Transformer, Closed Iron Circuit 

— A transformer the core of which forms a 
complete magnetic circuit. 

These transformers are sometimes called iron- 
clad transformers. 

Transformer, Commuting A term 

sometimes applied to a variety of motor gen- 
erator in which neither the armature nor the 
field magnets revolve, the variations in the 
polarity of the magnetic circuit being obtained 
by means of special commutators. 



transformer in which a current of a constant 
potential in the primary is converted into a 
current of constant strength in the secondary, 
despite changes in the load on the secondary. 

Transformer, Core A transformer 

in which the primary and secondary wires 
are wrapped around the outside of a core 
consisting of a bundle of soft iron wires or 
plates. 

A Ruhmkorff coil is a core transformer. 

Transformer, Efficiency of — The 

ratio between the whole energy supplied in 
any given time to the primary circuit of a 
transformer and that which appears in the 
form of electric current in the secondary 
circuit. 

The energy applied to the primary circuit of a 
transformer is dissipated: 

(1.) By eddy currents in the core of the trans- 
former. (See Currents, Eddy.) 

(2.) By hysteresis, or magnetic friction. (See 
Hysteresis. ) 

(3.) By heating of the primary circuit. 

(4.) By heating of the secondary circuit. 

When a transformer is overloaded, its efficiency 
decreases. There is a certain range of second- 
ary resistance and current, within which a trans- 
former is most advantageously operated. 

Transformer Guard. — (See Guard, Trans- 
former, Lightfii?tg^) 

Transformer, Hedgehog A name 

applied to a particular form of open-iron cir- 
cuit transformer. (See Transformer.) 

The advantages claimed for the hedgehog trans- 
former are that it can be made to give a higher 
all- day efficiency, since it insures a smaller loss 
from hysteresis in the iron. The efficiency for 
very small loads, or for no loads is greater than in 
the closed-circuit transformer. 

Transformer, Leakage Current of 

A term sometimes used for the current which 
escapes from the primary through the dielec- 
tric of a transformer to the secondary circuit. 

The term is a bad one, since the true leakage 
current would be the current which represents 
the leakage between the primary or secondary 
circuit and the ground. 



Tra.] 



531 



[Tra. 



Transformer Lightning" Arrester.— (See 
Arrester, Lightning, Transformer?) 

Transformer, Multiple Any form 

of transformer which is connected in multiple 
to the primary circuit. 

A multiple or parallel transformer is self-regu- 
lating under variable loads, provided the electro- 
motive force in the primary is maintained con- 
stant. 

Transformer, Oil A transformer 

which is immersed in oil in order to insure a 
high insulation. 

Transformer, Open-Iron Circuit 

A transformer the iron of which does not form 
a complete magnetic circuit, but is formed 
instead partly of iron and partly of air. 

Transformer, Pilot A small trans- 
former, placed at any desired portions of a 
line in order to determine the drop of poten- 
tial. 

The pilot transformer is used in connection with 
a lamp or other suitable indicating device. Its use 
is similar to the use of the pilot incandescent lamp. 

Transformer, Rotary-Current A 

transformer operated by means of a rotary 
current. (See Current, Rotating?) 

The rotary current transformer for a rotary 
current of three separate alternating currents com- 
bined, transforms all three currents together. 
There are three cores, connected at one set of 
ends and at the other to the circumference of an 
iron ring. Each core contains a primary and 
secondary wire. 

Transformer, Rotary-Phase A ro- 
tary current transformer. (See Transfor- 
mer, Rotary-Current?) 

Transformer, Series Transformers 

which are connected in series with the pri- 
mary circuit. 

A series transformer is not as readily made self- 
regulating under variations in the load as a mul- 
tiple transformer. If, however, its core is not 
saturated, and the electromotive force of its 
secondary is small, it can be made fairly self- regu- 
lating. Series transformers are used in the 
Jablochkoff system for feeding arc lamps in the 
shape of Jablochkoff candles. 

Transformer, Shell A transformer 



in which the primary and secondary coils are 
laid on each other, and the iron core is then 
wound through and over them so as to en- 
close all the copper of the primary and 
secondary circuits within the iron. 

The iron shell surrounding the copper may 
consist of the thin plates of iron, built up so as to 
leave a rectangular space for the introduction of 
the primary and secondary. 

Transformer, Step-Down A trans- 
former in which a small current of compara- 
tively great difference of potential is con- 
verted into a large current of comparatively 
small difference of potential. 

An inverted Ruhmkorff induction coil. 

Transformer, Step-Up — A trans- 
former in which a large current of compara- 
tively small difference of potential is con- 
verted into a small current of comparatively 
great difference of potential. 

The term step-up transformer is used in contra- 
distinction to the step -down transformer. 

The old form of Ruhmkorff coil is an example 
of a step-up transformer. 

Transformer, Testing — A trans- 
former employed in any system of distribu- 
tion for the purposes of testing for grounds, 
condition of line, drop of potential, etc. 

Transformer, Welding A trans- 
former suitable for changing a small electric 
current of comparatively high difference of 
potential, into the heavy currents of low 
difference of potential required for welding 
purposes. 

Welding transformers have in general a very 
low resistance in their secondary coils, and almost 
invariably consist of a single turn or at the most 
of a few turns of very stout wire. 

Transforming Currents. — (See Current, 
Transforming a.) 

Transforming Down. — Transforming by 
means of a step-down transformer. (See 
Transformer, Step-Down.) 

Transforming Station. — (See Station, 
Transform ing.) 

Transforming Up. — Transforming by 
means of a step-up transformer. (See 
Tra?isformer, Step- Up) 



Tra.] 



532 



[Tra. 



Transient Currents. — (See Currents, Transmission, Multiple 

Transient?) 

Transit, Magnetic Tariation An 

apparatus for measuring the declination or 
variation of the magnetic needle at any place. 
The variation transit generally consists of an 
altitude and azimuth instrument, the telescope of 
which is so arranged as to be readily converted 
into a microscope. 

Transition Kesistance. — (See Resistance, 
Transition?) 

Translater, Double-Current — A 

telegraphic translater or repeater designed to 
operate on double current transmission. 

Translater, Single-Current A tele- 



— The simul- 
taneous sending of more than two messages 
over a single line or conductor. 

Transmission of Energy. — (See Energy, 
Electric, Transmission of.) 

Transmitter, Carbon, for Telephones 

A telephone transmitter consisting of 

a button of compressible carbon. 

The sound waves impart to-and-fro movements 
to the transmitting diaphragm, and this to the 
carbon button, thus varying its resistance by pres- 
sure. This button is placed in circuit with the 
battery and induction coil. (See Telephone.) 



Transmitter, Double-Current 



-The 



graphic translater or repeater designed to 
operate a single-current transmission. 

Translater, Telegraphic — A term 

sometimes applied to a telegraphic repeater. 
(See Repeaters, Telegraphic?) 

Translating Device. — (See Device, Trans- 
lating.) 

Translating Devices, Multiple-Arc-Con- 
nected (See Devices, Translating, 

Multiple-Arc-Connected.) 

Translating Devices, Multiple-Con- 
nected — (See Devices, Translating, 

Multiple- Connected?) 

Translating Devices, Multiple-Series- 
Connected (See Devices, Translat- 
ing, Multiple- Series- Connected?) 

Translating Devices, Series-Connected 

■ (See Devices, Translating, Series- 

Connected.) 

Translating Devices, Series-Multiple- 
Connected (See Devices, Translat- 
ing, Series-Multiple- Connected.) 

Translucent-Disc Photometer. — (See 
Photometer, Translucent-Disc.) 

Transmission, Double The simul- 
taneous sending of two messages over a sin- 
gle wire in opposite directions. (See Teleg- 
raphy, Duplex, Bridge Method of.) 



transmitting instrument employed in systems 
of telegraphy, by means of which the direc- 
tion of the currents on the line is alternately 
changed, according to whether the key rests 
on its front or on its back stop. 

Double-current transmitters are used in con- 
nection with instruments, such as polarized re- 
lays, which respond to change in the direction of 
the current, rather than to changes in its in- 
tensity. 

Transmitter, Electric A name 

applied to various electric apparatus employed 
in telegraphy or telephony to transmit or send 
the electric impulses over a line wire or con- 
ductor. 

The sending instrument as distinguished 
from the receiving instrument. 

In most telegraphic systems, the transmitting 
instrument consists of various forms of keys for in- 
terrupting or varying the current. In the tele- 
phone the transmitter consists of a diaphragm 
operated by the voice of the speaker. (See Tele- 
phone.) 

Transmitter, Water- Jet Telephone 

— A telephone transmitter consisting of a jet 
of water issuing vertically downwards from a 
small orifice. 

The jet forms a part of the circuit of the re- 
ceiving telephone. In order to reduce its resist- 
ance, the water is rendered acid by the addition 
of sulphuric acid, and a battery of high electro- 
motive force is employed. Since the jet has a 
high resistance, a battery of high resistance can 
be used without inconvenience. 



Tra.] 



533 



[Tro. 



Transposing. — In a system of telephonic 
communication a device for avoiding the bad 
effects of induction by alternately crossing 
equal lengths of consecutive sections of the 
line. (See Connection, Telephonic Cross.) 

Transverse Electromotive Force. — (See 
Force, Electromotive, Transverse.) 

Treatment, Hydro-Carbon, of Carbons 

Exposing carbons, while electrically 

heated to incandescence, to the action of a 
carbonizing gas, vapor or liquid, for the pur- 
pose of rendering them more uniformly elec- 
trically conducting throughout. (See Car- 
bons, Flashing Process for.) 

Tree, Parallel, Circuit (See Cir- 
cuit, Parallel- Tree.) 

Trembling Bell.— (See Bell, Trembling?) 

Trigonometrical. — Of or pertaining to 
trigonometry. (See Trigo?iometry.) 

Trigonometrical Function. — (See Func- 
tion, Trig07iometrical?) 

Trigonometric ally. — In a trigonometrical 
manner. 

Trigonometry. — That branch of mathe- 
matical science which treats of the methods 
of determining the values of the angles and 
sides of a triangle. 

There are in every triangle three sides and 
three angles. If any three of these parts are 
given, except the three angles, the values of the 
remaining parts can be determined by means of 




Fig- 559 > Dynamo Brush Trimmer. 
trigonometry, by what is called the solution of 
the triangle. (See Function, Trigonometrical.) 



Trimmer. — An employee of an electric 
light company who renews the carbons in 
arc lamps. 

Trimmer, Dynamo Brush A de- 
vice for insuring rapid and accurate trimming 
of dynamo brushes. 

The brush trimmer consists of a knife, placed 
as shown in Fig. 559 on a rigid support. The 
brushes are placed under a clamp, and against a 
straight edge, so that a single cut with the knife 
blade insures a clean and true cut. 

Trimming. — A term sometimes applied to 
the act of placing the carbons in an electric 
arc lamp. 

The phrase, carboning a lamp, would appear 
to be preferable to trimming a lamp. 

Triple-Carbon Arc Lamp. — (See Lamp, 
Arc, Triple-Carbon?) 

Tripod Roof Support— (See Support, 
Tripod Roof?) 

Trolley. — A rolling contact wheel that 
moves over the overhead lines provided for a 
line of electric railway cars, and carries off 
the current required to drive the motor car. 

Trolley Crossing. — A device placed at the 
crossing of two trolley wires, by which the 
trolley wheel running on one wire may cross 
the other. 

Such a device can also be made to hold the two 
wires together. 

Trolley Crossing, Insulated A de- 
vice used at the crossing of two trolley wires, 
which insulates the wires from each other, 
but which permits the trolley wheel of one 
line to cross the other trolley line. 

Trolley Cross-Over. — (See Cross-Over, 
Trolley?) 

Trolley. Double The traveling con- 
ductors, which move over the lines of wire in 
any system of electric railways that employs 
two overhead conductors. 

In one form of double trolley a bar of wood 
carries two hangers, separated from each other, 
and furnished with diverging feet, with clips that 
embrace the two conducting wires. These wires 
serve also as the track for the two-wheeled trolley. 
The trolley consists of two plates connected to and 
insulated from each other under the conductors, 



Tro.] 



534 



[Tub. 



and carrying flanged wheels, extending in over 
the conductors. 

Swinging from the axles of the poles are arms, 
which form a bail-like draft loop, with insulated 
material between their lower ends, and furnish 
means for connection with the car motor. In 
order to remove this trolley from the conducting 
wires, these arms are pressed together at points 
between two points of hangers, which allows 
them to pass between the inner ends of the wheel 
axles. 

The trolley cannot be removed from the wires 
except at the end of the track, and it is therefore 
found in practice to be particularly useful in 
mines, where, from the nature of the galleries, the 
trolley wheel is very apt to become detached from 
the trolley wires. 

Trolley, Drop The trolley wheel 

and rod for an electric car which drops away 
from the wire on slipping from the wire, and 
is reset upwards through proper elastic press- 
ure. 
Trolley Fork.— (See Fork, Trolley.) 
Trolley Frog. — (See Frog, Trolley.) 

Trolley Frog, Standard (See Frog, 

Trolley, Standard?) 

Trolley Hanger.— (See Hanger, Trolley?) 

Trolley Pole.— (See Pole, Trolley) 

Trolley Section. — (See Section, Trolley?) 

Trolley, Single A traveling con- 
ductor or wheel which moves over a single 
conductor in a system of electric railways, 
and takes off the current for driving the elec- 
tric motor, in connection with an earth or 
grounded return conductor. 

Trolley Wheel.— (See Wheel, Trolley?) 

Trolley, Wire (See Wire, Trolley) 

True Contact Force. — (See Force, True 
Contact?) 

True Resistance. — (See Resistance, 
True?) 

Trumpet, Electric — An electro- 
magnetic buzzer, the sound of which is 
strengthened by means of a resonator in the 
shape of a trumpet. (See Buzzer, Electric. 
Resonator, Electric?) 



The electric trumpet is used to replace electric 
bells. It gives a louder and more penetrating 
sound than the electric bell. 

Trunking Switch Board. — (See Board, 
Switch, Trunking?) 

Tube, Crookes' A tube containing 

a high vacuum and adapted for showing any 
of the phenomena of the ultra-gaseous state 
of matter. (See Matter, Radiant, or Ultra- 
Gaseous?) 

Tube, Insulating A tube of insu- 
lating material provided for covering a splice 
in an insulated conductor. 

Tube, Mercury Vacuous glass tubes 

in which a flash of light is produced by the 
fall of a small quantity of mercury placed in- 
side it. 

The light is caused by the electricity produced 
by the friction of the mercury in falling against 
the sides of a spiral glass tube placed inside the 
vacuous tube. 

Tube, Plucker A modification of a 

Geissler tube adapted for the study of the 
stratification of the light, and the peculiar- 
ities of the space adjoining the negative elec- 
trode. (See Tubes, Geissler?) 



Tube, Spark 



-A high vacuum tube, 



across which, when the vacuum is sufficiently 
high, the spark from an induction coil will not 
pass. 

A spark tube, connected with incandescent 
lamps while undergoing exhaustion, acts as a 
simple gauge to determine the degree of ex- 
haustion. When an induction coil discharge 
ceases either to pass, or to pass freely, the vacuum 
is considered as sufficient, according to circum- 
stances. 

Tube, Stratification -An exhausted 

glass tube, the residual atmosphere of which 
displays alternate dark and light striae, or 
stratifications, on the passage through it of 
an induction coil discharge. (See Discharge, 
Luminous Effects of?) 

Tubes, Geissler Vacuum tubes of 

glass containing various gases, liquids or 
solids, provided with platinum electrodes, 
passed through and fused into the glass, de- 
signed to show the various luminous effects 



Tub.] 



535 



[Twi. 



of electric discharges through gases at com- 
paratively low pressures. 

Geissler tubes are made of a great variety of 
shapes, and often include tubes, spirals, spheres, 
etc., within other tubes. These enclosed tubes 
are made either of ordinary glass, or of uranium 
glass in order to obtain the effects of fluorescence. 

The vacuum in Geissler tubes is by no means 
what might be called a high vacuum. Indeed, if 
the exhaustion of the tube be pushed too far, 
much of the brilliancy of the luminous effects is 
lost. 

Some of the many forms of Geissler tubes are 
shown in Fig. 560. 




Fig. 560. Geissler Tubes. 

Tubes of Force. — (See Force, Tubes of.) 
Tubes of Induction. — (See Induction, 
Tubes of.) 

Tubes, Tacuuui Glass tubes, from 

which the air has been partially exhausted and 
through which electric discharges are passed 
for the production of luminous effects. (See 
Tubes, Geissler?) 
Tubular Braid. — (See Braid, Tubular.} 
Tumbling Box. — (See Box, Tumbling.) 
Tuning-Fork or Reed Interrupter. — (See 
Interrupter, Timing-Fork. Diterrupter, 
Reed) 

Turn, Ampere A single turn or 

winding in a coil of wire through which one 
ampere passes. 

An ampere-turn is sometimes called an ampere- 
winding. Magneto-motive force in a magnetic 
circuit is proportioned to the number of ampere- 
turns linked with it. The practical unit of mag- 
neto-motive force is X ampere turn = .0796 

ampere turn. Therefore the magneto -motive 



force, m. m. f., is found by multiplying the am- 
pere turns by 4 it or 12.57. 

The number of amperes multiplied by the 
number of windings or turns of wire in a coil give 
the total number of ampere-turns in the coil. 

In a coil of fixed dimensions the magnetizing 
force developed by a given number of ampere-turns 
remains the same as long as the product of the 
amperes and the current remains the same. That 
is to say, the same amount of magnetizing force 
can be obtained by the use of many windings and 
a small current, as in shunt dynamos, or by a few 
turns and a proportionally large current, as in 
series dynamos. (See Machine, Dynamo-Elec- 
tric.) 

Turns, Ampere, Primary — The 

ampere-turns of the primary of an induction 
coil. 
Turns, Ampere, Secondary The 

ampere-turns of the secondary of an induc- 
tion coil. 

Turns, Dead The number of revo- 
lutions a self-exciting dynamo makes before 
it excites itself. 

Turns, Dead, of Armature Wire 

Those turns of the wire on the armature of a 
dynamo-electric machine which produce no 
useful electromotive force or resultant current, 
on the movement of the armature through the 
magnetic field of the machine. 

The wire on the inside of a Gramme or ring 
armature is dead wire, but not dead turns. 

Turns, Series, of Dynamo-Electric Ma- 
chines — The ampere-turns in the 

series circuit of a compound-wound dynamo- 
electric machine. (See Machine, Dyna?no- 
Electric, Compound- Woimd.) 

Turns, Shunt, of Dynamo-Electric Ma- 
chine -The ampere-turns in the shunt 

circuit of a compound-wound dynamo-elec- 
tric machine. (See Machine, Dynamo-Elec- 
tric, Compound- Wound?) 

Turn-Table, Electric A table, suit- 
able for show windows, revolved around a 
vertical axis by means of an electric motor. 

Twig. — A sub-branch. (See Branch, 
Sub) 

Twin Wire.— (See Wire, Twin) 



Twi. 



536 



[Uni, 



Twist in Leads. — (See Leads, Armature, 
Twist in) 

Twisted Bunched Cable. — (See Cable, 
Bunched, Twisted) 

Twisted-Pair Cable.— (See Cable, Twisted- 
Pair) 

Twisting Force. — (See Force, Twisting) 

Two-Fluid Voltaic Cell.— (See Cell, Vol- 
taic, Two-Fluid) 

Two-Point Switch. — (See Switch, Two- 
Point) 

Two, Three, Four, etc., Conductor Cable 

(See Cable, Two, Three, Four, etc., 

Conductor)' 

Two-Way Splice Box. — (See Box, Splice, 
Two- Way) 



Two-Way Switch.— (See Switch, Two- 
Way) 

Type-Printing Telegraph. — (See Teleg- 
raphy, Printing) 

A typewrit- 



Typewriter, Electric — 

ing machine, in which the keys are intended 
to make the contacts only of circuits of 
electro-magnets, by the attraction of the arma- 
tures of which the movements of the type 
levers required for the work of printing are 
effected. 

Electric typewriters secure a uniformity of im- 
pression that is impossible to obtain with hand 
worked machines. They also greatly lessen the 
mechanical labor of writing, (See Dynamo graph.') 



TJ. — A contraction sometimes used for unit. 

Ultra-Gaseous Matter. — (See Matter, 
Radiant, or Ultra-Gaseous) 

Underground Cable.— (See Cable, Under- 
ground) 

Underground Conductor. — (See Con- 
ductor, Underground) 

Undulating Currents. — (See Current, 
Undulating) 

Undulatory Currents. — (See Currents, 
Undulatory) 

Undulatory Discharge. — (See Discharge, 
Undulatory) 

Ungilding Bath.— (See Bath, Ungild- 
ing) 

Unidirectional Discharge. — (See Dis- 
charge, Unidirectional) 

Unidirectional Leak. — (See Leak, Uni- 
directional) 

Uniform Density of Field.— (See Field, 
Uniform Density of) 

Uniform Magnetic Field. — (See Field, 
Magnetic, Uniform) 

Uniform Magnetic Filament. — (See Fila- 
ment, Unifor?n Magnetic) 



Uniform Potential. — (See Potential,. 
Uniform) 

Uniformly Distributed Current. — (See 
Current, Uniformly Distributed) 

Unipolar Armature. — (See Armature, 
Unipolar) 

Unipolar-Electric Bath. — (See Bath, Uni- 
pola r-Electric) 

Unipolar Induction. — (See Induction, 
Unipolar) 

Unit Angle. — (See Angle, Unit. Velocity, 
Angular) 

Unit Angular Telocity.— (See Velocity, 
Angular) 

Unit, B. A. -A term formerly ap- 
plied to the British Association unit of re- 
sistance, or ohm. (See Ohm) 

Unit-Difference of Potential or Electro- 
motive Force (See Potential, Unit 

Difference of) 

Unit, Magnetic, A A term some- 
times used for a line of magnetic force, or 
the amount of magnetism induced in an area 
of one square centimetre at the centre of a 
coil having a diameter of 10 centimetres and 
carrying a current of 7.9578 amperes. 

Unit, Natural, of Electricity (See 

Electricity, Natural Unit of) 



Tni.] 537 [Uni. 

Unit of Acceleration. — (See Acceleration, These units are more frequently called the 

Unit of.) centimetre -gramme-second units. 

Unitof Activity.— (See Activity, UmY of) Vnix% Centimetre-Gramme-Second 

Unit of Current, Absolute (See — A system of units in which the centimetre 

Current, Absolute Unit of.) is adopted for the unit of length, the gramme 

tt •+ * n + t i •» /o f° r the unit of mass, and the second for unit 

Unit of Current, Jacobi's — (See , . 

Curretit, Jacobi's Unit of) 

„..-_.,..,« , „ „ This is the same as the absolute system of 

Unit of Electrical Supply.— (See Supply, units ' 

Unit of, Electrical) 

Unit of Electromotive Force, Absolute Uuits > c - & s - The centimetre- 

(See Force, Electromotive, Absolute gramme-second units. (See Units, Funda- 

Unit of) mental) 

Unit of Electrostatic Capacity.— (See Units, Circular Units based upon 

Capacity, Electrostatic, Unit of) the value of the area of a circle whose diame- 

Unit of Heat.— (See Heat Unit) ter is unit y- 

Unit Of Inductance.— (See Inductance, The advantages possessed by the circular units 

Unit of^\ °^ cross - sect i on ai *i se fr° m tn e fact that in these 

units the areas are equal to the squares of the 

Unit Of Mass.— (See Mass, Unit of) diameter. No necessity exists, therefore, for mul- 

Unit of Photometric Intensity.— (See tiplying by .7854. 

' •*'' Units, Circular (Cross-Sections), Table 

Unit of Power. — (See Power, Unit of) f 

Unit of Pressure, New The Barad. 1 circular mil = -7 8 540 square mil. 

(SeeBarad) " " = .00064514 circular 

Unit of Eesistance.-(See Resistance, millimetre. 

jj - f f\ = .00050669 square 

•^ *' millimetre. 

Unit of Resistance, Absolute (See 1 square mil = 1.2732 circular mils. . 

Resistance, Absolute Unit of ) " " = .00082141 circular 

Unit of Resistance, Jacobi's (See millimetre. 

Resistance, Unit of, Jacobi's) l circular millimetre = 1550. 1 circular mils. 

Unit of Resistance, Matthiessen's I I ' \ \ ' \ Z "^ l^Te ^nt 

(.See Resistance, Unit of, Matthiessen's) metre 

Unit of Resistance, Varley's (See 1 square millimetre .... =1973.6 circular mils. 

Resistance, Unit of, Varley's) " " =1.2732 circular mil- 

_ T .. „ ,. , ., _ T limetres. 

Unit of Telocity, Isew (See Ve- TfJ . , ,. . , . , ., 

_ . __ J K If d, is the diameter of a circle, the area in 

locity y New Unit of) other units fas 

Unit Quantity of Electricity.— (See Elec- If d, is in mils, the area in 

tricity,U7iitQua7itityof) square millimetres . . . . = d 2 X .00050669. 

Unit-Strength of Current.— (See Cur- d ' } n milli metres, area in 

rent, Unit Strength of) S( l uare mils = d2 x I2I 7-4- 

d, in centimetres, area in 

Units, Absolute A system of units square inches = d 2 x 12174. 

based on the centimetre for the unit of length, d, in inches, area in square 

the gramme for the unit of mass, and the centimetres =d 2 x 5.0669. 

second for the unit of time. [Hering.) 



UnL] 



538 



LUni. 



Units, Derived Various units ob- 
tained or derived from the fundamental units 
of Length, L., Mass, M., and Time, T. 

The derived units and their dimensions are as 
follows: 

Area, L s . — The square centimetre. 

Volume, L 3 . — The cubic centimetre. 

Velocity, V. — Unit distance traversed in unit 
time, or 

v=£. (i) 

Acceleration, A. — The rate of change which 
will produce a change of velocity of one centi- 
metre per second. 

V 
A = T (2) 

Substituting in equation (2) the value of V, in 
equation (i), we have 
L 
a _T_L 

I 

Force, F. — The dyne, or the force required to 
act on unit mass in order to impart to it unit 
velocity. 

F = MXA. ( 4 ) 

Substituting the value of A, derived from equa- 
tion (2), we have 

V 
F = MX-- 

Substituting the value of V, derived from equa- 
tion (i), we have 

M L __ ML 
r — TpXTF. — rj>2* (5) 

Work or Energy, W. — The erg, or the work 
done in overcoming unit force through unit dis- 
tance. 

W = r X L=^ xL = ML= 

Power, P. — The unit rate of doing work. 
ML* 

r 7 " ml* 



p=™ 

T 



T 



(6) 



Units, Dimensions of The values 

given to the units of length, L ; mass, M, and 
time, T. (See Units, Derived^) 

Units, Electro-Magnetic A system 

of units derived from the C. G. S. units, em- 



ployed in electro-magnetic measurements. 
(See Units, Centimetre-Gramme- Second.) 

Units based on the attractions or repul- 
sions between two unit magnetic poles at 
unit distance apart. (See Units, Electro- 
static.) 

Units, Electro-Magnetic, Dimensions of 



Current Strength = Intensity of Field X Length = 

Quantity = Current X Time= v/M X L . 
Potential, Difference of Potential, Electromo- 
Work 



tive Force 



Resistance : 



Quantity 



v/M XL* 



Electromotive Force L 
Current = T* 



Capacity = Quantity _T^. 
Potential - L 

Units, Electrostatic Units based 

on the attractions or repulsions of two unit 
charges of electricity at unit distance apart. 

Two systems of electric units are derived from 
the C. G. S. system, viz., the electrostatic and 
electro-magnetic. These units are based respec- 
tively on the force exerted between two quanti- 
ties of electricity and between two magnet poles. 

The electrostatic units embrace the units of 
quantity, potential and capacity. No particular 
names have as yet been adopted for these units. 

Unit of Quantity. — That quantity of electricity 
which will repel an equal quantity of the same 
kind of electricity placed at a distance of one cen- 
timetre from it with the force of one dyne. 

Electrostatic potential, or power of doing elec- 
trostatic work, is measured in units of work, or 
ergs. 

Unit Difference of Potential. — Such a differ- 
ence of potential between two points as requires 
the expenditure of one erg of work to bring up 
a unit of positive electricity from one point to the 
other against the electric force. 

Unit of Capacity. — Such a capacity of conduc- 
tor as will take a charge of one unit of electricity 
when the potential is unity. 

The ratio between the inductive capacity of a 
substance and that of air, measured under pre- 



Uni.] 



539 



[Uni. 



cisely similar conditions, is called the specific in- 
ductive capacity. 

The specific inductive capacity is obtained by 
comparing the capacity of a condenser filled with 
the particular substance and the capacity of the 
same condenser when filled with air. The spe- 
cific inductive capacity of air is taken as unity. 

Units, Electrostatic, Dimensions of 



Quantity = ^Force x (Distance) 2 = v/F X L* = 



m 1 ^ ii 



v^M X D 



Current = Q uantit y 



T 



1*1* 



f M X L 3 



Potential = 



Resistance = 



Time 

Work 
Quantity 
Potential 
Current 



M? I> _ y/Mxr 

T — T 

T 

. T-l t = — • 



L. 



A Simple Ratio or Number. 



Capacity = Q™°tity 
Potential 

Specific Inductive Capacity 

One Quantity 
Another Quantity 
Electromotive Intensity = 

Force = M | L i T \ = v^MxL 
Quantity T 

The fractional and negative exponents used 
above are merely convenient methods of express- 
ing the extraction of roots and division respec- 
tively by the quantity represented by these expo- 
nents. 

Units, Fundamental The units of 

length, time and mass, to which all other 
quantities can be referred. 

The unit of length is now generally taken as 
the centimetre, the unit of time as the second, and 
the unit of mass as the gramme. These form a 
system of measurement known as the centimetre- 
gramme-second system, or the C. G. S. system, or 
absolute system. (See Units, Derived.) 

The dimensions of the fundamental units are 
designated thus: 

Length = L. 
Mass = M. 
Time = T. 



quantity of heat required to raise a given 
weight or quantity of a substance, generally 
water, one degree. 

The principal heat units are the English heat 
unit, the greater and smaller calorie and the 
joule. (See Calorie. Joule.) 

The following table gives the values of some of the prin- 
cipal heat units : 

1 gram, centigrade, .001 kilogram centigrade. 

1 pound Fahrenheit, 1,047.03 joules. 

" 772. foot-pounds. 

" 106.731 kilogram metres. 

" ^55556 pound centigrade. 

" .25200 kilogram centigrade. 

*' .29084 watt-hours. 

" .0003953 metric horse-power. 

" .0003899 horse-power hours. 

1 pound centigrade, 1,884.66 joules. 

" 1,389.6 foot-pounds. 

" 192. 116 kilogram metres. 

" 1.800 pound Fahrenheit. 

" 4536 kilogram centigrade. 

" -52352 watt-hour. 

" .0007115 metric horse-power 

hour. 

" .0007018 horse-power hour. 

1 kilogram centigrade, 4,154.95 joules. 

" 31063.5 foot-pounds. 

423.54 kilogram metres. 

" 3.9683 pound Fahrenheit. 

" 2.2046 pound centigrade. 

" 1-1542 watt-hour. 

" .001569 metric horse-power 

hour. 
.0015472 horse-power hour. 
— Hering. 

— Units based on 



Units, Magnetic 



Units, Heat 



Units based on the 



the force exerted between two magnet poles. 

Unit strength of a magnetic pole is such a 
magnetic strength of pole that repels another 
magnetic pole of equal strength placed at 
unit distance with unit force, or with the 
force of one dyne. 

Magnetic Potential. — Is the power of doing 
work possessed by a magnetic pole. 

Magnetic potential is measured like electro- 
static potential in units of work or in ergs. 

Mag7ietic Potential, Unit Difference of. — Such 
a difference of magnetic potential between two 
points that requires the expenditure of one erg of 
work to bring a magnetic pole of unit strength 
from one to the other. 

Unit Intensity of Magnetic Field. — Such an 
intensity of magnetic field as acts on a north or 
south-seeking pole of unit strength with the force 
of one dyne. 



Uni.] 



540 



[Upr. 



Units, Magnetic, Dimensions of 

Strength of Pole, or 
Quantity of Magnetism 

= v/ Force X (Distance) s = y/ML 3 

T 
Magnetic Potential 

y /MxL 
T ' 

_ v 7 ^" 
Intensity of Field 



Work 
Strength of Pole 

Force 



Strength of Pole T X v 7 L 

Units, Practical Multiples or frac- 
tions of the absolute or centimetre-gramme- 
second units. 

The practical units have been introduced be- 
cause the absolute units are either too small or 
too large for actual use. 

Electromotive Force. — The Volt = 100,000,. 
000 C. G. S. or absolute units, that is, io 8 abso- 
lute units of resistance. (See Volt.) 

Resistance.— The Ohm = 1,000,000,000 abso- 
lute units of electromotive force, or io 9 absolute 
units. (See Ohm.) 

Current. — The Ampere = ^ absolute unit of 
current. (See Ampere. ) 

Quantity. — The Coulomb = J^ absolute unit of 
quantity, of the electro-magnetic system. (See 
Coulomb.) 

Capacity. — The Farad = ■ abso- 

* J 1,000,000,000 

lute unit of capacity, or io 9 units of capacity. 

(See Farad. Henry. Wait. Joule.) 

Units, Proposed New The follow- 
ing units and terms have recently been pro- 
posed by Oliver Heaviside. 

Some of these have been generally adopted. 

Conductance. — Capacity for conducting elec- 
tricity. 

Numerically, the ratio, in absolute measure, ot 
the current strength to the total electromotive 
force in a circuit of uniform flow. A quantity 
with the nature of a slowness or reciprocal to a 
velocity. The practical unit is called the mho. 

Conductivity. — Conductance per unit volume. 

Elastance. — Capacity of a dielectric for oppos- 
ing electric charge or displacement. 

"Numerically, the ratio, in absolute measure, 
of the difference of potential in an electrostatic cir- 
cuit to the total charge or displacement therein 
produced. The reciprocal of permittance and a 
quantity of the inverse nature of a length." 

" Elastivity. — Elastance per unit volume of di- 
electric. ' ' 

Impedance. — Capacity for opposing the variable 
flow of electricitv-T- 



" Numerically , in the absolute measure, the 
ratio of the total electromotive force to the cur- 
rent strength at any instant in a circuit of a vari- 
able flow. A quantity with the nature of a 
velocity and in any circuit always greater than 
the resistance." 

"Inductance. — Capacity for magnetic induc- 
tion." 

"Numerically, in absolute measure, the num- 
ber of unit lines of magnetic force linked with a 
circuit traversed by the unit current strength. 
Sometimes alluded to as the co-efficient of self-in- 
duction. A quantity of the nature of a length." 

" Inductivity. — Specific capacity for magnetic 
induction. 

' ' The numerical ratio of the induction in a 
medium to the induction producing it." 

Permittance. — Electrostatic capacity. Capa- 
city of a dielectric for assisting charge or displace- 
ment. 

"Numerically, the ratio, in absolute measure, 
of the total charge or displacement in the electro- 
static circuit, to the difference of potential pro- 
ducing ito A quantity with the nature of a 
length." 

" Permittivity . — The numerical ratio of the 
permittance of a dielectric to that of air. 

" Also known as specific inductive capacity." 

" Reluctajice. — Capacity for opposing mag- 
netic induction. 

"Numerically, the ratio, in absolute measure, 
of the magneto-motive force in a magnetic cir- 
cuit to the total induction therein produced. A 
quantity with the nature of the reciprocal of a 
length. Sometimes described as magnetic resist- 
ance." 

Reluctancy or Reluctivity . — Reluctance per unit 
volume. 

"Sometimes described as specific magnetic re- 
sistance. A numeric, the reciprocal of induc- 
tivity.*' 

4 ' Resistance. — Capacity for opposing the 
steady flow of electricity. 

"Numerically, in absolute measure, the ratio 
of the total electromotive force to the current 
strength in a circuit of uniform flow. A quantity 
with the nature of a velocity. The practical unit 
is called the ohm." 

"Resistivity. — Resistance per unit volume; 
sometimes alluded to as specific resistance." 

Universal Discharger. — (See Discharger, 
Universal.) 

Upright Galvanometer.— (See Galva- 
nometer, Upright.) 



Tac. 



541 



[Tar. 



T. — A contraction sometimes used for volt. 
T. — A contraction sometimes used for ve- 



locity. 

T. — A contraction sometimes used for vol- 
ume. 

Y. A. — A contraction sometimes used for 
voltaic alternative. (See Alternatives, Vol- 
taic?) 

Vacuum, Absolute A space from 

which all traces of residual gas have been 
removed. 

A term sometimes loosely applied to a par- 
tial vacuum. 

It is doubtful whether an absolute vacuum is 
attainable by any physical means. 

Vacuum, Hig'h A space from which 

nearly all traces of air or residual gas have 
been removed. 

Such a vacuum that the length of the 
mean free path of the molecules of the residual 
atmosphere is equal to or exceeds the di- 
mensions of the containing vessel. (See 
Layer, Crookes '.) 

Vacuum, Low Such a vacuum that 

the mean free path of the molecules of the 
residual gas is small as compared with the 
dimensions of the containing vessel. (See 
Tubes, Geissler.) 

In a high vacuum groups ot molecules can 
move across the containing vessel without meet- 
ing other groups of molecules. In a low vacuum 
such a group of molecules would be broken up by 
collision against other groups before reaching 
the other side of the vessel. 

Vacuum, Partial A name some- 
times applied to a low vacuum. (See Vac- 
uum, Low.) 

Vacuum, Torricellian The vacuum 

which exists above the surface of the mercury 
in a barometer tube or other vessel over thirty 
inches in vertical height. 

The Torricellian vicuum is high'only when the 
mercury has been carefully boiled and the tube 
or other vessel vigorously heated, so as to thor- 



oughly drive out the moisture and adherent film 
of air. 

Vacuum Tubes. — (See Tubes, Vacuum) 
Valency. — The worth or value of a chemi- 
cal atom as regards its power of displacing 
other atoms in chemical compounds. (See 
Atomicity) 

The worth or valency of 'an atom of oxygen is 
twice as great as that of hydrogen, since one 
atom of oxygen is able to replace two hydrogen 
atoms in chemical combinations. 

Valve, Electric — An electrically 

controlled or operated valve. 

In systems of electro-pneumatic signals, gaseous 
or liquid pressure controlled by electrically oper- 
ated valves is employed to move signals, ring 
bells, control water and air valves, or to perform 
other similar work. 

Vapor Globe of Incandescent Lamp. — 

(See Globe, Vapor, of Incandescent Lamp) 

Variable Inductance.— (See Inductance, 
Variable) 
Variable Period of Electric Current. — 

(See Curre?it, Variable Period of) 
Variable Resistance. — (See Resistance, 

Variable) 
Variable Resistance, Automatic 

(See Resistance, Variable, Automatic) 

Variable Resistance, Non-Automatic 

— (See Resistance, Variable, Non-Auto- 
matic) 

Variable State of Charge of Telegraph 
Line. — (See State, Variable, of Charge of 
Telegraph Line) 

Variation, Angle of The angle 

which measures the deviation of the magnetic 
needle to the east or west of the true geo- 
graphic north. 

The angle of declination of the magnetic 
needle. (See Declination, Angle of) 

Variation, Annual — An approxi- 
mately regular variation in the magnetic 



Tar.] 



542 



[VeL 



needle which occurs at different seasons of 
the year. 

Variation Chart or Map. — (See Map or 
Chart, Isogonic.) 



Variation, Cyclical Magnetic Secu- 
lar magnetic variations occurring during 
great cycles of time. (See Variation, 
Secular. Variation, Magnetic.) 

Variation, Diurnal An approxi- 
mately regular variation of the magnetic 
needle, which occurs at different hours of the 
day. (See Declination.) 

Variation, Irregular A variation 

of the magnetic needle which occurs at ir- 
regular intervals. (See Declination.) 



Variation, Magnetic 



— Variations in 
the value of the magnetic declination, or 
inclination, that occur simultaneously over 
all parts of the earth. 

The term is also applied to the magnetic decli- 
nation itself. 

These variations are: 

(i.) Secular, or those occurring at great cycles 
of time. 

(2.) Annual, or those occurring at different 
seasons of the year. 

(3.) Diurnal, or those occurring at different 
hours of the day. 

(4.) Irregular, or those accompanying mag- 
netic storms. The first three are periodical ; the 
last is irregular. (See Declination, Angle of. 
Chart, Inclination.) 

Variation, Secular A variation in 

the magnetic declination which occurs at 
great cycles or intervals of time. (See Dec- 
lination.) 

Varieties of Circuits. — (See Circuits, 
Varieties of.) 

Variometer, Magnetic An instru- 
ment for comparing the horizontal compo- 
nent of the earth's magnetism in different 
localities. 



Varnish, Electric 



-A varnish formed 



thoroughly dried surface and afterwards hard- 
ened by baking, forms an excellent varnish. 

Varnish, Stopping-Off A varnish 

used in electro-plating to cover portions 
which are not to receive the metallic coat- 
ing. 

A good stoppmg-off varnish is made by mixing 
together 10 parts of rosin, 6 parts of beeswax, 
4 parts of sealing-wax and 3 parts of rouge, dis- 
solved in turpentine. (See Stopping-Off.) 



Vat, Depositing 



-The vat in which 



of any good insulating material. 
Shellac dissolved in alcohol, applied to a 



the process of electro-plating is carried on. 
(See Plating, Electro?) 

The depositing vat contains the plating liquid, 
the metallic anode and the object to be plated. 

Vegetation, Effects of Electricity on 

Most vegetable fibres contract when 

an electric current is passed through them 
while on the living plant. 

Some experiments appear to show that electric 
charges and currents hasten the germination and 
growth of certain plants. Other experiments 
seem to show that under certain circumstances 
electric currents retard plant growth. The di- 
rection of the currents is probably of main im- 
portance. 

Velocimeter. — Any apparatus for measur- 
ing the speed of a machine. 

Velocity, Angular The velocity of 

a body moving in a circular path, measured, 
not as usual, by the length of its path divided 
by the time, but with reference to the angle 
it subtends and to the length of the radius. 

Unit angle is that angle subtended by a part 
of the circumference equal to the length of the 
radius, or 57 degrees 17 minutes 44 seconds .8 
nearly . — [Daniell. ) 

Unit angular velocity is the velocity under 
which a particle moving in a circular path, whose 
radius equals unity, would traverse unit angle in 
unit time. 

Velocity, New Unit of The kine. 

(See Kine.) 

Velocity of Discharge. — (See Discharge, 
Velocity of.) 

Velocity Ratio. — (See Ratio, Velocity.) 



Ten.] 



543 



[Tib. 



Ventilation of Armature. — (See Arma- 
ture, Ventilation of.) 

Vernier. — A device for the more accurate 
measurement of small differences of length 
than can be detected by the eye alone, by 
means of the direct reading of the position 
of a mark on a sliding scale. 

The sliding scale is called the vernier. There 
are a variety of vernier scales in use. 

Vertical Component of Earth's Magnet- 
ism. — (See Component, Vertical, of Earth's 
Magnetism.) 

Vertical Electrostatic Voltmeter. — (See 
Voltmeter, Vertical, Electrostatic) 

Verticity, Poles of, Magnetic The 

earth's magnetic poles, as determined by 
means of the dipping needle. 

The point of the north where the angle of dip 
is 90 degrees. (See Map or Chart, Inclination.) 

Vibrating-.— Moving to-and-f ro. 

Vibrating* Bell. — (See Bell, Vibrating.) 

Vibrating* Contact. — (See Contact, Vibrat- 
ing.) 

Vibration. — A to-and-fro motion of the 
particles of an elastic medium. (See Wave.) 

Vibration or Wave, Amplitude of 

The ratio that exists in a wave between 
the degree of condensation and rarefaction 
of the medium in which the wave is propa- 
gated. 

The amplitude of a wave is dependent on the 
amount of energy charged on the medium in 
which the vibration or wave is produced. 

A vibration or wave is a to-and-fro motion pro- 
duced in an elastic material or medium by the 
action of energy thereon. Sound, light and heat 
are subjectively effects produced by the action of 
vibrations or waves, which in the case of sound 
are set up in the air, and, in that of light and 
heat, in a highly tenuous medium called the lumi- 
niferous ether. Objectively they are the waves 
themselves. 

As the amplitude of a sound wave increases, the 
loudness or intensity of the sound increases. As 
the amplitude of the ether wave increases, the 
brilliancy of the light or the intensity of the light 
or heat increases. 



Let A C, Fig. 561 represent an elastic cord or 
string tightly stretched between A and C. If 
the string be plucked by the finger, it will move 
to-and-fro, as shown by the dotted lines. Each 
to-and-fro motion is called a vibration. The 



,--—"■ — D 



Fig. j6r. Amplitude of Wave. 

vertical distance B D, or B E, represents the 
amplitude of the vibration, and the sound pro- 
duced is louder, the greater the amount of energy 
with which the string has been plucked, or, in 
other words, the greater the value of B D, or 
B E. 

Vibrations assume various forms in solid or 
fluid media, but in all cases the amplitude will 
increase with the increase in the energy that 
causes the vibration. 

Vibration Period.— (See Period, Vibra- 
tion.) 

Vibration, Period of — The time 

occupied in executing one complete vibration 
or motion to-and-fro. 

Vibration, Phase of The position 

of the particles in motion in a wave or vibra- 
tion at any instant of time during the wave 
period, as compared with a zero line, or aline 
passing through their mean or middle position. 

Vibrations, Isochronous — Vibra- 
tions which perform their to-and-fro motions 
on either side of the position of rest in equal 
times. 

The vibrations of a pendulum are practically 
isochronous, no matter what the amplitude of the 
swing may be, that is, whether the pendulum 
swings through a large arc or a small arc, pro- 
vided this arc be not very great. 

All vibrations that produce musical sounds may 
be regarded as isochronous; that is, in any case, 
the time required to complete a to-and-fro motion 
is the same at the beginning when the sound is 
loud, as at the end, when it is faint. 

Vibrations, Sympathetic —Vibra- 
tions set up in bodies by waves of exactly the 
same wave rate as those produced by the 
vibrating body. 

The pitch or tone of the note produced by the 
body set into sympathetic vibration, is exactly the 



Vib.] 



544 



[Vol. 



same as the pitch or tone of the exciting waves or 
vibrations. 

Hertz's experiments show that sympathetic vi- 
brations are excited by electro-magnetic waves* 
(See Electricity, Hertz's Theory of Electro-Mag- 
netic Radiations or Waves.) 

Vibrations, Sympathetic, Electrical 

— Vibrations set up in circuits, by the effect 
of pulses in neighboring circuits, that are of 
exactly the same mean length. 

Titrations, Synchronous — Vibra- 
tions that are performed not only in the same 
time as one another, but which pass through 
the same portions of their to-and-fro move- 
ment at the same time. 



Vibrator, Electro-Magnetic 



A 



lever, or arm, automatically moved to-and- 
fro by the alternate attractions of an electro- 
magnet and an opposing spring, or by the 
successive action of two electro-magnets. 

In either case the movement of the lever is 
utilized to permit the action of first one and then 
the other device. Automatic or trembling bells 
are operated by means of an electro magnetic 
vibrator. 

Tillari Critical Point— A term proposed 
by Sir William Thomson for that strength of 
magnetic field at which the reversal of the 
effects of tension occurs. 

Both magnetic susceptibility and permeability 
are affected by mechanical stress, vibration and 
changes of temperature. In a weak magnetic 
field the susceptibility of iron wire is increased by 
longitudinal tension, while in a strong field it 
may be decreased. The particular strength of 
field at which the reversal occurs is called the 
Villari critical point. 

Tiscosity, Magnetic — That prop- 
erty of iron or other paramagnetic substance 
in virtue of which a certain time is required 
before a given magnetizing force can pro- 
duce its effects. (See Hysteresis, Viscous?) 

Viscous Hysteresis.— (See Hysteresis, 
Viscous?) 

Tis-Tiva. — The energy stored in a moving 
body, and therefore the measure of the amount 
of work that must be performed in order to 
bring a moving body to rest. 



If M, is the mass and V, the velocity 
The Vis- Viva = MYf 

2 

Titreous Electricity. — (See Electricity, 
Vitreous?) 

Titrite. — An insulating substance. 

Volatilization, Electric A term 

sometimes used instead of electric evapora- 
tion. (See Evaporation, Electric) 

Tolcanic Lightning". — (See Lightning, 
Volcanic?) 

Tolt. — The practical unit of electro- 
motive force. 

Such an electromotive force as is induced 
in a conductor which cuts lines of magnetic 
force at the rate of 100,000,000 per sec. 

Such an electromotive force as would 
cause a current of one ampere to flow against 
the resistance of one ohm. 

Such an electromotive force as would 
charge a condenser of the capacity of one 
farad with a quantity of electricity equal to 
one coulomb. 

10 s absolute electro-magnetic units of elec- 
tromotive force. 

Volt-Ammeter. — A wattmeter. 

A variety of galvanometer capable of di- 
rectly measuring the product of the difference 
of potential and the amperes. (See Watt- 
meter?) 

Volt Ampere.— A watt. (See Watt?) 

Volt-Coulomb. — The unit of electric work. 

The joule. (See Joule.) 

Volt, Mega One million volts. 

Volt, Micro The one-millionth of a 

volt. 

Voltage. — This term is now very com- 
monly used for either the electromotive force 
or difference of potential of any part of a 
circuit as determined by the reading of a 
voltmeter placed in that part of the circuit. 

Voltage, Terminal The electro- 
motive force expressed in volts of a dynamo 
or other electric source, as indicated by a 
voltmeter placed across its terminals. 

The terminal voltage is greater than that on 
the leads or conductors at some distance from 



Yol.] 



545 



[Yol 



the source and less than that generated by the 
source. 

There is an exception to this general statement 
in the case of certain leads connected wiih an 
a'ternating dynamo- electric machine. (See Ef- 
fect, Ferranti.) 

Voltaic Arc— (See Arc, Voltaic?) 

Voltaic Battery. — (See Battery, Voltaic?) 

Voltaic Battery Indicator. — (See Indica- 
tor, Voltaic Battery.) 

Voltaic Battery Protector.— (See Pro- 
tector, Voltaic Battery?) 

Voltaic Cell.— (See Cell, Voltaic?) 

Voltaic Cell, Bichromate — (See 

Cell, Voltaic, Bichromate.) 

Voltaic Cell, Bimseii's (See Cell, 

Voltaic, Buns en's.) 

Voltaic Cell, Callaud's (See Cell, 

Voltaic, Callaud's.) 

Voltaic Cell, Capacity of Polarization of 

(See Cell, Voltaic, Capacity of Polar - 

ization of.) 

Voltaic Cell, Closed-Circuit (See 

Cell, Voltaic, Closed-Circuit .) 

Voltaic Cell, Contact Theory of 

(See Cell, Voltaic, Contact Theory of.) 

Voltaic Cell, Creeping" of (See 

Cell, Voltaic, Creeping in.) 

Voltaic Cell, Darnell's (See Cell, 

Voltaic, Daniell's.) 

Voltaic Cell, Double-Fluid (See 

Cell, Voltaic, Double-Fluid?) 

Voltaic Cell, Dry (See Cell, Vol- 
taic, Dry.) 

Voltaic Cell, Gravity (See Cell, 

Voltaic, Gravity.) 

Voltaic Cell, Greuet (See Cell, 

Voltaic, Grenet.) 

Voltaic Cell, Grove (See Cell, Vol- 
taic, Grove?) 

Voltaic Cell, Leclanche (See Cell, 

Voltaic, Leclanche?) 

Voltaic Cell, Local Action of (See 

Action, Local, of Voltaic Cell.) 



Voltaic Cell, Meiding-er (See Cell, 

Voltaic, Meidinger.) 

Voltaic Cell, Negative Plate of 

(See Plate, Negative, of Voltaic Cell.) 

Voltaic Cell, Open-Circuit (See 

Cell, Voltaic, Open-Circuit.) 

Voltaic Cell, Pog-gendorff —(See 

Cell, Voltaic, Poggendorff?) 

Voltaic Cell, Polarization of (See 

Cell, Voltaic, Polarization of.) 

Voltaic Cell, Positive Plate of 

(See Plate, Positive, of Voltaic Cell?) 

Voltaic Cell, Siemens-Halske — 

(See Cell, Voltaic, Siemens-Halske?) 

Voltaic Cell, Simple (See Cell, 

Voltaic, Simple?) 

Voltaic Cell, Single-Fluid (See 

Cell, Voltaic, Single-Fluid?) 

Voltaic Cell, Smee (See Cell, Vol- 
taic, Smee.) 

Voltaic Cell, Standard (See Cell, 

Voltaic, Standard?) 

Voltaic Cell, Standard, Clark's 

(See Cell, Voltaic, Standard, Clark's.) 

Voltaic Cell, Standard, Clark's, Ray- 

leigh's Form of (See Cell, Voltaic, 

Standard, Rayleigh's Form of Clark's?) 

Voltaic Cell, Standard, Fleming's 

— (See Cell, Voltaic, Standard, Fleming's.) 

Voltaic Cell, Standard, Lodg'e's 

(See Cell, Voltaic, Standard, Lodge's.) 

Voltaic Cell, Standard, Sir Wm. Thom- 
son's (See Cell, Voltaic, Standard, 

Sir William Thomson 's.) 

Voltaic Cell, Standardizing- (See 

Cell, Voltaic, Standardizing a.) 

Voltaic Cell, Two-Fluid (See Cell, 

Voltaic, Two-Fluid.) 

Voltaic Cell, Water (See Cell, 

Voltaic, Water.) 

Voltaic Cell, Zinc-Carbon (See 

Cell, Voltaic, Zinc-Carbon.) 

Voltaic Cell, Zinc-Copper (See 

Cell, Voltaic, Zinc-Copper?) 

Voltaic Circle. — (See Circle, Voltaic?) 



Tol.] 



546 



[Tol. 



Toltaic Circuit. — (See Circuit, Voltaic?) 
Toltaic Couple. — (See Couple, Voltaic.) 
Voltaic Effect— (See Effect, Voltaic) 
Voltaic Electricity. — (See Electricity, 
Voltaic.) 

Voltaic Element. — (See Eleme?it, Vol- 
taic) 

Voltaic or Current Induction. — (See In- 
duction, Voltaic) 

Voltameter. — An electrolytic cell em- 
ployed for measuring the quantity of the 
electric current passing through it by the 
amount of chemical decomposition effected 
in a given time. 

Various electrolytes are employed in voltam- 
eters, such as aqueous solutions of sulphuric 
acid, copper sulphate, or other metallic salts. 

In the sulphuric acid voltameter shown in Fig. 
562, the lattery terminals are connected with pla- 
tinum electrodes, immersed in water slightly acidu- 
lated with sulphuric acid, and placed inside glass 
tubes, also filled with acidulated water. On the 
passage of the current hydrogen appears at the 
kathode, and oxygen at the anode, in nearly the 
proportion of two volumes to one. (See Ozone.) 




Fig. 562. A Szdphuric Acid Voltameter. 

In the case of water containing sulphuric acid 
{hydrogen sulphate) the decomposition would ap- 
pear to be that of the sulphuric acid rather than 
that of the water. The reaction is as follows: 
H 2 S0 4 =H, + S0 4 . 

The hydrogen appears at the electro negative 
terminal or kathode. The S0 4 appears at the 
electro positive terminal or anode, but combines 
with one molecule of water, thus, S0 4 -f- H 2 = 
H s S0 4 -(- O, gaseous oxygen being driven off at 
the anode. 

Voltameters are not as well suited as galva- 
nometers for the measurement of electric currents, 
because a certain electromotive force must be 
reached before electrolysis is effected. 



The voltameter in reality measures the cou- 
lombs, and, therefore, is valuable as a current 
measurer only when the current is constant. 

Coulomb-meter would, therefore, be the pref- 
erable term. 

Then, again, time is required to produce the 
results, and considerable difficulty is experienced 
in maintaining the current strength constant, 
either on account of variations in the electro- 
motive force of the source, or of variations in the 
resistance of the voltameter. 

Voltameter, Copper A voltameter 

in which the quantity of the current passing 
is determined by the weight of copper de- 
posited. 

A current, the strength of which is constant, is 
passed through the voltameter for a given time. 
The kathode, preferably of platinum, is thor- 
oughly cleaned and dried with a current of heated 
air and accurately weighed before and after. 
The current strength is then deduced from the 
increase in weight and the time. 

A galvanometer is kept in the circuit of the 
battery and voltameter. If a Daniell battery is 
used, it should be kept on closed-circuit through 
a resistance for some time before use, in order to 
insure normal current. 

It will be noticed that the indications of this 
voltameter are based on the gain in weight of the 
kathode. The loss in weight of the anode is mis- 
leading, owing to secondary chemical action and 
disintegration. 

Voltameter, Gas — A term sometimes 

used for volume voltameter. (See Voltam- 
eter, Volume.) 

Voltameter, Siemens' Differential 

A form of voltameter employed by Sir Wil- 
liam Siemens for determining the resistance of 
the platinum spiral used in his electric pyrom- 
eter. (See Pyrometer, Siemens' Electric) 

Two separate voltameter tubes, provided with 
platinum electrodes and filled with dilute sulphu- 
ric acid, are provided with carefully graduated 
tubes to determine the volume of the decomposed 
gases. (See Voltameter, Volume.) 

A current from a battery is divided by a suit- 
able commutator into two circuits connected re- 
spectively with the two voltameter tubes. In one 
of these circuits a known resistance is placed, in 
the other the resistance to be measured, i. e. , the 
platinum coil used in the electric pyrometer. 



Vol.] 



547 



[Vol. 



Voltameter, Silver A voltameter 

in which the quantity of the current passing 
is determined by the weight of silver de- 
posited. 

A solution of silver nitrate is used as the elec- 
trolytic liquid. When the current to be measured 
is strong the strength of the silver nitrate solution 
is made stronger. 



Voltameter, Volume 



■A voltameter 



in which the quantity of the current passing 
is determined by the volume of the gases 
evolved. 

In some forms of volume voltameter in which 
dilute sulphuric acid is electrolyzed, both the 
hydrogen and the oxygen are measured, either 
separately or together. 

In one form of volume voltameter the hydrogen 
only is collected, and thus the error in volum- 
etric determinations arising from the decrease in 
volume from the formation of ozone is avoided. 
The evolved oxygen is isolated from the hydrogen 
by placing a porous jar between the electrodes. 
The negative electrode, is formed of platinum 
fused in the tube, which, for ease of connec- 
tion, is partially filled with mercury. 

The graduated glass tube, in which the hy- 
drogen is collected, is maintained at a nearly con- 
stant temperature by means of a water column. 
A thermometer is provided for corrections of 
volume as affected by temperature. . 

The voltameter contains dilute sulphuric acid, 
about 30 per cent, of acid. 

Voltameter, Weight A voltameter 

in which the quantity of the current passing 
is determined by the difference in the weight 
of the instrument after the circuit has passed 
for a given time. 

A weight voltameter consists essentially of 
platinum electrodes and some means for thor- 
oughly drying the evolved gases. A vessel filled 
with pumice stone moistened with sulphuric acid, 
or a chloride of calcium tube, may be used for this 
purpose. The voltameter is carefully weighed 
before and after the decomposition. The differ- 
ence in weight gives the weight of the sulphuric 
acid decomposed. 

Voltametric Law.— (See Law, Voltamet- 
ricl) 

Voltmeter. — An instrument used for meas- 



uring difference of potential. (See Galva- 
nometer. Potential, Difference of. Volt.) 

A voltmeter may be constructed on the principle 
of a galvanometer, in which case it differs from 
an ammeter, or ampere meter, which measures 
the current, principally in that the resistance 
of its coils is greater, and that in an ampere meter 
the coils are placed in the circuit, while in a volt- 
meter they are placed as a shunt to the circuit. 

The difference of potential is determined from 
the reading of a voltmeter, by the fact that accord- 
ing to Ohm's law, the product of the current and 
the resistance is equal to the electromotive force, 

as C = — from which we obtain CxR = E, 
K. 

In the ordinary operation of a voltmeter, the 
action of the current in passing through a coil of 
insulated wire is to produce a magnetic field, 
which causes the deflection of a magnetic needle. 
Since the resistance of the voltmeter is constant, 
the current passing, and hence the deflection of 
the needle, will vary with the value of E. The 
magnetic field produced by the current deflects 
the magnetic needle against the action of another 
field, which may be either the earth's field, or an 
artificial field produced by a permanent or an 
electro-magnet. Or, it may deflect it against the 
action of a spring, or against the force of gravity 
acting on a weight. There thus arise varieties of 
voltmeters, such as permanent-magnet voltmeters, 
spring voltmeters, and gravity voltmeters. 

Or, the current produced by a given difference 
of potential may be used to heat a wire, and the 
value of the potential difference determined by 
the movement of a needle by the consequent 
expansion of a wire. Cardew's voltmeter operates 
on this principle. (See Voltmeter, Cardew's.) 

Or, the potential difference to be measured 
may be utilized to charge a readily movable 
needle, and thus produce electrostatic attractions 
and repulsions. 

This form of instrument is in reality a form of 
electrometer. (See Electrometer, Quadrant. 
Attraction, Electrostatic. ) 

Voltmeter. Cardew's A form of 

voltmeter in which the potential difference is 
measured by the amount of expansion caused 
by the heat of a current passing through a 
fixed resistance. 

The current produced by the difference of 
potential to be measured is passed through a high 



TolJ 



548 



[YoL 



resistance wire of platinum silver, the expansion of 
which is caused to move a needle across a 
graduated arc. The wire is thin and therefore 
quickly acquires the temperature due to the 
current. 

The Cardew voltmeter possesses an advantage 
of being independent of changes of temperature. 
It is also capable of being used to measure the 
potential difference of alternating currents. 



Voltmeter, Closed-Circuit 



—A volt- 



meter in which the points of the circuit, be- 
tween which the potential difference is to be 
measured, are connected with a closed coil 
or circuit, and which gives indications by 
means of the current so produced in said 
circuit. 

All galvanometer- voltmeters are of the closed- 
circuited type. 

The Weston standard voltmeter shown in Fig. 
563 is a closed-circuit voltmeter. 




Fig. 563. Weston Standard Voltmeter. 

Voltmeter, Electro-Magnetic —A 

form of voltmeter in which the difference 
of potential is measured by the movement of 
a magnetic needle in the field of an electro- 
magnet. (See Voltmeter?) 

Voltmeter, Gravity A form of volt- 
meter in which the potential difference is 
measured by the movement of a magnetic 
needle against the pull of a weight. 

Sir William Thomson's balance instruments are 
used as gravity voltmeters. (See Voltmeter.) 

Voltmeter, Magnetic-Vane A volt- 
meter in which the potential difference is 
measured by the repulsion exerted between a 



fixed and a movable vane of soft iron placed 
within the field of the magnetizing coil. 

A pointer, fixed to the moving vane, serves to 
measure the amount of the repulsion, and conse- 
quently the potential difference producing the 
magnetizing current. The moving vane moves 
under the magnetic repulsion against the action 
of a spring. Discs of copper for damping the 
movements ®f the movable vane, are placed be- 
fore and behind it. 

Voltmeter, Multi-Cellular Electrostatic 

An electrostatic voltmeter in which a 



series of fixed and movable plates are used 
instead of the single pair employed in the 
quadrant electrometer. 

The movable pairs of plates are connected to a 
movable axis and placed vertically above one 
another. To the top of the axis is fixed a light 
aluminium needle or pointer, which moves over a 
graduated scale. A series of fixed plates, suita- 
bly supported and insulated from the ground, 
alternate with the needle plates. 

Voltmeter, Open-Circuit A volt- 
meter in which the points of the circuit where 
potential difference is to be measured are 
connected with an open circuit and give in- 
dications by means of the charges so pro- 
duced. 

Electrometer-voltmeters are of the open-cir^ 
cuited type. 

Voltmeter, Permanent Magnet A 

form of voltmeter in which the difference of 
potential is measured by the movement of a 
magnetic needle under the combined action 
of a coil and a permanent magnet, against the 
pull of a spring. (See Voltmeter?) 

Voltmeter, Reducteur or Resistance for 

(See Reducteur or Resistance for 

Voltmeter?) 

Voltmeter, Vertical Electrostatic 

— A form of voltmeter the needle of which 
moves in a vertical instead of in a horizontal 
plane. 

The construction of the vertical electrostatic 
voltmeter is, in general, similar to that of the 
quadrant electrometer. (See Electrometer, Quad- 
rant.) 



Vol. 



549 



[Wat 



The fixed and movable sectors, the pointer and 
the graduated scale, however, are in vertical in- 
stead of horizontal planes. 




Fig. 364. Vertical hlectrostatic I oltmeter. 

The general arrangement of the vertical elec- 
trostatic voltmeter will be readily understood by 
an inspection of Fig. 564. 

Volume Voltameter. — (See Voltameter, 
Volume?) 
Vortex Atom. — (See Atom, Vortex?) 



Vortex Cylinder. — (See Cylinder, Vor- 
tex^ 

Vortex-Ring* Field. — (See Field, Vortex- 
Ring.) 

Vulcabeston. — An insulating substance 
composed of asbestos and rubber. 

Vulcanite. — A variety of vulcanized rub- 
ber extensively used in the construction of 
electric apparatus. 

Vulcanite is sometimes called ebonite from its 
black color. It is also sometimes called hard 
rubber. 

Though an excellent insulator, vulcanite will 
lose its insulating properties by condensing a film 
of moisture on its surface. This can be best re- 
moved by the careful application of heat. 

The surface is very liable to become covered by 
a film of sulphuric acid, due to the gradual oxi- 
dation of the sulphur. Mere friction will not re- 
move this film, but it may be removed by wash- 
ing with distilled water. A thick coating of var- 
nish will obviate this last defect. 

Vulcanized Fibre. — (See Fibre, Vulcan- 
ized?) 



w 



W. — A contraction sometimes used for 
watt. 

TV. — A contraction sometimes used for 
work. 

TV. — A contraction sometimes used for 
weight. 

Wall Plug-.— (See Plug, Wall) 

Wall Socket.— (See Socket, Wall) 

Ward. — A term proposed by James Thom- 
son for a line and direction in a line. 

Sir William Thomson thus defines the ward of 
magnetization : ' ' The ward in which the magnet- 
izing force urges a portion of the ideal northern 
magnetic matter or northern polarity." 

Waring* Anti-Induction Cable. — (See 
Cable, Anti-I?iduction, Waring?) 

Waste Field. — (See Field, Magnetic, 
Waste?) 

Watches, Demagnetization of —Pro- 



cesses for removing magnetism from, 
watches. 




Fig. S6j- Wright's Demagnetization Apparatus. 

The demagnetization of watches can be readily 
effected by a method proposed by J. J. Wright. 



Wat.] 



550 



LWat. 



The watch is held by its chain and slowly lowered 
to the bottom of a hollow conical coil of wire, and 
then slowly withdrawn from the coil. 

The wire is wound on the coil, as shown in 
Fig. 565, in the shape of a cone, viz.: with a 
single turn at the top, and gradually increasing 
in number of turns towards the bottom. The 
conical coil is connected with a source of rapidly 
alternating currents. 

As the watch is lowered into the coil, it gradu- 
ally becomes more and more powerfully magnet 
ized with alternately opposite polarities, thus 
completely removing any polarity it previously 
possessed. As it is now slowly raised from out 
the hollow cone, this magnetization becomes less 
and less, until, if removed from the conical coil 
while high above its apex, all sensible traces of 
magnetism will have disappeared. 

Watchman's Electric Register. — (See 
Register, Watchman's Electric) 

Water Battery. — (See Battery, Water?) 

Water-Dropping" Accumulator. — (See Ac- 
cumulator, Water-Dropping .) 

Water, Electrolysis of The de- 
composition of water by the passage through 
it of an electric current. 

Water does not appear to conduct electricity 
when pure; it is therefore not quite certain that 
pure water can be electrolytically decomposed. 
The addition of a small quantity of sulphuric 
acid, or of a metallic salt, however, renders its 
electrolysis readily accomplished. (See Vol- 
tameter. ) 

In the opinion of most, it is the sulphuric acid 
that is decomposed rather than the water. 

Water Horse-Power. — The Indian Gov- 
ernment's term for horse-power developed 
by falling water. 

The estimate is made by the following simple 
rule : 15 cubic feet of water falling per second 
through 1 foot equals 1 horse-power. 

Water- Jet Telephone Transmitter.— (See 

Transmitter, Water-Jet Telephone) 

Water - Level Alarm. — (See Alarm, 
Water or Liquid Level) 

Water-Proof Wire.— (See Wire, Water- 
Proof.) 

Water Pyrometer. — (See Pyrometer, 
Stem ens' Wa ter. ) 



Water Rheostat.— (See Rheostat, Water) 

Water Toltaic Cell.— (See Cell, Voltaic, 
Water) 

Watt. — The unit of electric power. The 
volt-ampere. 

The power developed when 44.25 foot- 
pounds of work are done per minute, or 
0.7375 foot-pounds per second. 

The y^g- of a horsepower. 

There are three equations which give the 
value of the watts, viz. : 

(1.) C E = The watts. 

(2.) C 2 R = The watts. 

E 2 

(3.) _ = The watts. 

Where C = the current in amperes ; E = the 
electromotive force in volts, and R = the resist- 
ance in ohms. (See Energy, Electric.) 

Watt Arc— (See Arc, Watt) 

Watt Generator. — (See Generator, Watt?) 

Watt-Hour. — A unit of electric work. 

A term employed to indicate the expendi- 
ture of an electrical power of one watt, for an 
hour. 

Watt-Hour, Kilo The Board of 

Trade unit of work equal to an output of one 
kilo-watt for one hour. 

Watt, Kilo One thousand watts. 

A unit of power sometimes used in stating 
the output of a dynamo. 

A dynamo of 20 units, or a 20-unit machine, is 
one capable of giving an output of 20 kilo-watts. 

Watt-Meter. — A galvanometer by means 
of which the simultaneous measurement of 
the difference of potential and the current 
passing is rendered possible. 

The watt-meter consists of two coils of insu- 
lated wire, one coarse and the other fine, placed 
at right angles to each other as in the ohm-meter, 
only, instead of the currents acting on a sus- 
pended magnetic needle, they act on each other 
as in the electro-dynamometer. 

Watt-Minute. — A unit of electric work. 

An expenditure of electric power of one 
watt for one minute. 

Watt-Second. — A unit of electric work. 

An expenditure of electric power of one 
watt for one second. 



lYeb.] 



551 



[Way 



Wave. — A disturbance in an elastic me- 
dium that is periodic both in space and 
time. 

Wave, Electric An electric disturb- 
ance in an elastic medium that is periodic 
both in space and time. (See Oscillations, 
Electric?) 

Waves, Amplitude of The ampli- 
tude of a vibration. (See Vibration or 
Wave, Amplitude of.) 

Waves, Displacement Waves pro- 
duced in the ether of dielectrics by means of 
•electric displacement. 

The electric stress applied to a dielectric to pro- 
duce electric displacement soon strains it to its 
utmost and no further displacement can occur 
until the direction of the electric power is re- 
versed. A rapidly intermittent current therefore 
can pass through a dielectric and thus produce a 
series of displacement waves. 

Dielectrics, therefore, may be considered as 
pervious or transparent to rapidly intermittent or 
reversed periodic currents, but opaque or imper- 
vious to continuous currents. A condenser inter- 
polated in a telephone circuit does not prevent tele- 
phonic communication, though it does effectually 
stop all continuous currents. 

Waves, Electro-Magnetic Waves 

In the ether that are given off from a circuit 
through which an oscillating discharge is 
passing, or from a magnetic circuit under- 
going variations in magnetic intensity. 

Waves, Electro-Magnetic, Interference 

of Interference effects similar to those 

produced in the case of waves of light, ob- 
served in the case of electro-magnetic radi- 
ations, or waves, in which one system of 
waves, retarded a half wave length behind 
another system of equal wave length and am- 
plitude, results in a complete loss of motion 
of the particles of the ether they tend to 
simultaneously affect. 

In order that complete interference may take 
place, it is necessary 

(i.) That the two waves, or system of waves, 
must meet in opposite phases. That is, that one 
he retarded back of the other one-half a wave 
length, or some odd number of half wave lengths. 

(2.) That the waves simultaneously affect the 



same particles of ether in which they are mov- 
ing. 

(3.) That the energy charged on the ether in 
the shape of waves of electro-magnetic radiation, 
must be equal in the case of each system of waves. 

(4.) That the two systems of waves must have 
the same wave length. 

These conditions, it will be seen, are exactly 
the same as in the case of the interference of 
light. 

It will, of course, be readily understood that if 
electro-magnetic radiations can produce the 
effect of resonance, they must also necessarily 
produce interference effects. 

Waves, Electro-Magnetic, Reflection of 

Reflection of electro-magnetic waves 

similar to the reflection of waves of light. 

In his experiments on electro-magnetic radia- 
tions, Dr. Hertz shows that true reflection of 
electro- magnetic waves occurs from the surfaces 
of certain substances placed in the path of the 
waves. 

In some experiments made in a large room, 
Dr. Hertz obtained undoubted indications of re- 
flection of electro-magnetic waves from the walls 
of the room. 

Waves of Condensation and Rarefaction. 

— The alternate spheres of condensed and 
rarefied air by means of which sound is 
transmitted. (See Waves, Sound.) 

Waves, Sound Waves produced in 

air or other elastic media by the vibrations 
of a sonorous body. (See Sound.) 
Way Line. — (See Line, Way.) 
Weather Cross. — (See Cross, Weather.) 
Weber. — A term formerly employed for 
the unit of electric current, and replaced by 
ampere. (See Ampere?) 

The term weber was originally used to express 
a quantity of electricity equal to what is now 
called one coulomb, and a current designated by 
one weber per second. It was, however, used 
finally as a unit of current. 

Weber. — A term proposed by Clausius and 
Siemens for a magnetic pole of unit strength, 
but not adopted. 

This same term was also employed to desig- 
nate the unit strength of current, now replaced 
by the term ampere. 



Web. 



552 



[Wei. 



Weber's Theory of Diamagnetism. — 

(See Diamagnetism, Weber's Theofy of.) 

Weight, Atomic The relative 

weights of the atoms of elementary sub- 
stances. 

Since the atoms are assumed to be indivisible, 
they must unite or combine as wholes and not 
as parts. Although we cannot determine exactly 
the actual weights of the different elementary 
atoms, yet we can determine their relative weights 
by ascertaining the smallest proportions in which 
any two elements that combine atom for atom 
will unite with each other. Such numbers 
will represent the relative weights of the atoms 
as compared w.th hydrogen. 

Weight Toltameter. — (See Voltameter, 

Weight.) 

Weights and Measures, Metric System 

of A system of weights and measures 

adopted by almost all civilized nations except 
English-speaking, and by the scientific world 
generally. 

For measures of length, the one ten -millionth 
part of the quadrant of a meridian of the earth is 
taken as the unit of length. This unit of length 
is called a metre, and various subdivisions and 
multiples of its length are made on the decimal 
system. 

For a system of weights, the weight of one 
cubic centimetre of pure water at 39 .2 degrees 
Fahr., the temperature of the maximum density of 
water, is taken as the unit of weight. This is 
called a gramme, and various multiples and sub- 
divisions of this unit are made on the decimal 
system. 

The following table of French measures and 
their corresponding English values are taken 
from Deschanel's " Elementary Treatise on 
Natural Philosophy ": 

Length. 

1 millimetre = .03937 inch, or about gV inch. 

1 centimetre = .3937 inch. 

1 decimetre = 3.937 inches. 

1 metre = 39-37 inches = 3.281 feet =s 
I.0936 yard. 

I kilometre = 1093.6 yards, or about f mile. 

Deschanel gives the length of the meter as 
equal to 39.370432 inches. 

U. S. Coast Survey Bull. No. 9 of 1889, gives 
value of meter = 39.36980 inches. Therefore, 
39.37 is probably as accurate as any other figure. 



Area. 
I square millimetre = .00155 square inch. 
1 square centimetre = .155 square inch. 
I square decimetre =15.5 square inches. 
1 square metre =1550 square inches = 10.764 
square feet = 1.196 square yards. 

Volume. 

I cubic millimetre = .000061 cubic inch. 

1 cubic centimetre = .061025 cubic inch. 

1 decimetre = 61.0254 cubic inches. 

Cubic metre = 61025 cubic inches = 35.3156 
cubic feet = 1.308 cubic yards. 

The litre (used for liquids) is the same as the- 
cubic decimetre, and is equal to 1.76 17 pint, or 
.22021 gallon. 

Mass and Weight. 

I milligramme = .01543 grain. 

I gramme = 15.432 grains. 

I kilogramme = 15432.3 grains = 2.205 pounds 
avoirdupois. 

More accurately, the kilogramme is 2.20462125 
pounds. 

Miscellaneous . 

1 gramme per square centimetre = 2.0481 
pounds per square foot. 

1 kilogramme per square centimetre = 14.223 
pounds per square inch. 

1 kilogram metre = 7.2331 foot-pounds. 

I force de cheval — 75 kilogrammetres per 
second, or 542^ foot pounds per second, nearly, 
whereas 1 horse-power (English) = 550 foot- 
pounds per second. 

Conversion of English into French measures ; 
Length. 

1 inch = 2.54 centimetres, nearly. 

1 foot = 30.48 centimetres, nearly. 

1 yard = 91.44 centimetres, nearly. 

1 statute mile = 160933 centimetres, nearly. 

More accurately, I inch = 2.5399772 centi- 
metres. 

Area. 

1 square inch = 6.45 square centimetres, nearly.. 

I square foot = 929 square centimetres, nearly. 

1 square yard = 8361 square centimetres, 
nearly. 

1 square mile = 2.59 X io 1 ° square centimetres r 
nearly. 

Volume. 

1 cubic inch = 16.39 cubic centimetres, nearly. 

1 cubic foot = 283 1 6 cubic centimetres, nearly. 



Wei.] 



553 



[Wei. 



I cubic yard = 764535 cubic centimetres, 
nearly. 

I gallon = 4541 cubic centimetres, nearly. 

Mass. 

1 grain = .0648 gramme, nearly. 
1 ounce avoirdupois = 28.35 grammes, nearly. 
1 pound avoirdupois = 453.6 grammes, nearly. 
1 ton = 1. 016 X 10 6 grammes, nearly. 
More accurately, I pound avoirdupois = 
453.59265 grammes. 

Velocity. 
1 mile per hour = 44-7°4 centimetres per 
second. 

1 kilometre per hour = 27.7 centimetres per 
second. 

Density, 
1 pound per cubic foot = .016019 gramme per 
cubic centimetre. 

62.4 pounds per cubic foot = 1 gramme per 
cubic centimetre. 

Force [assuming g = 981). 
Weight of 1 grain = 63.57 dynes, nearly. 

" I ounce avoirdupois = 2.78 X 10 4 

dynes, nearly. 
" I pound avoirdupois = 4.45 X io 5 

dynes, nearly. 
" I ton = 9.97 X io 8 dynes, nearly. 

11 I gramme = 981 dynes, nearly. 

" I kilogramme ■=■ 9.81 X io 5 dynes, 

nearly. 
Work [assuming g = 981). 
I foot-pound = 1.356 X 10 7 ergs, nearly. 
1 kilogrammetre = 9.81 x io 7 ergs, nearly. 
Work in a second by one theoretical "horse- 
power" = 7.46 X io 9 ergs, nearly. 

Stress [assuming g = 981). 
I pound per square foot = 479 dynes per 
square centimetre, nearly. 

I pound per square inch = 6.9 X io 4 dynes per 
centimetre, nearly. 

I kilogramme per square centimetre = 9.81 
X io 5 dynes per square centimetre, nearly. 

760 millimetres of mercury at o degree C. = 
1. 014 X i°" dynes per square centimetre, nearly. 
30 inches of mercury at o degree C. = 1.163 
X io" 5 dynes per square centimetre, nearly. 

Welding, Electric Effecting the 

welding union of metals by means of heat of 
electric origin. 

In the process of Elihu Thomson, the metals 



are heated to electric incandescence by currents 
obtained from transformers, and are subsequently 
pressed or hammered together. 

Fig. 566, shows the Thomson apparatus for the 
direct system of electric welding. The dynamo 
is combined with the welding apparatus. The 
armature contains two separate windings; one of 
fine wire, in series with the field magnet coils, 
and another of very low resistance, being formed 
of a U-shaped bar of copper. No commutation 
is used, the alternating currents being well 
adapted for heating purposes. The terminals of 
the dynamo are, therefore directly connected to 
the clamps that hold the bar to the welder. 

Fig. 567, shows the apparatus for the Thomson 
Indirect System of Electric Welding. This sys- 
tem is applicable to heavy work, and to cases 
where more than one welding machine is operated 
by the current from a single dynamo. 

In this case a high tension current is converted 




The Thomson Direct Welder. 



into the large welding current employed, by means 
of a suitably proportioned transformer. 

The welding process is the same in either sys- 
tem, and consists essentially in leading the weld- 
ing current into the pieces to be united through 
their points of junction when brought into firm 
end contact. As the current is led across the 
junction the temperature rises sufficiently to soften 
the metal, when the pieces are firmly pressed to- 
gether by the motion of the clamps or holders. 

In the process of Benardos and Olzewski, the 
heat of the voltaic arc is employed for a some- 
what similar purpose, but by a different process. 

In the Thomson system of electric welding 
alternating currents are employed. They are 
either supplied by an alternating current dynamo 
or by a transformer. 

The process of welding is substantially as fol- 



Wei.] 



554 



[Whi, 



lows, viz. : the welding junctions are made slightly 
convex, so as to touch in but one part of their 
opposing faces. They are made to touch near 
their centres and the welding heat is first reached 
near their points of junction. Pressure is then 
applied by means of a screw, lever or hydraulic 
pressure until all the surfaces are at the welding 
temperature. 

This operation requires in practice but a few 
seconds for small work, and at the most but a 




Fig- 5&7' The Thomson Indirect Welder. 

few minutes for larger work. The heating is 
practically local, extending in most cases a dis- 
tance equal to about the diameter of the weld. 

For the purpose of control ing the electro- 
motive force, and thus adapting the same welder to 
different classes of work, when a transformer is 
used, a second transformer provided with a mov- 
able core is placed in series with the first. A 
number of coils of insulated wire are placed in a 
segment of a split-ring laminated-core. These 
may be connected in series or in multiple by a 
switch. An iron armature placed within the 
split ring encloses the annular core and acts as 
the low-resistance secondary. When this is placed 
so as to embrace the primary coils, the difference 
of potential will be different than if moved to one 
side or the other of the ring. 

Welding Transformer. — (See Trans- 
former, Welding?) 

Wheatstone's Electric Balance. — (See 
Balance, Wheatstone's Electric.) 

Wheatstone's Electric Bridge.— (See 

Bridge, Wheatstone's Electric) 
Wheel, Barlow's or Sturgeon's A 

wheel or disc of metal capable of rotation on 
a horizontal axis, that is set into rotation when 
placed between the poles of magnets and 



traversed by a current of electricity from the 
centre to the circumference. 

Wheel, Phonic A wheel maintained 

in synchronous rotation by means of timed 
electric impulses sent over a line, and em- 
ployed in Delany's synchronous multiplex 
telegraphic system. 

The phonic wheel was invented by La Cour, but 
was first put into successful operation in multiplex 
telegraphy by Delany in his system of synchronous 
multiplex telegraphy. (See Telegraphy, Synchron- 
ous Multiplex, Delany^s System.) Delany ob- 
tains the exact synchronism of the phonic wheel 
by means of a series of correcting electric impulses, 
automatically sent over the line on the failure of 
the phonic wheel at either end of the line to ex- 
actly synchronize with that at the other end. 

Wheel, Reaction, Electric A wheel 

driven by the reaction of a convective dis- 
charge. (See Flyer, Electric) 

Wheel, Trolley A metallic wheel 

connected with the trolley pole and moved 
over the trolley wire on the motion of the car 
over the tracks, for the purpose of taking the 
current from the trolley wire by means of 
rolling contact therewith. 

Whirl, Electric A term employed 

to indicate the circular direction of the lines 
of magnetic force surrounding a conductor 
conveying an electric current. (See Field, 
Electro-Magnetic) 

This is more correctly called a magnetic whirl. 
(See Whirl, Magnetic.) 

Whirl, Expanding Magnetic One 

of the magnetic whirls which are sent out 
from a conductor through which a current of 
gradually increasing strength is passing, or 
from a magnet whose magnetism is increas- 
ing. 

The>e magnetic whirls, according to Hertz, 
move outward through free ether with the velo- 
city of light. 

Whirl, Magnetic The lines of mag- 
netic force which surround the circuit of the 
conductor conveying an electric current. 

Whistle, Steam, Automatic Electric 

— A steam whistle, employed on foggy days 
in some systems of railway signals, when the 



Whi.] 



555 



[Wir. 



visual signals cannot be seen, in which the 
passage of the steam through the whistle is 
automatically obtained by the closing of an 
electric contact, or the passage of the loco- 
motive over a certain part of the track. 

White Heat.— (See Heat, White.) 

White Hot.— (See Hot, White.) 

Wimshurst Electrical Machine.— (See 
Machine, Wimshurst Electrical.) 

Wind, Electric — The convection 

stream of air particles produced at the ex- 
tremities of points attached to the surface of 
charged, insulated conductors. (See Con- 
vection, Electric. Flyer, Electric \) 

Windage of Dynamo. — A term proposed 
for the air gap between the armature and the 
pole pieces of a dynamo. 

This term is not much used. 

Winders, Telegraphic Paper Ap- 
paratus for winding or coiling the paper fillets 
used on telegraphic registers. 

When moved by means of a spring they are 
generally styled automatic winders. 

Winding, Ampere A single wind- 
ing or turn through which one ampere passes. 

Ampere-winding is used in the same significa- 
tion as ampere-turn. (See Turn, Ampere.) 

Winding, Bifllar A winding of a 

coil of wire in which, instead of winding the 
wire in one continuous length, it is doubled 
on itself and then wound. 

This method is employed in resistance coils, so 
as to avoid the induction effects. (See Coil, 
Resistance.) 

Winding, Compound, of Dynamo-Electric 

Machine A method of winding in 

which shunt and series coils are placed on 
the field magnets. (See Machine, Dynamo- 
Electric, Compound- Wound.) 



Winding, Series 



—A 



winding of a 
d) namo-electric machine in which a sin- 
gle set of magnetizing coils are placed on the 
field magnets, and connected in series with 
the armature and the external circuit. (See 
Machine, Dynamo-Electric, Series- Wound.) 
Window-Tube Insulation. — (See Insula- 
tor, Window-Tube?) 



Wipe Spark.— (See Spark, Wipe) 

Wiping Contact. — (See Contact, Wiping) 

Wire, Air-Line That portion of a 

circuit which is formed by air-strung wires, in 
contradistinction to the portion which passes 
through underground or submarine cables. 

Wire, Binding, for Telegraph Lines 

— The wire used for securing lines of wire 
conductors to the insulators. 

The line wire rests against the insulators at as 
small an area of contact as possible, generally 
only a mere edge. In order to attach the wire 
to the insulator, and protect the wire from chaf- 
ing, it is secured to the insulator by binding with 
wire. 

Wire, Block A line or wire em- 
ployed in a block system for railroads, con- 
necting a block tower with the next tower 
on each side of it. (See Railroads, Block 
System for.) 

Wire, Braided A conducting wire 

covered with a braiding, as distinguished from 
a wire that is merely wrapped with insulating 
material. 

Cotton or silk is used for braiding. The cov- 
ering is often coated by a layer of some insu- 
lating gum or varnish dissolved in a rapidly 
drying liquid. It is sometimes covered with melted 
paraffine. 



Fig. J 68. Braided Wire. 

A copper wire covered with insulating material 
and then braided is shown in Fig. 568. 

Wire, Calling A wire employed in 

a telegraphic or telephonic system, by means 
of which a subscriber communicates with the 
central office, or one central office communi- 
cates with another. 

This wire is termr d the calling wire in order to 
distinguish from the wire actually used for talking 
or telegraphing. 

Wire, Conductibility and Sizes of 

For tables giving the resistance, size, weight 
per foot, etc., of wire according to some of 
the principal wire gauges see pages 254 and 
256. 



Wir.] 



556 



[Wir. 



Wire, Copper, Hard-Drawn 



-Copper 



wire that is drawn three or four times after 
annealing. 

The drawing subsequent to annealing renders 
the wire hard and elastic, with but a trifling de- 
crease in its conductivity. A hard- drawn wire, 
of course, possesses greater limits of elasticity 
than soft-drawn wire, and, therefore, m the case 
of air lines, permits of the use of a longer distance 
between adjacent poles. 

Wire, Copper, Soft-Drawn Copper 

wire that is softened by annealing after 
drawing. (See Wire, Copper, Hard- 
Drawn.) 

Wire, Dead, of Armature That 

part of the wire on the armature of a dynamo 
which produces no electromotive force or 
resultant current. 

It is called dead because it does not move 
through the field of the machine. 

Wire, Duplex An insulated con- 
ductor containing two separate parallel wires. 

Wire, Earth-Grounded —A wire 

one terminal of which is grounded or put to 
earth, so that the earth forms a part of the 
circuit in which the wire is placed. 

Wire, Feeding" — A term sometimes 

applied to the wire or lead of a multiple cir- 
cuit which feeds the main. 

In a system of electric railroads the feeding 
wires feed the trolley wires. 

Wire Finder. — (See Finder, Wire?) 

Wire, Fuse A readily fusible wire 

employed in a safety catch to open the cir- 
cuit when the current is excessive. (See 
Catch, Safety?) 

Wire Gauge, Yernier (See Gauge, 

Wire, Micrometer?) 

Wire, Grounded (See Ground or 

Earth.) 

Wire, House — In a system of in- 

:andescent electric lighting any conductor 
that is connected with a service conductor 
and leads to the meter in the house. 

Wire, Insulated — Wire covered 

with any insulating material. 



Cotton and silk are generally employed for in- 
sulating purposes, either alone, or in connection 
with various gums, resins, or other materials, 
which are rendered plastic by heat, but which 
solidify on cooling. India rubber, caoutchouc, 
and various mixtures and compounds are also em- 
ployed for the same purpose. 

For most of the purposes of line wires, high in- 
sulating powers, combined with a low specific 
inductive capacity, are required in the insulating 
materials. 

For overhead wires a waterproof covering is 
necessary. In the neighborhood of combustible 
materials, some fireproof covering is desirable. 

Wire, Lead A lead fuse wire. 

Wire, Line In telegraphy the wire 

that connects the different stations with one 
another. 

In bell and annunciator circuits, the term line 
wire is sometimes applied to all circuits other 
than the main line. 

In arc-light circuits the term line wire is applied 
to the entire metallic circuit, io which the lamps 
are connected in series. 

Wire, Main The principal wire. 

In any system of bell circuits the main wire is 
the wire which runs from one pole of the battery 
to one of the springs of all the pushes, in distinc- 
tion from ihe line wires, or the rest of the wires 
in the battery circuit. 

Wire, Message A line or wire em- 
ployed in a block system for railroads, ex- 
tending along the road and used for local 
traffic or business. (See Railroads, Block 
System for.) 

Wire, Negative A term sometimes 

applied to that wire of a parallel circuit which 
is connected to the negative pole of a source. 

Wire, Neutral The middle wire of 

a three-wire system of electric distribution. 

Wire, Omnibus An onmibus bar. 

(See Bars, Omnibus?) 

A bus bar or wire. (See Wires, Bus.) 

Wire, Paraffined Wire wrapped or 

braided with some textile material and after- 
wards coated with paraffine. 

The term paraffined wire is sometimes limited 
to a wrapped wire that is afterwards paraffine 
coated. 



Wir.] 



557 



[Wir. 



Wire, Positive The wire or con- 
ductor connected to the positive pole or ter- 
minal of any electric source. 

Wire, Potentiometer The wire of 

a potentiometer which has been calibrated in 
order to measure the drop of potential in any 
circuit. (See Potentiometer^) 

Wire, Return The wire or con- 
ductor by means of which the current returns 
to the electric source after having passed 
through the electro-receptive devices. (See 
Sources, Electric. Device, Electro-Recep- 
tive^) 

Wire, Shade Guard (See Gtcard f 

Wire Shade.) 

Wire, Slide — A wire of uniform 

diameter employed in Wheatstone's electric 
bridge for the proportionate arms of the 
bridge. 

A sliding contact key moves over the slide 
wire and determines the length of the arms. 
Some forms of bridges have a double or a triple 
slide wire. (See Bridge, Electric, Slide-Eormof.) 

Wire, Span The wire employed in 

systems of electric railways for holding the 
trolley wire in place. 

The span-wire is used when the poles are 
erected on both sides of the street or road-bed, 
and the trolley wire, suitably insulated from the 
span wire, is suspended therefrom. 

Wire, Suspending-, of Aerial Cable 

The wire from which an aerial cable is strung 
or suspended. 

In case the aerial cable is unusually heavy the 
suspending wire is replaced by a wire rope. (See 
Cable, Aerial.) 

Wire, Taped —A conducting wire 

covered with an insulating material in the 
shape of tape. 

A wire covered with an insulating material and 
subsequently taped is shown in Fig. 569. 



Fig. 56Q. 

Wire, Tinned 

with a coating of tin prior to its being insu- 
lated. 



Taped Wire. 

— Copper wire covered 



The coating of tin is for the purpose of insur- 
ing greater ease in soldering. It is also useful 
in case vulcanized rubber is used for the insulator, 
to prevent the sulphur from attacking the copper. 

Wire, To To fix or place the con- 
ductors or mains for any electric circuit. 

Wire, Train A line of wire em- 
ployed in a block system for railroads, con- 
nected with the general dispatcher's office, 
and used for sending train orders only. (See 
Railroads, Block System for.) 

Wire, Trolley The wire over which 

the trolley passes in a system of electric rail- 
ways, and from which the current is taken to 
drive the motors on the cars. 

A bare conductor or wire, supported over- 
head on suitable hangers and provided for 
transmitting current by the trolley to the 
motor connected with the car on the passage 
of the trolley wheel over its surface. (See 
Wheel, Trolley.) 

Trolley wires, being necessarily bare, are 
carefully insulated at their points of attachment 
to all supports. 

Wire, Trolley, Continuous A trol- 
ley wire or conductor employed in overhead 
dependent systems of electric railways. (See 
Railroads, Electric, Dependent System of 
Motive Power for \) 

Wire, Trolley, Sectional or Divided 

— A trolley wire or conductor for systems of 
electric railroads in which the wire is divided 
into a number of separate sections that are 
suitably connected with the generating dyna- 
mo by means of feeder wires. (See Rail- 
roads, Electric, DependeJit System of Motive 
Power for.) 

Wire, Trunk A main line or wire, 

extending between two distant stations, such 
as between two large cities, and provided 
solely for communication between them, not 
being tapped at intermediate points. 

Wire, Twin A conductor, consist- 
ing of two separately insulated wires, bound 
together by an additional insulating covering. 

Wire, Water-Proof A wire pro- 
tected from the weather by a coating of any 
waterproof material. 



Wir.] 



558 



[Wiiv 



Wire, Wrapped Wire that is insu- 
lated by placing strands of some insulating 
material, like cotton, parallel to its length, 
and then wrapping a number of strands 
around the wire. 

The wrapped wire is afterwards either coated 
with paraffine or other insulator, or is used with- 
out such coating. 

Wires, Bus A term sometimes used 

for omnibus bars or wires. 

The wires which receive the full current 
generated by the electric source, and carry 
it to the feeders. 

The bus-wires collect the current from all the 
sources, hence the name. 

Wires, Breaking-- Weight of The 

weight required to be hung at the end of a 
wire in order to break it. 

Ordinary copper wire will break at about 17 
tons to the square inch of area of cross- section. 
Common wrought iron breaks at 25 tons to the 
square inch. These figures are to be regarded as 
approximate only, since almost inappreciable 
differences in the physical condition of metals, as 
well as slight variations in their chemical com- 
position, often produce marked differences in 
their breaking weights. 

Wires, Cross (See Cross, Electric?) 

Wires, Crossing" — A device employed 

in telegraphic circuits whereby a faulty con- 
ductor is cut out of the circuit of a telegraph 
line by crossing over to a neighboring, less 
used, line. 

To cut out a faulty section of wire in any cir- 
cuit, such as C D, in the circuit ABCDE, Fig. 
570, a cross-connection is made to a line X Y, 
running near it, and which may be temporarily 
thrown out of use. By this means the interrup- 
tion of an important circuit may be repaired. 
A B C „ D E 



nr 



X I m Y 

Fig. 570. Crossing Wires. 

Wires, Dead Disused and aban- 
doned electric wires. 

The term dead is often applied to a wire 
through which no current is passing. The term, 
however, is more properly applied to a wire 
formerly employed, but subsequently abandoned. 



Dead wires in the neighborhood of active wire? 
are a constant menace to life and property, and 
should invariably be carefully removed. 

It is often a matter of considerable importance 
to be able to determine whether or not a current 
is passing through a wire. When the wire is not 
enclosed in a moulding, or fastened against a 
wall, this can readily be ascertained by bringing 
a small compass needle near the wire, when it 
will tend to set itself across the wire. 

The term dead wire, as will be seen, is used in 
two distinct senses. 



Wires, Leading-In 



■The wires or 



conductors which lead the current through 
(into and out of) an electric lamp. 

The term leading -in wires is generally applied 
to incandescent electric lamps, Geissler or 
Crookes tubes, and to various other apparatus. 

Wires, Leading-Up Wires em- 
ployed for raising an aerial cable to the cable 
hangers. 

Wires, Omnibus A term sometimes 

used for bus wires. (See Wires, Bus.) 

Wires or Conductors, Continuous 

Wires or conductors free from joints. 

Wires or conductors without soldered or 
twisted joints or without any joints whatso- 
ever. 

Wires, the entire lengths of which have 
been taken from the hitherto uncut coil of 
wire from the draw plate. 

Strictly speaking, any metallic circuit consists 
of a continuous wire, whether in one piece or in 
several sections or pieces. The preferable term 
would appear to be un jointed wires or conductors. 

Wires, Phantom -A term applied 

to the additional circuits or wires obtained in 
any single wire or conductor by the use of 
some multiplex telegraphic system. (See 
Telegraphy, Multiplex. Telegraphy, Syn- 
chronous-Multiplex, Delanys System?) 

Wires, Pilot In a system of incan- 
descent lighting, where a comparatively low 
potential is employed on the mains, thin wires 
leading directly from the generating station 
to different parts of the mains, in order to 
determine the differences of potential at such 
points. 



Wir. 



559 



[Wor. 



Pilot wires indicate on a voltmeter the differ- 
ence of potential at the various points. The pilot 
wires extend to the various seats of supply, and 
so give instant warning of any change in the 
value of the potential. 

Wires, Pressure In a system of 

incandescent electric lighting, wires or con- 
ductors, series-connected with the junction 
boxes, and employed in connection with suit- 
able voltmeters, to indicate the pressure at 
the junction boxes. 

The pressure wires are sometimes called the 
pilot wires. 

Wires, Tap The wires or conduc- 
tors used to carry the current from the feed- 
ers or mains at the pole to a near point on 
the trolley wire. 

Wiring 1 . — Collectively the wires or con- 
ducting circuits used in any system of electric 
distribution. 

Wiring".— Placing or establishing the wires 
or conductors for any electric circuit. 

Wiring-, Case Placing or establish- 
ing electric conductors or wires that are held 
in place on the walls or ceiling of a room, by 
means of continuous cleats. 

Wiring*, Cleat Placing or estab- 
lishing electric conductors or wires that are 
held in place on the walls or ceiling of a 
room by means of suitably shaped insulating 
cleats. 

— The conductors 



Wiring', Inside — 

that, in a system of incandescent electric 
lighting, lead to the interior of the house or 
area to be lighted. 

Wiring*, Moulding- — Electric con- 
ductors or wires that are held in place on the 
walls or ceiling of a room by means of suit- 
ably shaped mouldings. 

Work. — The product of the force by the 
distance through which the force acts. 

A force whose intensity is equal to one pound 
acting through the distance of one foot, does an 
amount of work equal to one foot-pound. 

Work is to be distinguished from the more gen- 
eral term energy. 



Work, Electric The joule. (See 

Joule?) 

The product of the volts by the coulombs. 
i joule = 10,000,000 ergs, or .73732 foot-pounds. 
" =1 volt-coulomb. 
" =1 watt for 1 second. 

Work, Electric, Unit of The volt- 
coulomb or joule. (SeeVoll-Coulomd. Joule?) 

Work, Unit of The erg. 

The amount of work done when a force of 
one dyne acts through the distance of one 
centimetre. (See Erg) 

Raising one gramme against gravity, through 
the distance of one centimetre, requires an 
amount of work equal to 980 ergs. 

Work, Units of Various units em- 
ployed for the measurement of work. 

The following table of Units of Work is taken 
from Hering's work on Dynamo-Electric Ma- 
chines : 

Work. 

1 erg = 1 dyne-centimetre. 

1 " = .0000001 joule. 

1 gramme-centimetre . . =981.00 ergs. 

I " . . = .00001 kilogr. -metre. 

I foot-grain = 1937 5 ergs. 

I 10,000,000 

•737324 

pound, 

kilogram 

.0013592 

horse- power for 

one second. 



joule, or I volt-cou- ") 
lomb, or I watt 
during every second 
or I volt-ampere 
during every] 
second J 

volt ampere during 
every second 



ergs, 
fo ot 
101937 
metre, 
metric 



foot-pound 



I 

.0013406 horse-power 

for one second. 

= .0009551 pound- 
Fall., heat unit. 

= .0005306 pound- 
Centig. , heat unit. 

= .OC02407 kilogr.- 
Centig., heat unit. 

== .0002778 watt-hour. 

= 13562600 ergs. 

= 1.35626 joules. 

=== . 13825 kilogr. metre. 

=' .0018434 metric 
horse-power for 
e second. 

= .00181818 horse- 
power for one 
second. 



WorJ oGu [Wor. 

i foot-pound = .0012953 pound- 1 horse-po'wer-hour = 2564.8 pound-Fah., 

Fah., heat unit . heat units. 

" = .0007196 pound- " = 1424.9 pound- 

Centig., heat unit. Centig., heat units. 

" =.0003264 kilogr.- " =646.31 kilogr.- 

Centig., heat unit. Centig., heat units. 

= .0003767 watt-hour. " = 745.941 watt-hours. 

I kilogram-metre = 98100000 ergs. " ....=1.01385 metric horse- 

" ■ = 9.81000 joules. power-hour. 

" = 7-233 H foot-pounds. Heat. 

= ' OI 333 metric horse- f gram . Centig = #OOI ki l gram-Centi- 

power for one grade 

second - 1 pound-Fahr = 1047.03 joules. 

= - OI 3i5i h^se power tt = m foot . pounds . 

for one second. (( = iq6 ^ kilogram . 

= .009369 pound-Fah., metres. 

heat unit << = .55556 pound-Centi- 

=.005205 pound- grade< 

Centig., heat unit. 4< =.25200 kilogram- 

=.002361 kilogr.- Centigrade 

Centig., heat unit. lt = 29o84 watt . hour . 

= .002725 watt-hour. « =.0003953 metric 

I watt-hour , = 3600 joules. horse -power-hour. 

= 2654.4 foot-pounds. (i =.0003899 horse- 

•• =366.97 kilogram, power hour. 

metres * 1 pound-Centig = 1884.66 joules. 

=3-4383 pound-Fah., it = 1389.6 foot-pounds. 

heat units. ti _ ^ ll6 k ii og ram- 

= 1.9102 pound- metres 

Centig., heat units. ti = 1.8000 pound- 

=.8664 kilogr.- Fahrenheit. 

Centig., beat units. tl = .4536 kilogram-Centi- 

=.0013592 metric grade> 

horse power-hour. f( = ^^ watt .hours. 

=.0013406 horse- M =.0007115 metric 

power-hour. horse -power-hour. 

1 metric h.-p.-hour . . . . = 2648700 joules. <4 _ tOO07OI 8 horse- 

. . . . = 1952940 foot-pounds. power-hour. 

. . . . = 270000 kilogram- f kllogram . Centig _ 4I54 . 95 jou les. 

metres - " = 3063.5 foot-pounds. 

....=2529.7 pound-Fah., ti ..=423.54 kilogram- 
heat units. t o J-r b 
, metres. 

" =1405.4 pound- 

V, J J. 7 , T , -. ' =3.9683 pound- 

Centig., heat units. ° Z, , ° ... 

. ., ~ . Fahrenheit. 

" ....= 637.5 kilogr. -Centig., ,- j r- *• 

heat units. " = 2 - 2 °46 pound-Centi- 

" =735.75 watt-hours. grade. 

. . . . = .98634 horse-power- " = I - I 542 watt hours. 

hour. " = .001569 metric horse- 

1 horse-power-hour = 2685400 joules. power-hour. 

11 = 1980000 foot- " =1.0015472 horse- 
pounds, power-hour. 
" ....=273740 kilogram- 
metres. Working, Direct The transmis- 



Won] 



561 



[Yok, 



sion of signals over a telegraph line with- 
out the use of relays or repeaters. 

"Working, Multiple, of a Dynamo-Elec- 
tric Machine A term sometimes used 

for the parallel working of dynamo-electric 
machines. (See Working, Parallel, of Dy- 
namo-Electric Machines.) 

Working:, Parallel, of Dynamo-Electric 

Machines The operation of working 

several dynamo-electric machines as a single 
source, by connecting them with one another 
in parallel or multiple arc. 

The effect of parallel working is to reduce the 
internal resistance of the dynamo. 

If a current be required in a circuit at an electro- 
motive force equal only to that of a single machine, 
and the requirements of the circuit are equal to 
the output of more than a single dynamo, a num- 
ber of dynamos must then be coupled in mul- 
tiple. 



Working. Reverse-Current 



A 



term sometimes used in telegraphy for a 
method of working by means of a double 
current in place of a single current. 

The double- current system of working was de- 
vised by Varley to permit Morse characters to be 
sent rapidly through underground conductors. 
In order to avoid the retardation due to induction, 
the current was reversed between each signal. 
This reversion in the conductor hastened the dis- 
charge of the conductor. 



Working-, Series, of Dynamo-Electric 

Machines Such a coupling of several 

dynamo-electric machines as will deliver the 
current supplied by them in series. 

As in all series connections of sources, there re- 
sults an electromotive force equal to the sum of 
the electromotive forces of the different dynamos. 

— A central core of 



Worming', Cable — 

hemp or jute around which are wrapped the 
several separate conductors of a cable con- 
taining more than a single separate conduc- 
tor. 

Wood's Button Repeater. — (See Repeat- 
ers, Telegraphic^) 

Wrapped Wire. — (See Wire, Wrapped.) 

Writing-. Electrolytic Imprinting 

written characters on cloths, or other textile 
fabrics, by the electrolytic decomposition of a 
dyeing substance with which they are im- 
pregnated. 

The cloths, etc., to be written on, are impreg- 
nated with an aniline salt, and placed on an insu- 
lated metallic plate next to the salt, which is con- 
i.ected to one pole of an electric source. The 
other pule is connected to a carbon electrode, 
which is used as the writing stylus or pencil. By 
suitably connecting the terminals the writing is 
obtained in color on a white ground, or m white 
on a colored ground. (See Dyeing, Electric.) 

Writing; Telegraphy. — (See Telegraphy, 
Writing A 



Y-Shaped Sparks. — (See Spark, 
Y-Shaped.) 
Yale-Loek-S witch Burglar Alarm. — See 

Alarm, Yale-Lock-Switch Burglar.) 

Yoke. Multiple-Brush — A term 

sometimes applied to multiple brush rocker 
of a dynamo or motor. (See Rocker, Mul- 
tiple-Pa ir Brush . ) 

Yoke, Multiple-Pair Brush A 

device for holding a number of pairs of 
brushes of a dynamo-electric machine in such 



a manner that they can be readily moved or 
rotated on the commutator cylinder. 

The brushes are placed side by side on the com- 
mutator cylinder. In such cases the several pairs 
of brushes are so arranged that they can be 
thrown off or out of contact with the commutator 
cylinderwhile cleaning the cylinder, without stop- 
ping the machine. 



Yoke, Single-Brush 



— A term some- 
times used for single-brush rocker. (See 
Rocker, Single-Brush.) 



Yok.] 



562 



[Zon. 



Yoke, Single-Pair 



-A single-brush 



rocker. (See Rocker, Single-Brush) 

Yoke, Single-Pair Brush A device 

for holding a single pair of collecting brushes 
of a dynamo-electric machine in such a way 



that they can be readily moved or rotated on 
the commutator cylinder. 

Yoked-Horseshoe Electro-Magnet. — (See 
Magnet, Electro, Yoked-Horseshoe.) 



Z.— A symbol sometimes used in electro- 
therapeutics for contraction. 

The use of Z, is for the purpose of avoiding 
the letter C, which has already been used for cur- 
rent or ampere in Ohm's law. Increasing 
strengths of contraction are represented by Z', 
Z", Z'". 

Z. — A symbol for electro-chemical equiva- 
lent. 

Zero, False — A zero taken midway 

between any two equal and opposite deflec- 
tions of a measuring instrument. 

Zero, Inferred A zero deduced or 

inferred from the deflection produced by a 
charge that is to be measured by comparison 
with the value of the deflection by means of 
a known charge in an electrical measuring 
instrument. 

An inferred zero is usually completely off the 
scale, hence its name. It does not actually exist. 

Zero Methods.— (See Method, Null or 
Zero?) 

Zero Potential. — (See Potential, Zero.) 

Zero, Shifting A zero that changes 

or shifts in position ; a polar zero in a measur- 
ing instrument. 

Zigzag Electro-Magnet. — (See Magnet, 
Electro, Zigzag) 

Zigzag Electromotive Force.— (See 
Force, Electro?notive, Zigzag.) 

Zigzag Lightning. — (See Lightning, Zig- 
zag.) 

Zinc, Amalgamation of The cov- 
ering or amalgamation of zinc with a layer 
of mercury. 

To amalgamate a plate of zinc, its surface is 
first thoroughly cleaned by immersing the plate in 
dilute sulphuric acid of about I part of acid to 



10 or 12 parts of water. A few drops of 
mercury are then rubbed over its surface, thus 
coating it with a bright metallic film of zinc 
amalgam. Care must be taken not to use too 
much mercury, since the zinc plate would thus be 
rendered brittle. 

Zinc-Carbon Yoltaic Cell.— (See Cell, 
Voltaic, Zinc-Carbon.) 

Zinc-Copper Yoltaic Cell.— (See Cell, 
Voltaic, Zinc-Copper^ 

Zinc, Crow-Foot — A crow-foot- 
shaped zinc used in the gravity voltaic cell. 
(See Cell, Voltaic, Gravity) 

The term "crow-foot " refers to the shape of 
the claws. It is hardly a happy term. 

Zinc-Lead Yoltaic Cell.— (See Cell, Vol- 
taic, Zi7ic-Lead) 

Zinc Sender. — (See Sender, Zinc.) 

Zincode of Yoltaic Cell. — A term for- 
merly employed to indicate the zinc terminal 
or electrode of a voltaic cell. 

The negative electrode or kathode are prefer- 
able terms. 

Zone, Anelectrotonic — A name 

sometimes given to the polar zone. (See 
Zone, Polar.) 

Zone, Kathelectrotonic A name 

sometimes given to the peripolar zone. (See 
Zone, Peripolar.) 

Zone, Peripolar A term proposed 

by De Watteville for the zone or region sur- 
rounding the polar zone on the body of 
a patient undergoing electro-therapeutic 
treatment. 

Zone, Polar A term proposed by 

De Watteville for the zone or region surround- 
ing the therapeutic electrode applied to the 
human body for electric treatment. 



THE FIRST SYSTEMATIC TREATISE ON THE ELECTRIC RAILWAY. 



THE ELECTRIC RAILWAY 

IN THEORY MND PRACTICE, 
By O. T, CROSBY AND DR. LOUIS BELL. 



Covering the Genera/ Principles of Design, Construction and Operation. 




OCTAVO, 400 PAGES AND i 79 ILLUS- 
TRATIONS, PRICE, $2.50 



TABLE OK CONTENTS: 



Chapter I. General Electrical Theory. II. Prime 
Movers. III. Motors and Car Equipment IV. The 
Line. V. Track, Car Houses, Snow Machines. VI. 
The Station. VII. The Efficiency of Electric Traction. 
VIII. Storage Battery 
Traction. IX. Mis- 
cellaneous Methods of 
Electric Traction. X. 
High Speed • Service. 
XL Commercial Con- 
siderations. XII. His- 
torical Notes. 



O. T. CROSBY. 



APPENDICES 




DR. LOUIS BELL. 



Appendix A. Electric Railway vs. Telephone Decisions. 
13. Instructions to Linemen. C. Engineer's Log Book. 
D. Classification of Expenditures of Electric Street Rail- 
ways. E. Concerning Lightning Protection, by Prof. 
Elihu Thomson. 

In this important new book just issued will be found 
a full discussion of the principles, apparatus and methods 
of construction employed in electric railroading. As will 
be seen from the table of contents, it treats all departments 
of the subject as comprehensively as is practicable in a volume of reasonable size. The illus- 
trations have been prepared especially for it, and many of them are entirely new. 

To Electric Railway Managers, Superintendents, Electricians and Operators, this volume 
is invaluable, while no one interested in the modern applications of electricity will want to be 
without it. The necessity for such a book has been keenly felt, 

Copies of The Electric Railway in Theory and Practice, or of any other Electrical 
work published, will be mailed to any address, Postage Prepaid, on receipt of price. Address 

THE W. J.JOHNSTON COMPANY, Ltd. 

TIJVIES BUIbDIN©, NEW YORK. 



FIRST AMERICAN BOOK ON ELECTRIC MOTORS, 

THE ELECTRIC MOTOR 

HND ITS HPPLICHTI0NS. 

By T. C. Martin and Jos. Wetzler. 

With an Appendix on the Development of the Electric Motor since 1888. 

By Dr. Louis Bell. 

This is the first American Book on Electric Motors, and the only one in any language dealing exclu- 
sively and iully with the modern Electric Motor in all its various practical applications. 



CONTBNTS 



Chapter 



i. Elementary Considerations 1 

ii. Early Motors and Experiments 

in Europe 8 

iii. Early Motors and Experiments 

in America 13 

iv. The Electrical Transmission of 

Power 29 

v. The Modern Electric Railway 

and Tramway in Europe 48 

vi. The Modern Electric Railway 

and Street Car Line in America 61 
The use of Storage Batteries 

with Electric Motors for 

Street Rvs 99 

The Industrial Application of 

Electric Motors in Europe 114 



vii 



125 



PAGE. 

Chapter ix. The Industrial Application of 

Electric Motors in America. . . 
" x. Electric Motors in Marine and 

Aerial Navigation 137 

Telpherage 143 

Latest American Motors and 

Motor Systems 152 

Latest American Motors and 

Motor Systems Con 196 

Latest European Motors and 

Motor Systems 246 

Alternating Current Motors — 255 

Thermo-Magnetic Motors 272 

The Development of the Electric 

Motor since 1888 27? 



XI. 

fxii. 



" XV. 

" xvi. 
Appendix. 



15 Pages. 353 Illustrations. Price, $3.00. 



The W. J. JOHNSTON CO., Lil. 167-176 Times Building, New York. 

THE LEADING AMERICAN BOOK ON DYNAMOS. 



Principles of Dynamo-Electric Machines, 

And Practical Directions for Designing and Constructing Dynamos. 

With an Appendix containing several articles on allied subjects and a table 

of equivalents of units of measurement. 

By Cael Hering. 



CONTENTS. 

Chapter I., Review of Electrical Units and Fundamental Laws; Chapter II., Fundamental Principles of 
Dynamos and Motors ; Chapter III., Magnetism and Electromagnetic Induction; Chapter IV., Generation of 
Electromotive Force in Dynamos; Chapter V, Armatures; Chapter VI., Calculation of Armatures; Chapter 
VII., Field Magnet Frames; Chapter VIII., Field Masrnet Coils; Chapter IX., Regulation of Machines; Chap- 
ter X., Examining Machines; Appendix I , Practical Deductions from the Franklin Institute Tests of 
Dynamos; Appendix II., The So-called " Dead Wire' 1 on Gramme Armatures; Appendix III., Explorations 
of Magnetic Fields surrounding Dynamos; Appendix IV., Systemsof Cylinder- Armature Windings; Appendix 
IV., Systems of Cylinder-Armature Windings"; Appendix V., Equivalents of Units of Measurements (Table). 

American electricians have long felt the need of a work of this natnre, written in plain and simple lan- 
guage by a man thoroughly familiar with all types of generating apparatus. The book is copiously illus- 
trated, printed on an extra good quality of paper, and substantially bound. 

Cloth, 279 Pages. 59 Illustrations. Price, $2.50 

Copies of the above, or of any other electrical book or books published, will be promptly mailed to any 
address in the world, postage prepaid, on receipt of price. Address : 

The W. J. JOHNSTON CO., Li, Times Building, New York. 



Complete Kules for the Safe Installation of Electrical Plants. 



ELECTRIC 



L 




niiir 





FOR THE USE OF 



ENGINEERS AND ARCHITECTS 



By E. A. MERRILL. 

The author has drawn up a set of specifications covering the various classes of lighting 
installations, which may serve as forms for any special type or character of plant, and which 
are at the same time full enough to cover the ordinary installation of electrical apparatus and 
electric light wiring. The book will prove especially useful to architects and engineers who 
desire a full knowledge of the necessary requirements of the various classes of electrical in- 
stallations in order to meet the demands of the insurance inspectors and the conditions of 
safety. 

THE LATEST RULES ARE GITEN OF THE 

(1) National Electric Ligiit Association. 

(2) National Board of Fire Underwriters. 

(3) New England Insurance Exchange. 

OTHER CONTENTS: 

Specifications for the Installation of Electric Lighting Plants. — General 
Specifications. — Installation of Dynamos and Switchboards. — Alternate 
Current Converter System, Constant Potential. — General Specifications 
for Alternate or Direct Current Dynamos for Parallel System of Distribu- 
tion. — Arc Dynamos. — Fixtures, etc. — Interior Wiring. — Two-Wire, Direct 
or Alternating Current System. — Three- Wire System. — Three- Wire System 
Adapted to Two-Wire System. — Arc System. — Conduit System, Two- 
Wire. — Interior Wiring for Central Station Plants. — Pole Lines. — Low 
Potential, Direct Current, Two or Three-Wire. — Alternating System.— 
Street Lighting Circuits. — Specifications for Steam Plant. 



Bound in Clotti. 



Price 



INCLUDING 
POSTAGE, 



$1.50. 



Copies of MERRILL'S ELECTRIC LIGHTING SPECIFICATIONS, or of any other 
Electrical book or books published, will be mailed to any address in the world, postage pre- 
paid, on receipt of the price. Address: 

The W. J. JOHNSTON COMPANY, Ld., Times Build'g, NEW YORK. 



RECORD OF AN ACTIVE FIELD OF DEVELOPMENT. 



RECENT PROGRESS 

IN 

ELECTRIC RAILWAYS 

By Carl Hering. 




Compiled and Condensed from Current Electrical Literature, 

About 400 pages and 120 Illustrations. Cloth, Price $1.00. 

The volume of electrical literature has now assumed such propor 
tions that it is impossible to keep abreast of it, much less to make such 
records or abstracts as would be of use for future reference. To 
meet the demand of those interested in the progress of Electric Rail- 
ways, and who have felt the want of a general index to recently pub- 
lished matter on this subject, this compilation has been prepared. The 
book contains a classified summary of the recent literature on this active 
and promising branch of electrical progress and descriptions of new 
apparatus and devices of interest to the technical reader. 



CO NTK NTOS. 

Chapter I. Historical. Chapter II. Development and 
Statistics* Chapter III. Construction and Operation. 
Chapter IV. Cost of Construction and Operation. 
Chapter V. Overhead Wire Surface Roads. Chapter 

VI. Conduit and Surface Conductor Roads. Chapter 

VII. Storage Rattery Roads. Chapter VIII. Under- 
ground Tunnel Roads. Chapter IX. High Speed In- 
terurban Railroads. Chapter X. Miscellaneous Systems. 
Chapter XI. Generators) motors and Trucks. Chap- 
ter XII. Accessories. 



CARL HERING. 



TESLA'S LONDON LECTURE. 



EXPERIMENTS WITH ALTERNATE CURRENTS 

Of High Potential and High Frequency. 

By Nikola Tesla. 



156 Pages, with Portrait and 35 Illustrations. Cloth, $1.00. 

This book gives in full Mr. Tesla's important lecture before the 
London Institution of Electrical Engineers, which embodies the 
results of years of patient study and investigation on Mr. Tesla's part 
of the phenomena of Alternating Currents op Enormously High 
Frequency and Electromotive Force. 

Every Electrician, Electrical Engineer or Student of 
Electrical Phenomena who makes any pretensions to 
thorough acquaintance with recent progress in this 
important field of research which Mr. Tesla has so 
ably developed must read and reread this lecture. 

The book is well illustrated with 35 cuts of Mr. Tesla's experimental 
apparatus, and contains in addition a biographical sketch, accompanied 
by a full-page portrait, which forms a fitting frontispiece to a lecture 
which created such widespread interest. 

Copies of the above or of any other Electrical Books published, 
will be promptly mailed to any address on receipt of price. Address 




NIKOLA TESLA. 



The W. J. JOHNSTON CO., Limited. Times Building, New York. 



A BOOR FOR EVERY DEALER AND EVERY BUYER. 



JOHEIsrSTODST'S 

Electrical^Street Railway 

DIRECTORY. 



Published Annually. -:- Price, in Cloth, (! n S^T^Vo°m J ) $5.00. 



THIS BOOK CONTAINS: 

A LIST OF CENTRAL ELECTRIC LIGHT AND POWER STATIONS, 

with the Number of Lights in Use, Electric Power Supplied, Capital Paid in. Name of System, Name 
of Managing Official, Superintendent, Purchasing Agent, Electrician, and other particulars. 

A LIST OF ISOLATED ELECTRIC LIGHT PLANTS, 

with Name of Electrician, Purchasing Agent, Engineer, System and Size of Plant, and other particulars. 

A LIST OF STREET RAILWAY COMPANIES, 

with Length of Road, Number of Cars, Car Miles Run, Capital Paid in, Managing Official, Superinten- 
dent, Purchasing Agent, System— Electric, Horse or Cable— and other particulars. 

A LIST OF EVERY MANUFACTURER AND SUPPLY DEALER 

connected with the Electrical or Street Railway Industry. 



A special effort is made to have this Directory the most complete, the 
most reliable and the most valuable of any work of the kind issued. Its 
pages are full of interest not only to every dealer in Electrical and Street 
Railway Apparatus, Machinery and Supplies, and every manufacturer 
who wishes to reach those engaged in this large, important and growing 
industry, but to the purchasers of Electrical Apparatus and Supplies and 
to all in any way interested in the progress and development of either the 
Electrical or the Street Railway business. 

Copies of Johnston's Electrical and Street Railway Directory, or 

of any other Electrical or Street Railway books, will be mailed to any 
address in the world, postage prepaid, on receipt of the price. Address : 

THE W. J. JOHNSTON COMPANY, Ltd., 
167-176 Times Building, NEW YORK. 



AUTHORIZED AMERICAN EDITION, 



By Prof. Silvanus P. Thompson, D.SC, B.A., M.I.E.E. 

A full theoretical and practical account of the properties and peculiarities of electromagnets: together with- 
complete instructions for designing magnets to serve any specific purpose. Published with the 
express consent and careful revision of the author. 

Clotli, 280 Pages. 75 Illustrations. Price $1.00. 

GONTeNTS. 

Lecture I. — Introductory ; Historical Sketch ; Generalities Concern- 
ing Electromagnets ; Typical Forms ; Polarity; Uses in General ; The 
properties of Iron ; Methods of Measuring Permeability; Traction Meth- 
ods; Curves of Magnetisation and Permeability; The Law of the Elec- 
tromagnet; Hysteresis; Fallacies and Facts about Electromagnets. 

Lecture IL— General Principles of Design and Construction; Prin- 
ciple of tne Magnetic Circuit. 

Lecture III.— Special Designs; Winding of the Copper; Windings 
for Constant Pressure and for Constant Current; Miscellaneous Rules 
about Winding; Specifications for Electromagnets; Amateur Rules 
about Resistance of Electromagnet and Battery; Forms of Electromag- 
nets; Effect of Size of Coils; Effect of Position of Coils; Effect of Shape 
of Section; Effect of Distance between Poles: Researches of Prof. 
Hughes ; Position and Form of Armature : Pole-Pieces on Horseshoe 
Magnets ; Contrast between Electromagnets and Permanent Magnets; 
Electromagnets for Maximum Traction; Electromagnets for Maxi- 
mum Range of Attraction ; Electromagnets of Minimum Weight ; A 
useful Guiding Principle ; Electromagnets for Use with Alternating 
Currents; Electromagnets for Quickest Action; Connecting Coils for 
Quickest Action; Battery Grouping for Quickest Action; Snort Cores 
vs. Long Cores. 
prop, silvanus p. Thompson. Lecture IV.— Electromagnetism and Electromagnetic Mechanism. 




THE ONLY BOOK TREATING OF THIS SUBJECT EXCLUSIVELY. 



THE! C^TT^DD 



XT 



By Wm, Maver, Jr., and Minor M. Davis. 

With Chapters on The Dynamo-Electric Machine in Relation to the Quadruplex. 

The Practical Working of the Quadruplex. Telegraph Repeaters and 

the Wheatstone Automatic Telegraph. Ry WM. MAYER, Jr. 



O O N T 

Development of the Quadruplex. 

Introduction and Explanatory. 

The Transmitter, Rheostat and the Condenser, 

Stearns Duplex 

Instruments of the Polar Duplex. 

Tiie Polar Duplex. 



r M T S. 
The Quadruplex. 
The Dynamo-Electric Machine in relation to the 

Quadruplex. 
The Practical Working of the Quadruplex. 
Telegraph Repeaters. 
The Wheatstone Automatic Telegraph. 



This book is written in plain, simple and explicit language, and is within the ready comprehension of all. 
The illustrations are numerous, and with their aid the readers can at once grasp, mentally, the operation of 
the Quadruplex. The book is handsomely printed on fine paper and substantially bound. Every Telegrapher 
and every Electrician should have a copy. 

Cloth, 126 Pages. 63 Illustrations. Price, $1.50. 

THE TELEPHONE MAN'S TEXT BOOK. 

PRACTICAL INFORMATION FOR TELEPHONISTS. 

By T. D. Lockwood, Electrician, American Bell Telephone Company. 
CONTENTS. 
Historical Sketch of Electricity from 600 B. C. to 18S2 A. D. 
Facts and Figures about the Speaking Telephone. 
How to Build a Short Telegraph or Telephone Line. 
The Earth and Its Relation to Telephonic Systems of Communication. 
The Magneto-Telephone— What it is, How it is Made, and How it Should 

be Handled. L 

The Blake Transmitter. ^ 

Disturbances Experienced on Telephone Lines. 
The Telephone Switch-Board. 
A Chronological Sketch of the Magneto-Bell, and How to Become 

Acquainted with it. 
Telephone Transmitter Batteries. 
Lightning— Its Action upon Telephone Apparatus— How to Prevent 

or Reduce Troubles Arising Therefrom. 
The Telephone Inspector. 
The Telephone Inspector— His Daily Work. 
The Inspector on Detective Duty. 
The Daily Routine of the Telephone Inspector 
Individual Calls for Telephone Lines. 
Telephone Wires versus Electric Light Wires. 
Electric Bell Construction, Part I. 
Electric Bell Construction, Part II. 
Housetop Lines, Pole Lines and Aerial Cables. 
Anticipations of Great Discoveries and Inventions. 

12mo. 192 Pages ; Cloth. Price, $1.00. 
Copies of the above books, or of any other electrical book or books published, will be promptly mailed 
to any address in the world, postage prepaid, on receipt of price. Address :— 

THE W. J. JOHNSTON CO., Lim., TIMES BUILDING, N. Y. 




T. D. LOCKWOOD. 



RECOMMENDED BY 

THE ELECTRICAL WORLD FOR SPECIAL READING. 



TTe are often asked by those who desire to inform themselves in regard to electrical 
matters to recommend to them a course of reading or book on particular subjects or in relation 
to certain special departments of electrical application. The following list will, we trust, 
meet the requirements of most of those who desire such information. "With scarcely an 
exception, the books mentioned are substantially bound in cloth and copiously illustrated. 



(A.) PRINCIPLES AND THEORY OF ELECTRICITY AND MAGNETISM. 
(1.) An Elementary Course. 

PRICE. 

Atkinson's Elements of Static Electricity, with a full description of the Holtz and Topler 

Machines Si. 50 

Atkinson's Elements of Dynamic Electricity and Magnetism 2. 00 

Ayrton's Practical Electricity for First Year Students 2.50 

Electrician Primers, vol. I, Theory. $1.00: vol. n, Practice 1.00 

Fleming's Short Lectures to Electrical Artisans 1.50 

Houston's Dictionary of Electrical Words, Terms and Phrases. Second edition, entirely re- 
written, containing about 5,000 distinct titles. 570 illustrations and 562 double column pages. Svo. 5.00 

Jenkin's Electricity and Magnetism, with an Appendix on the Telephone and Microphone 1.50 

Kennelly 6c Wilkinson's Practical Notes for Electrical Students 2.50 

JIaycock's First Book of Electricity and 3Ia2metism 0.60 

Thompson's Elementary Lessons in Electricity and Magnetism 1.25 

Thompson's Lectures on the Electromagnet ... 1.00 

(2.) An Advanced Course. 

Cumming's Introduction to the Theory of Electricity $2 .25 

Emtage's Introduction to the Mathematical Theory of Electricity and Magnetism 1 .90 

E wing's Magnetism of Iron and other Metals (new) 4 00 

Pleming's Alternate Current Transformer in Theory and Practice. S vols., second vol. in press. 3.00 

Faraday' s Experimental Researches in Electricity. 3 vols 90 . 00 

Houston's Dictionary of Electrical "Words, Terms and Phrases, second edition, entirely re- 
written, containing about 5.000 distinct titles, 570 illustrations and 562 double column pages Svo. 5.00 

Lodge's Modern Views of Electricity 2.00 

IWascart 6c Jonbert's Treatise on Electricity and Magnetism. 2 vols 15 00 

Maxwell's Treatise on Electricity and Magnetism. 2 vols. New edition 8.00 

Thompson's Electromagnet and Electromagnetic Mechanisms 6 00 

"Watson 6c Burbury's Mathematical Theory of Electricity and Magnetism. 2 vols 5 .50 

(B.) PRACTICAL APPLICATIONS OF ELECTRICITY AND MAGNETISM. 

(1 ) General Treatises. 

Electricity in Daily Life 

Hospitaller's Modern Applications of Electricity 2 vols 

Houston's Dictionary of Electrical "Words, Terms and Phrases, second edition, entirely re- 
written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. 

Guillemin's Electricity and Magnetism 

Slingo 6c Brooker's Electrical Engineering for Electric Light Artisans and Students 

Trevert's Electricity and Its Recent Applications 

W oj-mell's Electricity in the Service of Man . 



S3 00 


8 00 


5 00 


8 00 


3.50 


2. 00 


6 00 



(2.) Special Treatises. 

(a.) Electric Lighting. 

PRICE. 

Alglave & Boulard's Electric Light: Its History, Production and Application 5.00 

Atkinson's Elements of Electric Lighting 1.50 

Day's Electric Light Arithmetic 0.40 

Desmond's Electricity for Engineers 2.50 

Dredge's Electric Illumination. Vol. I., $15., Vol. II „ 7.50 

Gordon's Decorative Electricity 3.75 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re-writ- 
ten, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. . . 5.00 

Latimer's Incandescent Electric Lighting , 0.50 

Merrill's Electric Lighting Specifications, for the use of Engineers and Architects 1 . 50 

Russell's Electric Light Cables 1.50 

Urquhart's Electric Light : Its Production and use . 3.00 

Urquhart's Electric Light Fitting 2.00 

(b.) The Electric Motor. 

Badt's Electric Transmission Hand-book 1 .00 

Bot tone's Electro-motors ; How Made and How Used .50 

Crosby & Bell's Electric Railway in Theory and Practice 2.5fr 

Bering's Recent Progress in Electric Railways ... 1 .00 

Houston's Dictionary of Electric Words, Terms and Phrases, second edition, entirely re-written, 

containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo . . .*. ". ... 5 00 

Kapp's Electric Transmission of Energy 3.00 

Martin & Wetzler's Electric Motor and Its Applications ; with an Appendix by Dr. Louis Bell. 3.00 

Urquhart's Electro-motors 3.00 

(c.) Telegraphy. 

Abernethy's Commercial and Railway Telegraphy 2.00 

Houston's Dictionary of Electrical Words, Termsand Phrases, second edition, entirely re-written, 

containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5.00 

Lockwood's Electricity, Magnetism, and Electric Telegraphy 2.50 

Maver & Davis' Quadruplex, with Chapters on Telegraph Repeaters and the Wheatstone 

Automatic Telegraph 1.50 

Pope's Modern Practice of the Electric Telegraph 1 .50 

Preece & Siverwright's Telegraphy 1.75 

Prescott's Electricity and the Electric Telegraph. Two vols 7.00 

Plum's Military Telegraph During Our Civil War. Two vols 5.00 

Beid's Telegraph in America 5.00 

(d.) The Telephone. 

Du Moncel's Telephone, The Microphone and the Phonograph , — 1 .25 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re-written 

containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo ... 5.00 

Lockwood's Practical Information for Telephonists 1 .00 

Poole's Practical Telephone Hand-book 1.25 

Preece & Maier's Telephone 4.00 

Prescott's Bell's Electric Speaking Telephone 6.00 

(e.) Electro-Metallurgy 

Bonney's Electro-platers' Hand-book 1.20 

Gore's Art of Electrolytic Separation of Metals, etc 3.50 

Gore's Theory and Practice of Electro-deposition 0.80 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re-written, 

containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5.00 

Urquhart's Electrotyping ' 2.00 

Wahl's Galvanoplastic Manipulation 7.50 

Watt's Electro-deposition '._. . . 1 3.50 

(f.) Batteries. 

Carhart's Primary Batteries • 1 - 50 

Gladstone & Tribe's Chemistry of Secondary Batteries of Plante and Faure 1.00 

Houston's Dictionary of Electrical Words,Terms and Phrases, second edition, entirely re- written, 

containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo 5.00 

Niaudet's Elementary Treatise oh Electric Batteries. 2.50 



PRICE. 

Niblett's Secondary Batteries , 1.5a 

Reynier's Voltaic Accumulator 3.00 

Salomons' Electric Light Installation and the Management of Accumulators 2.00 

(g.) The Dynamo, 

ISatlt's Dynamo Tenders' Hand-book $1.00 

Itottonc's Dynamo : How Made and How Used l.OO 

Croft's How to Make a Dynamo .80 

Bering's Principles of Dynamo Electric Machines 2.50 

Thompson's Dynamo Electric Machinery. New. Fourth edition. Revised. Re-written 9.00 

Walker's Practical Dynamo Building for Amateurs .80 

(h.) Alternating Currents. 

Blakesley's Papers on Alternating Currents of Electricity. Reprinting • 

Desmond's Electricity for Engineers 2.50 

Fleming's Alternate Current Transformer in Theory and Practice 3.00 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- 
written, containing about 5,000 distinct titles, 570 illustrations and 562 double-column pages. 

8vo 5.00 

(C.) ELECTRICAL TESTING AND MEASUREMENT. 

Ayrton's Practical Electricity $2.50 

Gray's Absolute Measurement in Electricity and Magnetism 1 .25 

Bering's Table of Equivalents of Units of Measurement , 0.50 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- written, 

containing about 5,000 distinct titles, 570 illustrations and 562 double-column pages. 8vo 5.00 

BLempe's Hand-book of Electrical Testing 5.00 

Lochwood's Electrical Measurement and the Galvanometer 1.50 

Swinburne's Practical Electrical Measurement 1 .75 

Webb's Testing of Insulated Wires and Cables 1 .00 

(D.) MISCELLANEOUS. 

Allsop's Practical Electric Bell Fitting $1 .25 

Atkinson's Elements of Static Electricity 1 .50 

Gray's Electrical Influence Machines ^ 1 .75 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- 
written, containing about 5,000 distinct titles, 570 illustrations and 562 double column pages. 8vo. 5.00 

Bering's Universal Wiring Computer 1 .00 

Tesla's Experiments with Alternate Currents of High Potential and High Frequency — ► 1 .00 

(E.) BOOKS FOR THE N0N-TECHN1CAL READER. 

Benjamin's Age of Electricity $2.00 

Guillemin's Electricity and Magnetism _ 8.00 

Hospitaller's Modern Applications of Electricity. Two vols 8.00 

Houston's Dictionary of Electrical Words, Terms and Phrases, second edition, entirely re- 
written, containing about 5, 000 distinct titles, 570 illustrations and 562 double column pages. 8vo. 5 . 00 

Keid's Telegraph in America 5.00 

"Wormell's Electricity in the Service of Man 6.00 

(F.) HISTORICAL WORKS. 

Alglave ik Boulard's Electric Light $5.00 

Dredge's Electric Illumination. Vol. I, $15.00, vol. II 7.50 

Fable's Histoiy of Telegraphy to 1837 3.00 

Martin & Wetzler's Electric Motor and Its Applications 3.00 

Pope's Evolution of the Electric Incandescent Lamp 1.00 

Prescott's Telephone 6.00 

Reid's Telegraph in America. 5.00 

Thompson's Dynamo Electric Machinery. New. Fourth edition. Revised. Re-written 9.00 

Thompson's Philipp Reis, Inventor of the Telephone 3.00 

Copies of any of the books mentioned above, or of any other electrical books published, 

will be mailed, postage prepaid, to any address in the world on receipt of the price. 

Addrpss * 

THE W. J. JOHNSTON COMPANY, LIMITED 
167-176 TIMES BUILDING, NEW YORK. 



THE PIONEER ELECTRICAL JOURNAL OF AMERICA, 




■'/';;'■'•" 



HANDSOMELY AND PROFUSELY ILLUSTRATED, 

IS PUBLISHED EVERY SATURDAY BY 

THE W. J. JOHNSTON COMPANY, Ltd. 

Established 1874. Incorporated 1889. 
Telephone Call: CORTLANDT 924. Cable Address: "ELECTRICAL," NEW YORK. 

Publication Offices : 167-176 TIMES BDILDING, HEW YORK. 

Kew England Office : 620 Atlantic Avenue, Boston. | Western Office: 465 "The Bookery," Chicago. 
Philadelphia Office: 927 Chestnut Street. 



THE ELECTRICAL WORLD is noted for its ability, enterprise, in- 
dependence and honesty. For thoroughness, candor and progressive spirit it 
stands in the foremost rank of special journalism. 

DURING 1893 

more money will be spent than in any previous year to enable it to keep its 
readers abreast of electrical progress and to sustain its reputation, not only 
as the pioneer electrical weekly of America, but as the leading journal of 
its class, and the periodical with the largest circulation of any electrical 
journal published. 

AS EVERY ONE ACQUAINTED WITH THE SUBJECT KNOWS, THE ELECTRICAL 

WORLD is the largest, most original and most handsomely and profusely 
illustrated of all the journals in the world devoted to Electricity. No one in 
any way interested in electrical progress and development can afford to miss read- 
ing it for a single issue. 

SUBSCRIPTIONS, including postage to any part of the United States, 
Canada or Mexico, $3.00 a year. This is a merely nominal price for such a journal. 
Addresses are changed as often as desired without extra charge. Foreign countries 
in the U. P. U., $6.00 a year. 

Ant newsdealer will supply The Electrical World regularly at 10c. a 
week. Newsdealers, Postmasters and Electrical Supply Houses receive subscrip- 
tions, or remit $3.00 for one year, direct to the Publishers, 

THE W. J. JOHNSTON COMPANY, Ltd., Times Building, New York, 

OR ANY OF THE BRANCH OFFICES AS ABOVE. 



